RIXIMKA DUMARKA: VASA RECTA JUXTAMEDULLARY NEPHRON

UTERUS

The uterus (Latin: uterus) is the female reproductive organ of humans. In this text, you will read all about the uterus and its functions. Anatomy of the Uterus The most important function of the uterus, is to accept a fertilized embryo which implants into its lining. After implantation, the embryo will develop into a fetus and it will stay inside the uterus until birth. The human uterus consists of two segments, being: The body of the uterus (Latin: corpus uteri). This is the largest part of the uterus and is also where the implantation of the embryo takes place. This part of the uterus is also connected to the fallopian tubes. The cervix (Latin: cervix uteri; often abbreviated as cervix). The cervix consists of the neck of the cervix and the ectocervix (often referred to as the ‘portio’). The ectocervix is visible and palpable inside the vagina and is therefore also the connection with the vagina. De portio (the ectocervix) is lined with squamous epithelium, the endocervical canal with mucus producing glandular epithelium. The shape of the uterus The human uterus is pear shaped. Yet the shape of the uterus varies from organism to organism. For instance, animals that generally bear more than one young have two uterine horns (cornua uteri), one left and one right. This way, each uterine horn can harbour one or more young. The size of the uterus of an adult woman is about 5 to 10 centimetres. The uterus of a woman who has never been pregnant before is about the size of a mandarin. After the first pregnancy (and birth) the uterus is slightly bigger. During pregnancy, the uterus will expand and become heavier. The uterus of a pregnant woman can reach a weight of a kilogram. This weight does not include the placenta, amniotic fluid and fetus. When the woman hits menopause, the uterus will shrink slightly. Position of the Uterus The uterus lies deep in the abdomen. To be more precise, the uterus lies within the pelvic diaphragm, directly behind the bladder and in front of the rectum. There are several ligaments that hold the uterus in place. The broad ligament (ligamentum latum) and the round ligament (ligamentum rotondum) are the most important ligaments. What does the uterine wall consist of The uterine wall consists largley of smooth muscle tissue. This layer is called the myometrium. During labour, this smooth muscle tissue will contract (contractions) in order to push the baby out of the body. Just like any organ in the human body, the uterus also needs blood. This blood is supplied by two uterine arteries. The Latin names of these arteries are aa. uteria. These arteries are situated on the left and on the right of the uterus. The endometrium The endometrium is also referred to as the uterine lining and it lines the entire uterine cavity. The endometrium reacts strongly to two female hormones, estrogen and progesterone. Under the influence of estrogen, the uterine lining becomes thicker. The hormone progesterone stimulates the production of more mucus glands. Once the progesterone levels drop (there is less progesterone to be found in the body), the mature and thick uterine lining can no longer stay intact and it must leave the body. When the uterine lining leaves the body through the vagina, we call this menstruation. What many people don't know, is that the endometrium consists of two layers, namely the: Basal layer (lamina basalis). This basal layer always remains present inside the uterus. Functional layer (lamina functionalis). This layer is shed during menstruation and will build up again from the basal layer. Abnormalities and diseases of the uterus There are several abnormalities and diseases that can occur in the uterus. The following abnormalities and diseases may occur in the uterus: Inflammation of the endometrium (endometritis). Polyps Hyperplasia Uterine Cancer Fibroids Malignant tumor Trophoblast abnormalities Cervix polyp Warts Extropion Endometriosis Cervical Cancer Examination of the uterus There are several reasons why an examination of the uterus may be necessary. For example, a woman who consults her GP due to specific symptoms, if a woman is pregnant, or if a woman needs to be examined for uterine cancer. Examination of the uterus can be done in several ways, the method used depends on the reason for the examination. The uterus can be examined in the following ways: Vaginal examination Speculum examination Ultrasound Hysteroscopy Laparoscopy The uterus and the orgasm When a woman is sexually aroused, the uterus will erect slightly. The uterus is pulled in an upward direction, making the vagina slightly longer. When a women has an orgasm, the pelvic muscles and the uterine muscle contract. There are women who barely feel the contraction of the uterine muscle, but there are also women who find that these contractions produce a very pleasant feeling. When the woman has had an orgasm, it can take up to ten minutes before the uterus has returned to its normal position. The Cervix The cervix (also referred to as the cervix uteri) is the narrow, cylindrical portion of the uterus. One end of the cervix protrudes into the top end of the vagina, and the other end is continuous with the corpus uteri. The inside of the cervix is lined with columnar epithelium. In the vagina, the cervix has an opening referred to as the external os (ostium externum). When one looks into the vagina, the part of the cervix that is visible is referred to as the 'portio'. Usually, (excluding during the ovulation) the uterus is blocked by a thick impermeable mucus. This mucosal plug can be found inside the cervix, and it protects the uterus against all kinds of infections. When a woman is pregnant, the cervix dilates shortly before labor. During the dilation of the cervix, the mucosal plug will come out (often accompanied by some blood). This is usually a signal that labor is about to commence. During the menstrual cycle, the cervix undergoes a few changes. Just after menstruation, the cervix is closed and positioned relatively low. In the period leading up to ovulation, the cervix rises, and the structure becomes softer. In this period, the cervix also opens slightly. After the ovulation, the cervix will return to its low position and the opening will close again. Cervical Cancer Cervical cancer is relatively common amongst women and is caused by an infection of Human Papillomavirus (abb. HPV). Cervical cancer can be detected at an early stage by examining a smear (via vaginal examination). If cervical cancer is detected at an early stage, treatment is effective and the woman is likely to be cured of this type of cancer.

Wednesday, 5 October 2011

VASA RECTA JUXTAMEDULLARY NEPHRON

In the blood supply of the kidney , the vasa recta renis (or straight arteries of kidney, or straight arterioles of kidney) form a series of straight capillaries (recta is from
the Latin for "straight") in the medulla. They lie parallel to the loop of Henle. These vessels branch off the efferent arterioles of juxtamedullary nephrons (those nephrons closest to the medulla), enter the medulla, and surround the loop of Henle. Histology On a slide, vasa recta can be distinguished
from the tubules of the loop of Henle by the presence of blood.[1] Function Each of the vasa recta has a hairpin turn in
the medulla and carries blood at a very
slow rate, two factors crucial in the
maintenance of countercurrent exchange that prevent washout of the concentration
gradients established in the renal medulla. [2] The maintenance of this concentration
gradient is one of the components
responsible for the kidney's ability to
produce concentrated urine. On the descending portion of the vasa
recta, NaCl and urea are reabsorbed into
the blood, while water is secreted. On the
ascending portion of the vasa recta, NaCl
and urea are secreted into the interstitium,
while water is reabsorbed. Nomenclature According to Terminologia Anatomica , the term "vasa recta renis" is an alternate
name for "arteriolae rectae renis", and a
separate term, venulae rectae renis, is used to identify the venous portion. However, other sources consider "vasa
recta renis" to refer to both the arterial and venous portions.[3] The "renis" is often omitted, but there do
exist two other structures with the same
name: vasa recta (intestines) (in the ileum and jejunum)[4] the straight portion of the seminiferous tubule, though this is usually called the tubuli recti. Pathology The slow blood flow in vasa recta makes
them a likely location of thrombosis in hypercoagulable states, or tissue loss[5] due to erythrocyte sickling in sickle cell disease. Ischemia that results may lead to renal papillary necrosis.

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VULVAL VESTIBULE

The Vulval vestibule (or "Vulvar vestibule") is a part of the vulva between the labia minora into which the urethral opening and the vaginal opening open. Its edge is marked by Hart's Line. The external urethral orifice (orificium
urethræ externum; urinary meatus) is placed about 2.5 cm behind the glans clitoridis and immediately in front of that of the vagina; it usually assumes the form of a short, sagittal cleft with slightly raised
margins. Nearby are the openings of the Skene's ducts. The vaginal orifice is a median slit below
and behind the opening of the urethra; its
size varies inversely with that of the hymen.

HYMEN

The hymen is a membrane that surrounds or partially covers the external vaginal opening. It forms part of the vulva , or external genitalia.[1][2] The size of the hymenal opening increases with age.
Although an often practiced method, it is
not possible to confirm with certainty that
a girl or woman is a virgin by examining her hymen.[2] In cases of suspected rape or child sexual abuse, a detailed examination of the hymen may be performed, but the
condition of the hymen alone is often
inconclusive. In younger children, a torn
hymen will typically heal very quickly. In
adolescents, the hymenal opening does
extend from natural causes and variation in shape and appearance increases.[1] In children, although a common appearance
of the hymen is crescent-shaped, many variations are possible.[1] After a woman gives birth, she may be left with remnants of the hymen, called carunculae
myrtiformes, or the hymen may be completely absent.[3] Development The genital tract develops during embryogenesis, from the third week of
gestation to the second trimester, and the
hymen is formed following the vagina. At week seven, the urorectal septum forms
and separates the rectum from the
urogenital sinus. At week nine, the müllerian ducts move
downwards to reach the urogenital sinus,
forming the uterovaginal canal and
inserting into the urogenital sinus. At week 12, the müllerian ducts fuse to
create a primitive uterovaginal canal called
unaleria At month 5, the vaginal canalization is
complete and the fetal hymen is formed
from the proliferation of the sinovaginal
bulbs (where müllerian ducts meet the
urogenital sinus), and becomes perforate
before or shortly after birth. In newborn babies, still under the influence
of the mother's hormones, the hymen is thick, pale pink, and redundant (folds in on
itself and may protrude). For the first two
to four years of life, the infant produces hormones that continue this effect.[4] Their hymenal opening tends to be annular (circumferential).[5] Resorption Past neonatal stage, the diameter of the
hymenal opening (measured within the
hymenal ring) has been proposed to be
approximately 1 mm for each year of age. [6] In children, to make this measurement, a doctor may place a Foley catheter into the vagina and inflate the balloon behind
the hymen to stretch the hymenal margin
and allow for a better examination. In the
normal course of life, the hymenal opening
can also be enlarged by tampon or menstrual cup use, pelvic examinations with a speculum, regular physical activity or sexual intercourse.[1] Once a girl reaches puberty, the hymen tends to become so
elastic that it is not possible to determine
whether a woman uses tampons or not by
examining her hymen. In one survey, only
43% of women reported bleeding the first
time they had intercourse, indicating that the hymens of a majority of women are sufficiently opened. [1][4] The hymen is most apparent in young girls:
At this time, their hymen is thin and less
likely to be redundant, that is to protrude or fold over on itself. [7] In instances of suspected child abuse, doctors use the clock face system to describe the hymenal opening. The 12 o'clock position is below
the urethra, and 6 o'clock is towards the anus, with the patient lying on her back. [8] Infants' hymenal openings tend to be
redundant (sleeve-like, folding in on itself), and may be ring-shaped.[8] By the time a girl reaches school age, this
hormonal influence has ceased, and the
hymen becomes thin, smooth, delicate, and
nearly translucent. It is also very sensitive to touch; a physician who must swab the
area should avoid the hymen and swab the outer vulval vestibule instead.[4] Prepubescent girls' hymenal openings
come in many shapes, depending on
hormonal and activity level, the most
common being crescentic (posterior rim):
no tissue at the 12 o'clock position;
crescent-shaped band of tissue from 1–2 to 10–11 o'clock, at its widest around 6
o'clock. From puberty onwards, depending
on estrogen and activity levels, the hymenal tissue may be thicker, and the
opening is often fimbriated or erratically shaped.[5] After giving birth, the vaginal opening
usually has nothing left but hymenal tags
(carunculae myrtiformes) and is called
"parous introitus". Anatomic anomalies Various types of hymen Anomalies of the female reproductive tract
can result from agenesis or hypoplasia, canalization defects, lateral fusion and
failure of resorption, resulting in various complications.[6] Imperforate:[9][10] hymenal opening nonexistent; will require minor surgery
if it has not corrected itself by puberty
to allow menstrual fluids to escape. Cribriform, or microperforate:
sometimes confused for imperforate,
the hymenal opening appears to be
nonexistent, but has, under close
examination, small openings. Septate: the hymenal opening has one
or more bands extending across the
opening. Hymenorrhaphy Main article: Hymenorrhaphy In some cultures, an intact hymen is highly
valued at marriage mainly to show virginity.[11][12][13] Some women undergo hymenoplasty, a restoration of their hymen for this reason.[13][14] Womb fury In the sixteenth and seventeenth centuries,
medical researchers used the presence of
the hymen, or lack thereof, as founding
evidence of physical diseases such as
"womb-fury" ( hysteria). If not cured, womb-fury would, according to these early doctors, result in death.

LABIA MINORA

The labia minora (singular: labium minus), also known as the inner labia, inner lips, or nymphae,[1] are two flaps of skin on either side of the human vaginal opening, situated between the labia majora (outer labia, or outer lips). Inner lips vary widely
in size, colour, and shape from woman to
woman. The inner lips extend from the clitoris obliquely downward, laterally, and
backward on either side of the vulval vestibule, ending between the bottom of the vulval vestibule and the outer lips. The posterior ends (bottom) of the inner lips are usually joined across the middle line by
a fold of skin, named the frenulum labiorum pudendi or fourchette. On the front, each lip divides into two
portions. The upper part of each lip passes
above the clitoris to meet the upper part of
the other lip—which will probably be a
little larger or smaller—forming a fold
which overhangs the glans clitoridis; this fold is named the preputium clitoridis. The lower part passes beneath the glans
clitoridis and becomes united to its under
surface, forming, with the inner lip of the
opposite side, the frenulum clitoridis. On the opposed surfaces of the labia
minora are numerous sebaceous hair follicles. Size and shape In or around 2004, researchers from the
Department of Gynaeology, Elizabeth
Garret Anderson Hospital in London,
measured the labia and other genital
structures of 50 women from the age of 18
to 50, with a mean age of 35.6. The results were:[2] Measuring Range Mean [SD] Clitoral length (mm) 5–35 19.1
[8.7] Clitoral glans width (mm) 3–10 5.5 [1.7] Clitoris to urethra (mm) 16–45 28.5
[7.1] Labia majora length (cm) 7.0–12.0 9.3 [1.3] Labia minora length (mm) 20–100 60.6
[17.2] Labia minora width
(mm) 7–50 21.8
[9.4] Perineum length (mm) 15–55 31.3
[8.5] Vaginal length (cm) 6.5–12.5 9.6 [1.5] Tanner stage (n) IV 4 ditto V 46 Colour of genital area compared with
surrounding skin (n) Same 9 ditto Darker 41 Rugosity of labia (n) Smooth 14 ditto Moderate 34 ditto Marked 2

LABIA MAJORA

The labia majora (singular: labium majus) are two prominent longitudinal cutaneous folds that extend downward and backward from the mons pubis to the perineum and form the lateral boundaries of the pudendal cleft, which contains the labia minora, interlabial sulci, clitoral hood, clitoral glans, frenulum clitoridis, the Hart's Line, and the vulval vestibule , which contains the external openings of the urethra and the vagina. Each labium majus has two surfaces, an
outer, pigmented and covered with strong,
crisp hairs; and an inner, smooth and beset
with large sebaceous follicles. Between the two there is a considerable
quantity of areolar tissue, fat, and a tissue resembling the dartos tunic of the scrotum, besides vessels, nerves, and glands. The Labia Majora are thicker in front,
where they form by their meeting the anterior commisure of the labia majora. Posteriorly they are not really joined, but
appear to become lost in the neighboring
integument, ending close to — and nearly
parallel with — each other. Together with the connecting skin
between them, they form the posterior commisure of the labia majora or posterior boundary of the pudendum. The interval between the posterior
commissure of the labia majora and the anus, from 2.5 to 3 cm. in length, constitutes the perineum. The labia majora correspond to the scrotum in the male. Between the labia majora and the inner thighs are the labiocrural folds. Between the labia majora and labia
minora are the interlabial sulci.

MONS PUBIS

In human anatomy or in mammals in general, the mons pubis (Latin for "pubic mound"), also known as the mons veneris (Latin, mound of Venus) or simply the mons, is the adipose tissue lying above the pubic bone of adult females, anterior to the pubic symphysis . The mons pubis forms the anterior portion of the vulva . The size of the mons pubis varies with the
general level of hormone and body fat.
After puberty it is covered with pubic hair and enlarges. In human females this
mound is made of fat and is supposed to be
larger. It provides protection of the pubic
bone during intercourse. In humans, the mons pubis divides into the labia majora (literally "larger lips") on either side of the furrow, known as the pudendal cleft, that surrounds the labia minora, clitoris, vaginal opening, and other structures of the vulval vestibule . The fatty tissue of the mons pubis is sensitive to
estrogen, causing a distinct mound to form
with the onset of puberty. This pushes the
forward portion of the labia majora out
and away from the pubic bone.

FALLOPIAN TUBE

The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges (singular salpinx) are two very fine tubes lined with ciliated epithelia, leading from the ovaries of female mammals into the uterus, via the utero-tubal junction. In non- mammalian vertebrates, the equivalent structures are the oviducts. Anatomy and histology In a woman's body the tube allows passage of the egg from the ovary to the uterus. Its different segments are (lateral to medial): the infundibulum with its associated fimbriae near the ovary, the ampullary region that represents the major portion of the lateral tube, the isthmus which is the narrower part of the tube that links to the uterus, and the interstitial (also intramural) part that transverses the uterine musculature. The tubal ostium is the point where the tubal canal meets the peritoneal cavity, while the uterine opening of the Fallopian tube is the entrance into the uterine cavity, the utero- tubal junction. There are two types of cells within the simple columnar epithelium of the Fallopian tube (oviduct). Ciliated cells predominate throughout the tube, but are most numerous in the infundibulum and ampulla. Estrogen increases the production of cilia on these cells. Interspersed between the ciliated cells are peg cells, which contain apical granules and produce the tubular fluid. This fluid contains nutrients for spermatozoa, oocytes, and zygotes. The secretions also promote capacitation of the sperm by removing glycoproteins and other molecules from the plasma membrane of the sperm. Progesterone increases the number of peg cells, while estrogen increases their height and secretory activity. Tubal fluid flows against the action of the ciliae, that is toward the fimbrated end. Function in fertilization When an ovum is developing in an ovary, it is encapsulated in a sac known as an ovarian follicle. On maturity of the ovum, the follicle and the ovary's wall rupture, allowing the ovum to escape. The egg is caught by the fimbriated end and travels to the ampulla where typically the sperm are met and fertilization occurs; the fertilized ovum, now a zygote, travels towards the uterus aided by activity of tubal cilia and activity of the tubal muscle. After about five days the new embryo enters the uterine cavity and implants about a day later. The release of a mature egg does not alternate between the two ovaries and seems to be random. After removal of an ovary, the remaining one produces an egg every month. [1] Occasionally the embryo implants into the Fallopian tube instead of the uterus, creating an ectopic pregnancy, commonly known as a "tubal pregnancy". Patency testing While a full testing of tubal functions in patients with infertility is not possible, testing of tubal patency is important as tubal obstruction is a major cause of infertility. A hysterosalpingogram will demonstrate that tubes are open when the radio-opaque dye spills into the uterine cavity. Tubal insufflation is a standard procedure for testing patency. During surgery the condition of the tubes may be inspected and a dye such as methylene blue can be injected into the uterus and shown to pass through the tubes when the cervix is occluded. As tubal disease is often related to Chlamydia infection, testing for Chlamydia antibodies has become a cost- effective screening device for tubal pathology.[2] Embryology and homology Embryos have two pairs of ducts to let gametes out of the body; one pair (the Müllerian ducts) develops in females into the Fallopian tubes, uterus and vagina, while the other pair (the Wolffian ducts) develops in males into the epididymis and vas deferens. Normally, only one of the pairs of tubes will develop while the other regresses and disappears in utero. The homologous organ in the male is the rudimentary appendix testis. Pathology Pelvic inflammatory disease can strike the fallopian tubes. This might cause a Fallopian tube obstruction. Fallopian tube cancer is a rare neoplasm that can arise from the epithelial lining of the Fallopian tube. This cancer is sometimes misdiagnosed as ovarian cancer.[3] However, treatment of both ovarian and Fallopian tube cancer is similar. Surgery The surgical removal of a Fallopian tube is called a salpingectomy. To remove both sides is a bilateral salpingectomy. An operation that combines the removal of a Fallopian tube with removal of at least one ovary is a salpingo-oophorectomy. An operation to restore a fallopian tube obstruction is called a tuboplasty. Etymology and nomenclature They are named after their discoverer, the 16th century Italian anatomist, Gabriele Falloppio. Though the name 'Fallopian tube' is eponymous, some texts spell it with a lower case 'f' from the assumption that the adjective 'fallopian' has been absorbed into modern English as the de facto name for the structure. The Greek word salpinx (σαλπιγξ) means "trumpet".

BLADDER

The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow [1]muscular, and distensible (or elastic) organ, the bladder sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra. Bladders occur throughout much of the animal kingdom, but are very diverse in form and in some cases are not homologous with the urinary bladder in humans. The human urinary bladder is derived in embryo from the urogenital sinus and, it is initially continuous with the allantois. In males, the base of the bladder lies between the rectum and the pubic symphysis. It is superior to the prostate, and separated from the rectum by the rectovesical excavation . In females, the bladder sits inferior to the uterus and anterior to the vagina; thus, its maximum capacity is lower than in males. It is separated from the uterus by the vesicouterine excavation . In infants and young children, the urinary bladder is in the abdomen even when empty. [2] Detrusor muscle The detrusor muscle is a layer of the urinary bladder wall made of smooth muscle fibers arranged in spiral, longitudinal, and circular bundles. When the bladder is stretched, this signals the parasympathetic nervous system to contract the detrusor muscle. This encourages the bladder to expel urine through the urethra. For the urine to exit the bladder, both the autonomically controlled internal sphincter and the voluntarily controlled external sphincter must be opened. Problems with these muscles can lead to incontinence. The urinary bladder usually holds 300-350 ml of urine. As urine accumulates, the rugae flatten and the wall of the bladder thins as it stretches, allowing the bladder to store larger amounts of urine without a significant rise in internal pressure.[3] The urge to urinate usually starts when the bladder reaches around 25% of its working volume. At this stage it is easy for the subject, if desired, to resist the urge to urinate. As the bladder continues to fill, the desire to urinate becomes stronger and harder to ignore. Eventually, the bladder will fill to the point where the urge to urinate becomes overwhelming, and the subject will no longer be able to ignore it. If the amount of urine reaches 100% of the urinary bladder's capacity, the voluntary sphincter becomes involuntary, and the urine will be ejected instantly.[citation needed] Since the urinary bladder has a transitional epithelium, it does not produce mucus.[4] Fundus The fundus of the urinary bladder is the base of the bladder, formed by the posterior wall. It is lymphatically drained by the external iliac lymph nodes. The peritoneum lies superior to the fundus. Urination frequency Urination frequency refers to the number of times someone urinates. Males with an enlarged prostate urinate more frequently.[citation needed] Innervation The bladder receives motor innervation from both sympathetic fibers, most of which arise from the hypogastric plexuses and nerves, and parasympathetic fibers, which come from the pelvic splanchnic nerves and the inferior hypogastric plexus. [5] Sensation from the bladder is transmitted to the central nervous system (CNS) via general visceral afferent fibers (GVA). GVA fibers on the superior surface follow the course of the sympathetic efferent nerves back to the CNS, while GVA fibers on the inferior portion of the bladder follow the course of the parasympathetic efferents. [5] Disorders Main article: Urinary bladder disease A diverticulum of the bladder Disorders of or related to the bladder include: Bladder cancer Bladder exstrophy Bladder infection Bladder spasm Bladder sphincter dyssynergia , a condition in which the sufferer cannot coordinate relaxation of the urethra sphincter with the contraction of the bladder muscles Bladder stones Cystitis Hematuria, or presence of blood in the urine, is a reason to seek medical attention without delay, as it is a symptom of bladder cancer as well as bladder and kidney stones Interstitial Cystitis Overactive bladder , a condition that affects a large number of people Urinary incontinence Urinary retention

PUBIC BONE

For the bone in many mammals often called the penis bone, see baculum In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis. It is covered by a layer of fat, which is covered by the mons pubis. It is divisible into a body, a superior ramus and an inferior ramus. The body forms one-fifth of the acetabulum, contributing by its external surface both to the lunate surface and the acetabular fossa. Its internal surface enters into the formation of the wall of the lesser pelvis and gives origin to a portion of the obturator internus. In the female, the pubic bone is anterior to the urethral sponge. The left and right hip bones join at the pubic symphysis . The pubis is the lower limit of the suprapubic region. In dinosaurs The clade Dinosauria is divided into the Saurischia and Ornithischia based on hip structure, including importantly that of the pubis.[1] Ornithischian pelvic structure (left side) Saurischian pelvic structure (left side).

G-SPOT

The G-Spot (4) is located one to three inches into the vagina, at the side of the urethra (6) and the urinary bladder (2). The Gräfenberg Spot, often called the G- Spot, is a bean-shaped[1] area of the vagina. Many women report that it is an erogenous zone which, when stimulated, can lead to strong sexual arousal, powerful orgasms and female ejaculation.[2] The Gräfenberg Spot is typically located one to three inches (2.5 to 7.6 cm) up the front (anterior) vaginal wall between the vaginal opening and the urethra[3] and is a sensitive area that may be part of the female prostate.[4] Although the G-Spot has been studied since the 1940s,[5] disagreement persists over its existence as a distinct structure, definition and location.[6][7] A 2009 British study concluded that its existence is unproven and subjective, based on questionnaires and personal experience.[8] It is also hypothesised that the G-Spot is an extension of the clitoris and that this is the cause of vaginal orgasms.[9][10] Other studies, using ultrasound, have found physiological evidence of the G-Spot in women who report having orgasms during intercourse.[11][12] Sexual psychologists are concerned that women may consider themselves to be dysfunctional if they cannot find their G- Spot.[13] Women have undergone a plastic surgery procedure called G-Spot amplification to enhance its sensitivity. [5] Origin The term "G-Spot" was coined by Addiego et al. in 1981,[14] after the German gynecologist Ernst Gräfenberg,[15] even though his 1940s research was dedicated to urethral stimulation and not internal vaginal wall stimulation. The concept entered popular culture after the publication of The G Spot and Other Recent Discoveries About Human Sexuality by Ladas et al. in 1982,[2] but it was criticized immediately by leading gynecologists. [1] They denied its existence as it is not easily found if not aroused and autopsy studies missed this. After the G-Spot was demonstrated for their observation they changed their minds.[5] An anonymous questionnaire was distributed to 2350 professional women in the United States and Canada with a subsequent 55% return rate. Of these respondents, 40% reported having a fluid release (ejaculation) at the moment of orgasm. Further, 82% of the women who reported the sensitive area (Gräfenberg Spot) also reported ejaculation with their orgasms. A number of variables were associated with this perceived existence of female ejaculation.[16] While not disputing vaginal responsiveness to stimulation, gynecologists and doctors continue to be skeptical of the existence of a distinct anatomical feature in the G-Spot rub zone.[1][7][17] Female prostate See also: Skene's gland and Urethral sponge In 2001, the Federative Committee on Anatomical Terminology accepted female prostate as an accurate term for the Skene's gland found in the G-Spot area along the walls of the urethra.[4] The male prostate is biologically homologous to the female G-Spot, which was first hypothesized by Regnier de Graaf in 1672 where he observed that the secretions (female ejaculation) by the women's G- Spot "lubricates their sexual parts in agreeable fashion during coitus."[4] The prostate in men has been unofficially called the male G-Spot because it can also be used as an erogenous zone.[18] It is located where the rectum joins the colon, about 50 mm (2 in) from the anus, and when aroused it is a walnut-shaped swelling. Links between G-Spot sensitivity and female ejaculation led to the idea that non- urine female ejaculate may originate from the Skene's gland. Tissue examination showed 15 prostate-specific antigens in the gland,[19] leading to a trend of calling the Skene's glands the female prostate.[20] Consequently, it has been argued that the G-Spot is a system of glands and ducts located within the anterior (front) wall of the vagina about one centimeter from the surface.[21] A similar approach has linked the G-Spot with the urethral sponge.[22] The enzyme PDE5 (involved with erectile dysfunction) has been associated with the G-Spot area.[23] Several researchers consider the connection between the Skene's gland and the G-Spot to be weak.[6][24] They contend that Skene's gland does not appear to have receptors for touch stimulation, and that there is no direct evidence for its involvement. [25] Sexual stimulation and studies The G-Spot is typically located about 50 to 80 mm (2 to 3 in) inside the vagina, on the front wall.[5] For some women, stimulating the G-Spot creates a more intense orgasm than clitoral stimulation.[3][26] The G-Spot needs direct stimulation, especially with firm moves and constant pressure as it is ~1 cm below the surface.[21] Stimulating the G-Spot through sexual penetration, especially in the missionary position,[5] is difficult to achieve because of the special angle at which penetration must occur. It is claimed that the best G-Spot stimulation is achieved by using both manual stimulation and sexual intercourse.[3] Methodology Two primary methods have been used to define and locate the G-Spot as a sensitive area in the vagina:[6] self-reported levels of arousal during stimulation stimulation of the G-Spot leads to female ejaculation Studies using ultrasound have also been used to identify physiological differences between women [11] and changes to the G- Spot region during sex.[12] Findings In a published case study of one woman, it was reported that stimulation of the anterior vaginal wall made the area grow by fifty percent and that self-reported levels of arousal/orgasm were "deeper" when the G-Spot was stimulated. [14] Another study examined eleven women by palpating the entire vagina in a clockwise fashion, and reported a specific response to stimulation of the anterior vaginal wall in four of the women. [27] Researchers at the University of L'Aquila have found, using ultrasonography, that women who experience vaginal orgasm are statistically more likely to have thicker tissue in the anterior vaginal wall. [11] The researchers believe these findings make it possible for women to have a rapid test to confirm whether or not they have a G-Spot. [28] A French study in late 2009 examined a small number of women with ultrasound as they had intercourse, by examining changes in the vagina they found physiological evidence of the G-Spot. The findings are under review by the Journal of Sexual Medicine.[12] There is some research suggesting that G- Spot and clitoral orgasms are of the same origin. Masters and Johnson were the first to determine that the clitoral structures surround and extend along and within the labia, determining that all orgasms are of clitoral origin.[9] Dr. Tim Spector hypothesizes thicker tissue in the G-Spot area may be part of the clitoris and is not a separate erogenous zone.[13] Supporting these conclusions is a 2005 study investigating the size of the clitoris – it found clitoral tissue extends considerably inside the vagina. This discovery indicates clitoral and vaginal orgasms are produced by the same internal source.[10] The main researcher of the studies, Australian urologist Dr. Helen O'Connell, asserts that this interconnected relationship is the physiological explanation for the conjectured G-Spot and experience of vaginal orgasm, taking into account the stimulation of the internal parts of the clitoris during vaginal penetration. "The vaginal wall is, in fact, the clitoris," said O'Connell. "If you lift the skin off the vagina on the side walls, you get the bulbs of the clitoris – triangular, crescental masses of erectile tissue."[10] Criticism G-Spot proponents are criticized for giving too much credence to anecdotal evidence, and for questionable investigative methods: for instance, the studies which have yielded positive evidence for a precisely located G-Spot involve small participant samples.[6] Scientific examinations of vaginal wall innervation have generally shown that there is no single area with a greater density of nerve endings. [6] A recent study of 110 biopsy specimens drawn from 21 women concluded with the absence of a vaginal locus with greater nerve density. [29] However, while neither the area of the anterior vaginal wall where the G-Spot is said to be located nor the Skene's gland appear to possess them, the urethral sponge, which is thought by some to be homologous to the G-Spot, does contain sensitive nerve endings as well as erectile tissue. It should also be noted that sensitivity is not determined by neuron density alone: other factors include the branching patterns of neuron terminals and cross or collateral innervation of neurons. [30] The existence of the G-Spot was questioned by a team at King's College London in late 2009. They acquired the largest sample size to date of 1,800 women – who are pairs of twins – and found they did not report a similar G-Spot in a questionnaire, suggesting its existence is subjective.[31] Study co-author Dr. Andrea Burri believes: "It is irresponsible to claim the existence of an entity that has never been proven and pressurise women and men too."[8] Burri also stated one of the reasons for the research was to remove feelings of "inadequacy or underachievement" for women who feared they lacked a G-Spot. [32] Dr. Whipple dismissed the findings, commenting that twins have different sexual partners and techniques, and that the study did not properly account for lesbian or bisexual women.[31] Sexual psychologists are concerned about the promotion of the G-Spot, as it could lead to women feeling "dysfunctional" if they do not experience it. Dr. Petra Boynton, a British scientist who has written extensively on this debate, [33] states:[13] We're all different. Some women will have a certain area within the vagina which will be very sensitive, and some won't — but they won't necessarily be in the area called the G-Spot. If a woman spends all her time worrying about whether she is normal, or has a G-Spot or not, she will focus on just one area, and ignore everything else. It's telling people that there is a single, best way to have sex, which isn't the right thing to do. The Journal of Sexual Medicine is planning a debate and publications from both sides of the G-Spot issue.[31] Sex toys One of the most common sex toys used in G-Spot stimulation is the specially designed G-Spot vibrator. This is a phallus-like vibrator that has a curved tip which makes G-Spot stimulation very easy. The head of the G-Spot vibrator has a special form and it is a little curved in order to ease the stimulation of the G-Spot. The level of penetration when using this sex toy depends on every woman because the physiology is not the same in two individuals. The effect of the G-Spot stimulation, no matter which way this is done, may be enhanced by stimulation of the other erogenous zones in a woman's body. These may include the clitoris and labia.[34] These toys are made from the same materials as regular vibrators, including silicone, jelly, rubber or any combination of them.

CLITORIS

The clitoris ( i/ˈklɪtərɨs/, i/klɨˈtɔərɨs/, or UK /ˈklaɪtɒrɨs/) is a sexual organ that is present only in female mammals. In humans, the visible button-like portion is located near the anterior junction of the labia minora, above the opening of the urethra and vagina. Unlike the penis, which is homologous to the clitoris, the clitoris does not contain the distal portion of the urethra. The only known exception to this is in the Spotted Hyena. In this species, the urogenital system is unique in that the female urinates, mates and gives birth via an enlarged, erectile clitoris, known as a pseudo-penis.[1] In humans, the clitoris is the most sensitive erogenous zone of the female, the stimulation of which may produce sexual excitement and clitoral erection; its continuing stimulation may produce sexual pleasure and orgasm, and is considered the key to females' sexual pleasure. [2][3] Pronunciation and etymology The plural forms are clitorises in English and clitorides in Latin. In slang, it is sometimes abbreviated as clit, which originated in the 1950s. The OED suggests that the pronunciation /ˈklaɪtɒrɨs/ is also used in the United Kingdom, and gives the likely etymology as coming from the Greek κλειτορίς, kleitoris, perhaps derived from the verb κλείειν, kleiein, to shut. The Online Etymology Dictionary states that the etymology of this diminutive is uncertain. Possible etymological candidates are a Greek word meaning "key", "latch", "hook"; a Greek verb meaning "to touch or titillate lasciviously", "to tickle" (the clitoris is called in German slang der Kitzler, "the tickler"), although this verb is more likely derived from "clitoris"; and a Greek word meaning "side of a hill", from the same root as "climax".[4] Its Latin genitive is clitoridis, as in "glans clitoridis". Structure The head or glans of the clitoris is roughly the size and shape of a pea, although it can be significantly larger or smaller. Human vulva Human vulva stretched to show externally-visible features of the clitoris in relation to other components: 1. Clitoral hood (prepuce); 2. Clitoral glans; 3. Urethral orifice; 4. Vulval vestibule; 5. Labia minora; 6. Vaginal opening; 7. Labia majora (hair removed); 8. Perineum MeSH Vulva Dorlands/Elsevier vulva The clitoris is a complex structure, with both external and internal components. Projecting at the front of the labial commissure where the edges of the outer lips (labia majora) meet at the base of the pubic mound is the clitoral hood (prepuce), which in full or part covers the head (clitoral glans). Following from the head back and up along the shaft, it is found that this extends up to several centimeters before reversing direction and branching. The resulting branched shape forms an inverted "V", extending as a pair of "legs" known as the clitoral crura formed of the corpora cavernosa. The clitoral crura are concealed behind the labia minora, and terminate with attachment to the pubic arch (according to some),[5] or follow interior to the labia minora to meet at the fourchette (according to others).[2] Associated are the urethral sponge, clitoral/vestibular bulbs, perineal sponge, a network of nerves and blood vessels, suspensory ligaments, muscles and pelvic diaphragm.[6] There is considerable variation in how much of the clitoris protrudes from the hood and how much is covered by it, ranging from complete, covered invisibility to full, protruding visibility. An article published in the Journal of Obstetrics and Gynecology in July 1992 states that the average width of the clitoral glans lies within the range of 2.5 to 4.5 millimetres (0.098 to 0.18 in), indicating that the average size is smaller than a pencil-top eraser. Recent discoveries about the size of the clitoris show that clitoral tissue extends some considerable distance inside the body, around the vagina. It is now clear that clitoral tissue is far more widespread than the small visible part most people associate with the word. [3] There is no identified correlation between the size of a clitoris and a woman's age, height, weight, use of hormonal contraceptives, or being post-menopausal. Sexual stimulation Click here to see a video showing clitoris becoming engorged with blood Research shows most women achieve orgasm only through clitoral stimulation.[3] [7][8][9][10][11]Masters and Johnson were the first to determine that the clitoral structures surround and extend along and within the labia. They observed that both clitoral and vaginal orgasms had the same stages of physical response, and argued that clitoral stimulation is the primary source of both kinds of orgasms.[7] Supporting these findings is a 2005 study which investigated the size of the clitoris; Australian urologist Dr. Helen O'Connell, while using MRI technology, noted a direct relationship between the legs or roots of the clitoris and the erectile tissue of the clitoral bulbs and corpora, and the distal urethra and vagina.[3] O'Connell asserts that this interconnected relationship is the physiological explanation for the conjectured G-Spot and experience of vaginal orgasm, taking into account the stimulation of the internal parts of the clitoris during vaginal penetration.[3] "The vaginal wall is, in fact, the clitoris," said O'Connell. "If you lift the skin off the vagina on the side walls, you get the bulbs of the clitoris – triangular, crescental masses of erectile tissue." The idea was that the clitoris is more than just its glans – the "little hill".[3] Pulled-out clitoris During sexual arousal and during orgasm, the clitoris and the whole of the genitalia engorge and change color as these erectile tissues fill with blood, and the individual experiences vaginal contractions. Masters and Johnson documented the sexual response cycle, which has four phases and is still the clinically accepted definition of the human orgasm. More recent research has determined that some can experience a sustained intense orgasm through stimulation of the clitoris and remain in the orgasmic phase for much longer than the original studies indicated, evidenced by genital engorgement, color changes, and vaginal contractions.[12] Embryonic development Stages in the development of clitoris During the development of an embryo , at the time of development of the urinary and reproductive organs, the previously undifferentiated genital tubercle develops into either a clitoris or penis, along with all other major organ systems, making them homologous.[6] The clitoris is formed from the same tissues that would have become the glans and upper shaft of a penis if the embryo had been exposed to “male” hormones. Changes in appearance of male and female embryos begin roughly eight weeks after conception. By birth, the genital structures have developed into the female reproductive system .[13] Embryo sex based on external genitalia is apparent to a doctor at the end of the 14th menstrual week, and the sex can usually be identified by an ultrasound after 16 to 18 menstrual weeks.[14] A condition that can develop from naturally occurring or deliberate exposure to higher than average levels of testosterone is clitoromegaly. Recognition of existence The clitoris has been thought of as "discovered" and "rediscovered" through empirical documentation by male scholars repeatedly over the centuries. [15] Over a period of more than 2,500 years, some have considered the clitoris and the penis equivalent in all respects except their arrangement.[2]Realdo Colombo (also known as Matteo Renaldo Colombo) was a lecturer in surgery at the University of Padua, Italy, and in 1559 he published a book called De re anatomica[16] in which he described the "seat of woman's delight". Disregarding females' awareness of their own bodies, Colombo concluded, "Since no one has discerned these projections and their workings, if it is permissible to give names to things discovered by me, it should be called the love or sweetness of Venus."[17] Colombo's claim was disputed by his successor at Padua, Gabriele Falloppio (who discovered the fallopian tube), who claimed that he was the first to discover the clitoris. Caspar Bartholin, a 17th- century Danish anatomist, dismissed both claims, arguing that the clitoris had been widely known to medical science since the second century. Indeed, Hippocrates used the term columella (little pillar). Avicenna named the clitoris the albatra or virga (rod). Albucasis, an Arabic medical authority, named it tentigo (tension). It was also known to the Romans, who named it (vulgar slang) landica.[18] This cycle of suppression and discovery continued, notably in the work of Regnier de Graaf (Tractatus de Virorum Organis Generationi Inservientibus, De Mulierum Organis Generationi Inservientibus Tractatus Novus) in the 17th century and Georg Ludwig Kobelt (Die männlichen und weiblichen Wollustorgane des Menschen und einiger Säugetiere) in the 19th. De Graaf criticised Columbo's claims for this. (Harvey, Laqueur). The full extent of the clitoris was alluded to by Masters and Johnson in 1966, but in such a muddled fashion that the significance of their description became obscured. In 1981, the Federation of Feminist Women's Health Clinics (FFWHC) continued this process with anatomically precise illustrations.[2] Today, MRI complements these efforts, as it is both a live and multiplanar method of examination.[3] Female genital mutilation Main article: Female genital mutilation The clitoris may be partially or totally removed during female genital mutilation (FGM), also known as a clitoridectomy, or female circumcision. This is carried out in several countries in Africa, and to a lesser extent in the Middle East and Southeast Asia, on girls from a few days old to the age of 15.[19]Amnesty International estimates that over two million FGM procedures are performed every year. [20] Female genital modification Main article: Genital modification and mutilation In various cultures, the clitoris is sometimes pierced directly. In U.S. body modification culture, it is actually extremely rare for the clitoral shaft itself to be pierced, as of the already few people who desire the piercing, only a small percentage are anatomically suited for it; furthermore, most piercing artists are reluctant to attempt such a delicate procedure. Some styles, such as the Isabella, do pass through the clitoris but are placed deep at the base, where they provide unique stimulation; they still require the proper genital build, but are more common than shaft piercings. Additionally, what is (erroneously) referred to as a "clit piercing" is almost always the much more common (and much less complicated) clitoral hood piercing. Enlargement may be intentional or unintentional. Those taking hormones and/ or other medications as part of female-to- male transition usually experience dramatic clitoral growth; individual desires (and the difficulties of surgical phalloplasty) often result in the retention of the original genitalia, the enlarged clitoris analogous to a penis as part of the transition. However, the clitoris cannot reach the size of most cissexual men's penises through hormones. Surgery to add function to the clitoris, such as metoidioplasty or clitoral release, are alternatives to phalloplasty (construction of a penis) which permit retention of sexual sensation in the clitoris. On the other hand, use of anabolic steroids by bodybuilders and other athletes can result in significant enlargement of the clitoris in concert with other masculinizing effects on their bodies. Temporary engorgement results from suction pumping, practiced to enhance sexual pleasure or for aesthetic purposes.

URETHRA

In anatomy, the urethra (from Greek οὐρήθρα - ourethra) is a tube that connects
the urinary bladder to the genitals for the removal of fluids out of the body. In males,
the urethra travels through the penis, and carries semen as well as urine. In females, the urethra is shorter and emerges above
the vaginal opening. The external urethral sphincter is a striated muscle that allows voluntary control over urination. Anatomy Female urethra In the human female, the urethra is about
1.5–2 inches (4–5 cm) long and exits the
body between the clitoris and the vagina, extending from the internal to the external
urethral orifice. It is placed behind the
symphysis pubis, embedded in the anterior
wall of the vagina, and its direction is
obliquely downward and forward; it is
slightly curved with the concavity directed forward. Its lining is composed of stratified
squamous epithelium, which becomes
transitional near the bladder. The urethra
consists of three coats: muscular, erectile,
and mucous, the muscular layer being a
continuation of that of the bladder. Between the superior and inferior fascia of
the urogenital diaphragm, the female
urethra is surrounded by the Sphincter urethrae (urethral sphincter). Somatic (conscious) innervation of the external urethral sphincter is supplied by the pudendal nerve. The uro-genital sinus may be divided into three component parts. The
first of these is the cranial portion which is
continuous with the allantois and forms
the bladder proper. The pelvic part of the
sinus forms the prostatic urethra and
epithelium as well as the membranous urethra and bulbo urethral glands in the
male and the membranous urethra and
part of the vagina in females. The area
above and on both sides of the female urethra is thought by some[who?] to be sexually sensitive and is sometimes
referred to as the U-spot or urethral erogenous zone. Male urethra In the human male, the urethra is about 8
inches (20 cm) long and opens at the end of
the penis. The urethra provides an exit for urine as well as semen during ejaculation. The urethra is divided into four parts in
men, named after the location: Region Description Epithelium pre-prostatic
urethra This is the
intramural part
of the urethra
and varies
between 0.5
and 1.5 cm in length
depending on
the fullness of
the bladder. Transitional prostatic
urethra Crosses through
the prostate gland. There are several
openings: (1)
the ejaculatory duct receives sperm from the vas deferens and ejaculate
fluid from the seminal vesicle, (2) several prostatic ducts where fluid
from the prostate enters and contributes
to the
ejaculate, (3)
the prostatic utricle, which is merely an
indentation.
These openings
are collectively
called the
verumontanum. Transitional membranous
urethra A small (1 or
2 cm) portion
passing through
the external urethral
sphincter. This is the
narrowest part
of the urethra.
It is located in
the deep perineal pouch. The bulbourethral
glands (Cowper's
gland) are
found posterior
to this region
but open in the spongy urethra. Pseudostratified
columnar spongy
urethra (or penile
urethra) Runs along the
length of the
penis on its
ventral
(underneath)
surface. It is about 15–16 cm
in length, and
travels through
the corpus spongiosum. The ducts from
the urethral gland (gland of Littre) enter
here. The
openings of the bulbourethral
glands are also found here.[1] Some textbooks
will subdivide
the spongy
urethra into
two parts, the
bulbous and pendulous
urethra. Pseudostratified
columnar – proximally, Stratified
squamous – distally The length of a male's urethra, and the fact
it contains a prominent bend, makes catheterization more difficult. The integrity of the urethra can be determined
by a procedure known as retrograde urethrogram. Histology The epithelium of the urethra starts off as transitional cells as it exits the bladder. Further along the urethra there are stratified columnar cells, then stratified squamous cells near the external urethral orifice. There are small mucus-secreting urethral glands, that help protect the epithelium
from the corrosive urine. Length of the urethrae The female urethra is about 4 cm in length. [2] There is inadequate data for the typical length of the male urethra, however a
study of 109 men showed an average
length of 22.3 cm (SD = 2.4 cm), ranging from 15 cm to 29 cm.[3] Medical problems of the urethra Micrograph of urethral cancer (urothelial cell carcinoma), a rare problem of the urethra. Hypospadias and epispadias are forms of abnormal development of the urethra
in the male, where the meatus is not located at the distal end of the penis (it occurs lower than normal with
hypospadias, and higher with
epispadias). In a severe chordee, the urethra can develop between the penis and the scrotum. Infection of the urethra is urethritis, said to be more common in females than
males. Urethritis is a common cause of dysuria (pain when urinating). Related to urethritis is so called urethral syndrome Passage of kidney stones through the urethra can be painful, which can lead to urethral strictures. Cancer of the urethra.
Main article: urethral cancer Foreign bodies in the urethra are
uncommon, but there have been medical
case reports of self-inflicted injuries, a
result of insertion of foreign bodies into the urethra such as an electrical wire.[4] Investigations There is a common misconception among
males that women urinate through the
vagina. Endoscopy of the bladder via the urethra is called cystoscopy. Urine cytology. Sexual physiology The male urethra is the conduit for semen
during sexual intercourse. It also serves as a passage for urine to flow. Urine typically
contains epithelial cells shed from the
urinary tract. Urine cytology evaluates this
urinary sediment for the presence of
cancerous cells from the lining of the
urinary tract, and it is a convenient noninvasive technique for follow-up
analysis of patients treated for urinary
tract cancers. For this process, urine must
be collected in a reliable fashion, and if
urine samples are inadequate, the urinary
tract can be assessed via instrumentation. In urine cytology, collected urine is
examined microscopically. One limitation,
however, is the inability to definitively
identify low-grade cancer cells and urine
cytology is used mostly to identify high-
grade tumors.

VAGINA

The vagina (from Latin vagĭna, literally "sheath" or "scabbard") is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the oviduct. The Latinate plural "vaginae" is rarely used in English. The word vagina is quite often used colloquially to refer to the vulva or female genitals generally; technically speaking, the vagina is a specific internal structure. In humans, the passage leads from the opening of the vulva to the uterus (womb). It lies midway between the anal tract and the urethra.[1] Location and structure The human vagina is an elastic muscular canal that extends from the cervix to the vulva .[2] Although there is wide anatomical variation, the length of the unaroused vagina of a woman of child-bearing age is approximately 6 to 7.5 cm (2.5 to 3 in) across the anterior wall (front), and 9 cm (3.5 in) long across the posterior wall (rear).[3] During sexual arousal the vagina expands in both length and width.[4] Its elasticity allows it to stretch during sexual intercourse and during birth to offspring.[5] The vagina connects the superficial vulva to the cervix of the deep uterus. If the woman stands upright, the vaginal tube points in an upward-backward direction and forms an angle of slightly more than 45 degrees with the uterus. The vaginal opening is at the caudal end of the vulva, behind the opening of the urethra. The upper one-fourth of the vagina is separated from the rectum by the recto- uterine pouch. Above the vagina is the Mons pubis. The vagina, along with the inside of the vulva, is reddish pink in color, as are most healthy internal mucous membranes in mammals. A series of ridges produced by folding of the wall of the outer third of the vagina is called the vaginal rugae. They are transverse epithelial ridges and their function is to provide the vagina with increased surface area for extension and stretching. Vaginal lubrication is provided by the Bartholin's glands near the vaginal opening and the cervix. The membrane of the vaginal wall also produces moisture, although it does not contain any glands. Before and during ovulation, the cervix's mucus glands secretes different variations of mucus, which provides an alkaline environment in the vaginal canal that is favorable to the survival of sperm. The hymen is a membrane of tissue which is situated at the opening of the vagina. As in many female animals, the hymen covers the opening of the vagina from birth until it is ruptured during sexual or other activity. The tissue may be ruptured by vaginal penetration, delivery, a pelvic examination, injury, or sports. The absence of a hymen does not indicate prior sexual activity, as it is not always ruptured during sexual intercourse.[6] Similarly, its presence does not indicate a lack of prior sexual activity, as light activity may not rupture it, and it can be surgically restored. Function The vagina has several biological functions. Sexual activity Further information: Human sexual activity The concentration of the nerve endings that lie close to the entrance of a woman's vagina can provide pleasurable sensation during sexual activity, when stimulated in a way that the particular woman enjoys. During sexual arousal, and particularly the stimulation of the clitoris, the walls of the vagina self-lubricate. This reduces friction that can be caused by various sexual activities. Research has found that portions of the clitoris extend into the vulva and vagina.[7] With arousal, the vagina lengthens rapidly to an average of about 4 in.(10 cm), but can continue to lengthen in response to pressure.[8] As the woman becomes fully aroused, the vagina tents (last ²⁄₃) expands in length and width, while the cervix retracts.[9] The walls of the vagina are composed of soft elastic folds of mucous membrane which stretch or contract (with support from pelvic muscles) to the size of the inserted penis or other object, stimulating the penis and helping to cause the male to experience orgasm and ejaculation, thus enabling fertilization. G-Spot Main article: G-Spot Structure of the wall of vagina An erogenous zone commonly referred to as the G-Spot (also known as the Gräfenberg Spot) is located at the anterior wall of the vagina, about five centimeters in from the entrance. Some women experience intense pleasure if the G-Spot is stimulated appropriately during sexual activity. A G-Spot orgasm may be responsible for female ejaculation, leading some doctors and researchers to believe that G-Spot pleasure comes from the Skene's glands, a female homologue of the prostate, rather than any particular spot on the vaginal wall. [10][11][12] Some researchers dispute the existence of the G- Spot.[13] Childbirth During childbirth, the vagina provides the channel to deliver the infant from the uterus to its independent life outside the body of the mother. During birth, the elasticity of the vagina allows it to stretch to many times its normal diameter. The vagina is often typically referred to as the birth canal in the context of pregnancy and childbirth, though the term is, by definition, the area between the outside of the vagina and the fully dilated uterus. [14] Uterine secretions The vagina provides a path for menstrual blood and tissue to leave the body. In industrial societies, tampons, menstrual cups and sanitary napkins may be used to absorb or capture these fluids. Clinical relevance An ultrasound showing the urinary bladder (1), uterus (2), and vagina (3) Main article: Vulvovaginal health The vagina is self-cleansing and therefore usually needs no special treatment. Doctors generally discourage the practice of douching.[15] Since a healthy vagina is colonized by a mutually symbiotic flora of microorganisms that protect its host from disease-causing microbes, any attempt to upset this balance may cause many undesirable outcomes, including but not limited to abnormal discharge and yeast infection. The acidity of a healthy vagina of a woman of child-bearing age (a pH of around 4.5) is due to the degradation of glycogen to the lactic acid by enzymes secreted by the Döderlein's bacillus. This is a normal commensal of the vagina. The acidity retards the growth of many strains of dangerous microbes.[16] The vagina is examined during gynecological exams, often using a speculum, which holds the vagina open for visual inspection of the cervix or taking of samples (see pap smear). Vaginismus Main article: Vaginismus Vaginismus, not to be confused with Vaginitis, refers to an involuntary tightening of the vagina, due to a conditioned reflex of the muscles in the area. It can affect any form of vaginal penetration, including sexual intercourse, insertion of tampons, and the penetration involved in gynecological examinations. Various psychological and physical treatments are possible to help alleviate it. Signs of disease Vaginal diseases present with lumps, discharge and sores. Lumps The presence of unusual lumps in the wall or base of the vagina is always abnormal. The most common of these is Bartholin's cyst.[17] The cyst, which can feel like a pea, is formed by a blockage in glands which normally supply the opening of the vagina. This condition is easily treated with minor surgery or silver nitrate. Other less common causes of small lumps or vesicles are herpes simplex. They are usually multiple and very painful with a clear fluid leaving a crust. They may be associated with generalized swelling and are very tender. Lumps associated with cancer of the vaginal wall are very rare and the average age of onset is seventy years.[18] The most common form is squamous cell carcinoma, then cancer of the glands or adenocarcinoma and finally, and even more rarely, melanoma. A speculum allows physicians to examine the vagina and cervix. Discharge The great majority of vaginal discharges are normal or physiological and include blood or menses (from the uterus), the most common, and clear fluid either as a result of sexual arousal or secretions from the cervix. Other non infective causes include dermatitis, discharge from foreign bodies such as retained tampons or foreign bodies inserted by curious female children into their own vaginas. Non-sexually transmitted discharges occur from bacterial vaginosis and thrush or candidiasis. The final group of discharges include the sexually transmitted diseases gonorrhea, chlamydia and trichomoniasis. The discharge from thrush is slightly pungent and white, that from trichomoniasis more foul and greenish, and that from foreign bodies resembling the discharge of gonorrhea, greyish or yellow and purulent (like pus).[19] Sores All sores involve a breakdown in the walls of the fine membrane of the vaginal wall. The most common of these are abrasions and small ulcers caused by trauma. While these can be inflicted during rape most are actually caused by excessive rubbing from clothing or improper insertion of a sanitary tampon. The typical ulcer or sore caused by syphilis is painless with raised edges. These are often undetected because they occur mostly inside the vagina. The sores of herpes which occur with vesicles are extremely tender and may cause such swelling that passing urine is difficult. In the developing world a group of parasitic diseases also cause vaginal ulceration such as Leishmaniasis but these are rarely encountered in the west. HIV/AIDS can be contracted through the vagina during intercourse but is not associated with any local vaginal or vulval disease. [20] All the above local vulvovaginal diseases are easily treated. Often only shame prevents patients from presenting for treatment.

OVARY

The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands. Human anatomy Ovaries are oval shaped. The ovary (for a given side) is located in the lateral wall of the pelvis in a region called the ovarian fossa. The fossa usually lies beneath the external iliac artery and in front of the ureter and the internal iliac artery. The ovaries aren't attached to the fallopian tubes but to the outer layer of the uterus via the ovarian ligaments. Usually each ovary takes turns releasing eggs every month; however, if there was a case where one ovary was absent or dysfunctional then the other ovary would continue providing eggs to be released. Hormones Ovaries secrete both estrogen and progesterone. Estrogen is responsible for the appearance of secondary sex characteristics of anatomically female people at puberty and for the maturation and maintenance of the reproductive organs in their mature functional state. Progesterone functions with estrogen by promoting menstrual cycle cyclic changes in the endometrium. Ligaments In the human the paired ovaries lie within the pelvic cavity, on either side of the uterus, to which they are attached via a fibrous cord called the ovarian ligament. The ovaries are uncovered in the peritoneal cavity but are tethered to the body wall via the suspensory ligament of the ovary. The part of the broad ligament of the uterus that covers the ovary is known as the mesovarium. Thus, the ovary is the only organ in the human body which is totally invaginated into the peritonium, making it the only interperitoneal organ (not to be confused with intraperitoneal). Extremities There are two extremities to the ovary: The end to which the uterine tube attaches is called the tubal extremity. The other extremity is called the uterine extremity. It points downward, and it is attached to the uterus via the ovarian ligament. Histology Cell types Follicular cells flat epithelial cells that originate from surface epithelium covering the ovary granulosa cells - surrounding follicular cells have changed from flat to cuboidal and proliferated to produce a stratified epithelium Gametes[1] Section of the ovary of a newly born child. Germinal epithelium is seen at top. Primitive ova are seen in their cell-nests. The Genital cord or genital ridge is still discernible in this young child. A blood vessel and an ovarian follicle is also seen The outermost layer is called the ovarian surface epithelium (previously known as the germinal epithelium). The tunica albuginea covers the cortex. The ovarian cortex consists of ovarian follicles and stroma in between them. Included in the follicles are the cumulus oophorus, membrana granulosa (and the granulosa cells inside it), corona radiata, zona pellucida, and primary oocyte . The zona pellucida, theca of follicle, antrum and liquor folliculi are also contained in the follicle. Also in the cortex is the corpus luteum derived from the follicles. The innermost layer is the ovarian medulla. It can be hard to distinguish between the cortex and medulla, but follicles are usually not found in the medulla. In other animals Ovaries of some kind are found in the female reproductive system of many animals that employ sexual reproduction, including invertebrates. However, they develop in a very different way in most invertebrates than they do in vertebrates, and are not truly homologous.[2] Many of the features found in human ovaries are common to all vertebrates, including the presence of follicular cells, tunica albuginea, and so on. However, many species produce a far greater number of eggs during their lifetime than do humans, so that, in fish and amphibians, there may be hundreds, or even millions of fertile eggs present in the ovary at any given time. In these species, fresh eggs may be developing from the germinal epithelium throughout life. Corpora lutea are found only in mammals, and in some elasmobranch fish; in other species, the remnants of the follicle are quickly resorbed by the ovary. In birds, reptiles, and monotremes, the egg is relatively large, filling the follicle, and distorting the shape of the ovary at maturity. [2] Amphibians and reptiles have no ovarian medulla; the central part of the ovary is a hollow, lymph-filled space. The ovary of teleosts is also often hollow, but in this case, the eggs are shed into the cavity, which opens into the oviduct.[2] Although most normal female vertebrates have two ovaries, this is not the case in all species. In birds and platypuses, the right ovary never matures, so that only the left is functional. In some elasmobranchs, the reverse is true, with only the right ovary fully developing. In the primitive jawless fish, and some teleosts, there is only one ovary, formed by the fusion of the paired organs in the embryo.[2] Cryopreservation Cryopreservation of ovarian tissue, often called Ovarian Tissue Cryopreservation , is of interest to women who want to preserve their reproductive function beyond the natural limit, or whose reproductive potential is threatened by cancer therapy,[3] for example in hematologic malignancies or breast cancer. [4] The procedure is to take a part of the ovary and carry out slow freezing before storing it in liquid nitrogen whilst therapy is undertaken. Tissue can then be thawed and implanted near the fallopian, either orthotopic (on the natural location) or heterotopic (on the abdominal wall),[4], where it starts to produce new eggs, allowing normal conception to take place. [5] A study of 60 procedures concluded that ovarian tissue harvesting appears to be safe.[4] The ovarian tissue may also be transplanted into mice that are immunocompromised (SCID mice) to avoid graft rejection, and tissue can be harvested later when mature follicles have developed.

SIGMOID COLON

The sigmoid colon (pelvic colon) is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about 40 cm. in length, and normally lies within the pelvis, but on account of its freedom of movement it is liable to be displaced into the abdominal cavity. Path It begins at the superior aperture of the lesser pelvis, where it is continuous with the iliac colon, and passes transversely across the front of the sacrum to the right side of the pelvis. (The name sigmoid aptly means S-shaped.) It then curves on itself and turns toward the left to reach the middle line at the level of the third piece of the sacrum, where it bends downward and ends in the rectum. Coverings It is completely surrounded by peritoneum (and thus is not retroperitoneal), which forms a mesentery (sigmoid mesocolon), which diminishes in length from the center toward the ends of the loop, where it disappears, so that the loop is fixed at its junctions with the iliac colon and rectum, but enjoys a considerable range of movement in its central portion. Innervation Pelvic splanchnic nerves are the primary source for parasympathetic innervation. Lumbar splanchnic nerves provide sympathetic innervation via the inferior mesenteric ganglion. Relations Behind the sigmoid colon are the external iliac vessels, the left Piriformis, and left sacral plexus of nerves. In front, it is separated from the bladder in the male, and the uterus in the female, by some coils of the small intestine.

UTERUS

The uterus (from Latin "uterus", plural uteri or "uteruses") or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species. It is within the uterus that the fetus develops during gestation, usually developing completely in placental mammals such as humans and partially in marsupials such as kangaroos and opossums. Two uteruses usually form initially in a female fetus, and in placental mammals they may partially or completely fuse into a single uterus depending on the species. In many species with two uteruses, only one is functional. Humans and other higher primates such as chimpanzees, along with horses, usually have a single completely fused uterus, although in some individuals the uteruses may not have completely fused. The term uterus is used consistently within the medical and related professions, while the Germanic derived term womb is also common in everyday usage in the English language. Most animals that lay eggs, such as birds and reptiles, have an oviduct instead of a uterus. In monotremes, mammals which lay eggs and include the platypus, either the term uterus or oviduct is used to describe the same organ, but the egg does not develop a placenta within the mother and thus does not receive further nourishment after formation and fertilization. Marsupials have two uteruses, each of which connect to a lateral vagina and which both use a third, middle "vagina" which functions as the birth canal. Marsupial embryos form a choriovitelline "placenta" (which can be thought of as something between a monotreme egg and a "true" placenta), in which the egg's yolk sac supplies a large part of the embryo's nutrition but also attaches to the uterine wall and takes nutrients from the mother's bloodstream. Function The uterus consists of a body and a cervix.The cervix protrudes into the vagina. The uterus is held in position within the pelvis by condensations of endopelvic fascia, which are called ligaments. These ligaments include the pubocervical, transverse. cervical ligaments cardinal ligaments, and the uterosacral ligaments. It is covered by a sheet-like fold of peritoneum, the broad ligament.[1] The uterus is essential in sexual response by directing blood flow to the pelvis and to the external genitalia, including the ovaries, vagina, labia, and clitoris. The reproductive function of the uterus is to accept a fertilized ovum which passes through the utero-tubal junction from the fallopian tube. It implants into the endometrium, and derives nourishment from blood vessels which develop exclusively for this purpose. The fertilized ovum becomes an embryo, attaches to a wall of the uterus, creates a placenta, and develops into a fetus (gestates) until childbirth. Due to anatomical barriers such as the pelvis, the uterus is pushed partially into the abdomen due to its expansion during pregnancy. Even during pregnancy the mass of a human uterus amounts to only about a kilogram (2.2 pounds). Forms in mammals In mammals, the four main forms in which it is found are: Duplex There are two wholly separate uteri, with one fallopian tube each. Found in marsupials (such as kangaroos, Tasmanian devils, opossums, etc.), rodents (such as mice, rats, and guinea pigs), and lagomorpha (rabbits and hares). Bipartite The two uteri are separate for most of their length, but share a single cervix. Found in ruminants (deer, moose, elk etc.), and cats. Bicornuate The upper parts of the uterus remain separate, but the lower parts are fused into a single structure. Found in dogs, pigs, elephants, whales, dolphins, and prosimian primates among others. Simplex The entire uterus is fused into a single organ. Found in higher primates (including humans and chimpanzees) . Occasionally, some individual females (including humans) may have a bicornuate uterus, a uterine malformation where the two parts of the uterus fail to fuse completely during fetal development. In monotremes such as the platypus, the uterus is duplex and rather than nurturing the embryo, secretes the shell around the egg. It is essentially identical with the shell gland of birds and reptiles, with which the uterus is homologous.[2] Anatomy The uterus is located inside the pelvis immediately dorsal (and usually somewhat rostral) to the urinary bladder and ventral to the rectum. The human uterus is pear- shaped and about 3 in. (7.6 cm) long. A female's uterus can be divided anatomically into four segments: The fundus, corpus, cervix and the internal os. Regions From outside to inside, the path to the uterus is as follows: Cervix uteri - "neck of uterus" External orifice of the uterus Canal of the cervix Internal orifice of the uterus corpus uteri - "Body of uterus" Cavity of the body of the uterus Fundus (uterus) Layers The layers, from innermost to outermost, are as follows: Endometrium The lining of the uterine cavity is called the "endometrium". It consists of the functional endometrium and the basal endometrium from which the former arises. Damage to the basal endometrium results in adhesion formation and/or fibrosis (Asherman's syndrome). In all placental mammals, including humans, the endometrium builds a lining periodically which is shed or reabsorbed if no pregnancy occurs. Shedding of the functional endometrial lining is responsible for menstrual bleeding (known colloquially as a "period" in humans with a cycle of about 28 days) throughout the fertile years of a female and for some time beyond. Depending on the species, menstrual cycles may vary from a few days to six months, but can vary widely even in the same individual, often stopping for several cycles before resuming. Marsupials and monotremes do not have menstruation. Myometrium The uterus mostly consists of smooth muscle, known as "myometrium." The innermost layer of myometrium is known as the junctional zone, which becomes thickened in adenomyosis. Parametrium The loose connective tissue around the uterus. Perimetrium The peritoneum covering of the fundus and ventral and dorsal aspects of the uterus. Support The uterus is primarily supported by the pelvic diaphragm, perineal body and the urogenital diaphragm. Secondarily, it is supported by ligaments and the peritoneum (broad ligament of uterus)[3] Axes Normally the uterus lies in anteversion & anteflexion.Antiversion is a forward angle between the axis of the cervix and that of the vagina measuring about 90 degree,provided the urinary bladder and the rectum are empty.Antiflexion is a forward angle between the body and cervix at the isthmus measuring about 125 degree,provided the bladder and rectum are empty. Major ligaments It is held in place by several peritoneal ligaments, of which the following are the most important (there are two of each): Name From To Uterosacral ligament Posterior cervix Anterior face of sacrum Cardinal ligaments Side of the cervix Ischial spines Pubocervical ligament[3] Side of the cervix Pubic symphysis Position The uterus is in the middle of the pelvic cavity in frontal plane (due to ligamentum latum uteri). The fundus does not surpass the linea terminalis, while the vaginal part of the cervix does not extend below interspinal line. The uterus is mobile and moves under the pressure of the full bladder or full rectum anteriorly, whereas if both are full it moves upwards. Increased intraabdominal pressure pushes it downwards. The mobility is conferred to it by musculo-fibrous apparatus that consists of suspensory and sustentacular part. Under normal circumstances the suspensory part keeps the uterus in anteflexion and anteversion (in 90% of women) and keeps it "floating" in the pelvis. The meaning of these terms are described below: Distinction More common Less common Position tipped "Anteverted": Tipped forward "Retroverted": Tipped backwards Position of fundus "Anteflexed": Fundus is pointing forward relative to the cervix "Retroflexed": Fundus is pointing backwards Sustentacular part supports the pelvic organs and comprises the larger pelvic diaphragm in the back and the smaller urogenital diaphragm in the front. The pathological changes of the position of the uterus are: retroversion/retroflexion, if it is fixed hyperanteflexion - tipped too forward; most commonly congenital, but may be caused by tumors anteposition, retroposition, lateroposition - the whole uterus is moved; caused by parametritis or tumors elevation, descensus, prolapse rotation (the whole uterus rotates around its longitudinal axis), torsion (only the body of the uterus rotates around) inversion In cases where the uterus is "tipped", also known as retroverted uterus, women may have symptoms of pain during sexual intercourse, pelvic pain during menstruation, minor incontinence, urinary track infections, problems trying to conceive, and difficulty using tampons. A pelvic examination by a doctor can determine if a uterus is tipped.[4] Blood supply Vessels of the uterus and its appendages, rear view. Schematic diagram of uterine arterial vasculature seen as a cross-section through the myometrium and endometrium. The uterus is supplied by arterial blood both from the uterine artery and the ovarian artery. Development The bilateral Müllerian ducts form during early fetal life. In males, MIF secreted from the testes leads to their regression. In females these ducts give rise to the Fallopian tubes and the uterus. In humans the lower segments of the two ducts fuse to form a single uterus, however, in cases of uterine malformations this development may be disturbed. The different uterine forms in various mammals are due to various degrees of fusion of the two Müllerian ducts. Pathology Some pathological states include: Prolapse of the uterus Carcinoma of the cervix – malignant neoplasm Carcinoma of the uterus – malignant neoplasm Fibroids – benign neoplasms Adenomyosis – ectopic growth of endometrial tissue within the myometrium Pyometra – infection of the uterus, most commonly seen in dogs Uterine malformations mainly congenital malformations including Uterine Didelphys, bicornuate uterus and septate uterus. It also includes congenital absence of the uterus Rokitansky syndrome Asherman's syndrome , also known as intrauterine adhesions occurs when the basal layer of the endometrium is damaged by instrumention (e.g. D&C) or infection (e.g. endometrial tuberculosis) resulting in endometrial scarring followed by adhesion formation which partially or completely obliterates the uterine cavity.

FORNIX

The fornices of the vagina (sing. fornix of the vagina or fornix vaginae) are the deepest portions of the vagina, extending into the recesses created by the vaginal portion of cervix. The word 'fornix' is Latin for 'arch'. There are three named fornices: The posterior fornix is the larger recess, behind the cervix. It is close to the rectouterine pouch. There are two smaller recesses in front and at the sides: the anterior fornix is close to the vesicouterine pouch. the lateral fornix. During sexual intercourse in the missionary position, the tip of the penis reaches the anterior fornix, while in the rear-entry position it reaches the posterior fornix.[1] Some women receive enjoyment from stimulation of the fornices, while other women say that their fornices cannot be stimulated without stimulation of the cervix, which may be painful.[citation needed] The fornices appear to be close to at least two erogenous zones, the AFE zone, which is near the anterior fornix, and the cul-de- sac, which is near the posterior fornix.

CERVIX

The cervix (or neck of the uterus) is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is cylindrical or conical in shape and protrudes through the upper anterior vaginal wall. Approximately half its length is visible with appropriate medical equipment; the remainder lies above the vagina beyond view. It is occasionally called "cervix uteri". Cervix means neck in Latin. AnatomyThe cervix with cervical mucous The cervical os Ectocervix The portion projecting into the vagina is referred to as the portio vaginalis or ectocervix. On average, the ectocervix is 3 cm long and 2.5 cm wide. It has a convex, elliptical surface and is divided into anterior and posterior lips. External os Main article: External orifice of the uterus The ectocervix's opening is called the external os. The size and shape of the external os and the ectocervix varies widely with age, hormonal state, and whether the woman has had a vaginal birth. In women who have not had a vaginal birth the external os appears as a small, circular opening. In women who have had a vaginal birth, the ectocervix appears bulkier and the external os appears wider, more slit-like and gaping. Endocervical canal The passageway between the external os and the uterine cavity is referred to as the endocervical canal. It varies greatly in length and width, along with the cervix overall. Flattened anterior to posterior, the endocervical canal measures 7 to 8 mm at its widest in reproductive-aged women. Internal os The endocervical canal terminates at the internal os which is the opening of the cervix inside the uterine cavity. Histology The epithelium of the cervix is varied. The ectocervix (more distal, by the vagina) is composed of nonkeratinized stratified squamous epithelium. The endocervix (more proximal, within the uterus) is composed of simple columnar epithelium. [1] The area adjacent to the border of the endocervix and ectocervix is known as the transformation zone. The Transformation zone undergoes metaplasia numerous times during normal life. When the endocervix is exposed to the harsh acidic environment of the vagina it undergoes metaplasia to squamous epithelium which is better suited to the vaginal environment. Similarly when the ectocervix enters the less harsh uterine area it undergoes metaplasia to become columnar epithelium. Times in life when this metaplasia of the transformation zone occurs: puberty; when the endocervix everts (moves out) of the uterus with the changes of the cervix associated with the normal menstrual cycle post-menopause; the uterus shrinks moving the transformation zone upwards All these changes are normal and the occurrence is said to be physiological. However, all this metaplasia does increase the risk of cancer in this area - the transformation zone is the most common area for cervical cancer to occur. At certain times of life, the columnar epithelium is replaced by metaplastic squamous epithelium, and is then known as the transformation zone. Nabothian cysts are often found in the cervix.[2] Cervical mucus Mucus plug Cervical Mucus is 90% water. Depending on the water content which varies during the menstrual cycle the mucus functions as a barrier or a transport medium to spermatoza. Cervical mucus also contains electrolytes (calcium, sodium and potassium), organic components such as glucose, amino acids and soluble proteins. [3] Cervical mucus contains trace elements including zinc, copper, iron, mangenese and selenium, the levels of which vary dependant on cyclical hormone variation during different phases of the menstrual cycle [4] Various enzymes have been identified in human cervical mucus. Glycerol is a natural ingredient of human cervical fluid.[5][6][7][8] Studies have shown that the amount of glycerol in cervical fluid increases during sexual excitement.[6] This increase in glycerol has been postulated to be responsible for the lubricating quality of this fertile cervical fluid and may be biologically relevant during the early phase of reproductive events. After a menstrual period ends, the external os is blocked by mucus that is thick and acidic. This "infertile" mucus blocks spermatozoa from entering the uterus.[9] For several days around the time of ovulation, "fertile" types of mucus are produced; they have a higher water content, are less acidic, and have a ferning pattern that helps guide spermatozoa through the cervix.[10] This ferning is a branching pattern seen in the mucus when observed with low magnification. Some methods of fertility awareness involve estimating a woman's periods of fertility and infertility by observing changes in her body. Among these changes are several involving the quality of her cervical mucus: the sensation it causes at the vulva, its elasticity ( Spinnbarkeit), its transparency, and the presence of ferning. [10] Cervical mucus Most methods of hormonal contraception work primarily by preventing ovulation, but their effectiveness is increased because they prevent the fertile types of cervical mucus from being produced. Conversely, methods of thinning the mucus may help to achieve pregnancy. One suggested method is to take guaifenesin in the few days before ovulation. [11] During pregnancy the cervix is blocked by a special antibacterial mucosal plug which prevents infection, somewhat similar to its state during the infertile portion of the menstrual cycle. The mucus plug comes out as the cervix dilates in labor or shortly before. Cervical position After menstruation and directly under the influence of estrogen, the cervix undergoes a series of changes in position and texture. During most of the menstrual cycle, the cervix remains firm, like the tip of the nose, and is positioned low and closed. However, as a woman approaches ovulation, the cervix becomes softer, and rises and opens in response to the high levels of estrogen present at ovulation. [12] These changes, accompanied by the production of fertile types of cervical mucus, support the survival and movement of sperm. Function During menstruation the cervix stretches open slightly to allow the endometrium to be shed. This stretching is believed to be part of the cramping pain that many women experience. Evidence for this is given by the fact that some women's cramps subside or disappear after their first vaginal birth because the cervical opening has widened. During childbirth, contractions of the uterus will dilate the cervix up to 10 cm in diameter to allow the child to pass through. During orgasm, the cervix convulses and the external os dilates. Robin Baker and Mark A. Bellis, both at the University of Manchester, first proposed that this behavior would tend to draw semen in the vagina into the uterus, increasing the likelihood of conception.[13] This explanation has been called the "upsuck theory of female orgasm." Komisaruk, Whipple, and Beyer-Flores, in their book, The Science of Orgasm, claimed there is evidence in support of the upsuck theory. [14] Science historian Elisabeth Lloyd, author of The Case of the Female Orgasm, questioned the logic of this theory and the quality of the experimental data used to back it,[15] commenting in 2005: "[The upsuck theory] has been widely accepted in the community of scientists for the past 12 years... But unfortunately the evidence for it is really badly flawed. In one of their tables 73% of the data came from one woman. It's really quite shocking that for 12 years this research has been taught as "fact" all across the US, Canada and the UK."[16] Short cervix[17] is the strongest predictor of preterm birth.[18][19][20] Some treatments to prevent cervical cancer, such as LEEP, cold-knife conization, or cryotherapy may shorten the cervix. Cervical cancer Main article: Cervical cancer Human papillomavirus (HPV) infection is a necessary factor in the development of nearly all cases of cervical cancer. HPV vaccines can reduce the chance of developing cervical cancer, if administered before initiation of sexual activity. Potentially pre-cancerous changes in the cervix can be detected by a Pap smear, in which epithelial cells are scraped from the surface of the cervix and examined under a microscope. With appropriate treatment of detected abnormalities, cervical cancer can be prevented. Most women who develop cervical cancer have never had a Pap smear, or have not had one within the last five years. Worldwide, cervical cancer is the fifth most deadly cancer in women. [21] It affects about 16 per 100,000 women per year and kills about 9 per 100,000 per year.[22] Pap smear screening has greatly reduced cervical cancer incidence and mortality in nations with regular screening programs. Lymphatic drainage The lymphatic drainage of the cervix is along the uterine arteries and cardinal ligaments to the parametrial, external iliac vein, internal iliac vein, and obturator and presacral lymph nodes. From these pelvic lymph nodes, drainage then proceeds to the paraaortic lymph nodes. In some women, the lymphatics drain directly to the paraaortic nodes.

RECTUM

The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long.[citation needed] Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. Role in human defecation The rectum intestinum acts as a temporary storage site for feces. As the rectal walls expand due to the materials filling it from within, stretch receptors from the nervous system located in the rectal walls stimulate the desire to defecate. If the urge is not acted upon, the material in the rectum is often returned to the colon where more water is absorbed. If defecation is delayed for a prolonged period, constipation and hardened feces results.[citation needed] When the rectum becomes full, the increase in intrarectal pressure forces the walls of the anal canal apart, allowing the fecal matter to enter the canal. The rectum shortens as material is forced into the anal canal and peristaltic waves propel the feces out of the rectum. The internal and external sphincter allow the feces to be passed by muscles pulling the anus up over the exiting feces. Supports of rectum Pelvic floor formed by levator ani muscles. Fascia of Waldeyer Lateral ligaments of rectum which are formed by the condensation of pelvic fascia Rectovesical fascia of Denonvillers, which extends from rectum behind to the seminal vesicles and prostate in front. Pelvic peritoneum Perineal body Medical procedures For the diagnosis of certain ailments, a rectal exam may be done. Suppositories may be inserted into the rectum as a route of administration for medicine. The endoscopic procedures colonoscopy and sigmoidoscopy are performed to diagnose diseases such as cancer. Digital Rectal Stimulation, the insertion of one finger into the rectum, is used to induce peristalsis in patients whose own peristaltic reflex is inadequate to fully empty the rectum. Manual Evacuation is the use of a gloved finger to evacuate faeces from the rectum, and is utilised primarily in acute constipation and also the long-term management of neurogenic bowel, seen most frequently in people with a spinal cord injury or multiple sclerosis. Temperature taking Main article: Normal human body temperature related article: rectal thermometry Body temperature can also be taken in the rectum. Rectal temperature can be taken by inserting a medical thermometer not more than 25 mm (1 inch) into the rectum via the anus. A mercury thermometer should be inserted for 3 to 5 minutes; a digital thermometer should remain inserted until it beeps. Due to recent concerns related to mercury poisoning, the use of mercury thermometers is outlawed. Normal rectal temperature generally ranges from 36 to 38 °C (97.6 to 100.4 °F) and is about 0.5 °C (1 °F) above oral (mouth) temperature and about 1 °C (2 °F) above axilla (armpit) temperature.[citation needed] Pediatricians recommend that parents take infants' and toddlers' temperature in the rectum for two reasons: 1. Rectal temperature is the closest to core body temperature and in young children, accuracy is critical. 2. Younger children are unable to cooperate when having their temperature taken by mouth (oral), which is recommended for children ages 6 and above as well as adults. In recent years, the introduction of tympanic (ear) thermometers and changing attitudes on privacy and modesty have led some parents and doctors to discontinue taking rectal temperatures.[citation needed] Sexual stimulation Due to the proximity of the anterior wall of the rectum to the vagina in females or to the prostate in males and the shared nerves thereof, rectal stimulation or penetration can result in sexual arousal. For further information on this aspect, see anal sex.

ANUS

The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest, such as bones;[1] food material after all the nutrients have been extracted, for example cellulose or lignin; ingested matter which would be toxic if it remained in the digestive tract; and dead or excess gut bacteria and other endosymbionts. Amphibians, reptiles, and birds use the same orifice for excreting liquid and solid wastes, and for copulation and egg-laying; this orifice is known as the cloaca. Monotreme mammals also have a cloaca, which is thought to be a feature inherited from the earliest amniotes via the therapsids. Marsupials have two nether orifices: one for excreting both solids and liquids; the other for reproduction, which appears as a vagina in females and a penis in males. Female placental mammals have completely separate orifices for defecation, urination, and reproduction; males have one opening for defecation and another for both urination and reproduction, although the channels flowing to that orifice are almost completely separate. The development of the anus was an important stage in the evolution of multicellular animals. In fact it appears to have happened at least twice, following different paths in protostomes and deuterostomes. This accompanied or facilitated other important evolutionary developments: the bilaterian body plan; the coelom, an internal cavity that provided space for a circulatory system and, in some animals, formed a hydrostatic skeleton which enables worm-like animals to burrow; metamerism, in which the body was built of repeated "modules" which could later specialize, for example the heads of most arthropods are composed of fused, specialized segments. Etymology First attested in 1658, from Latin anus (“ring, anus”), from Proto-Indo-European *ano- (“ring”). See also anal, annular, annelid. Development Main articles: protostome and deuterostome In animals at least as complex as an earthworm, the embryo forms a dent on one side, the blastopore, which deepens to become the archenteron, the first phase in the growth of the gut. In deuterostomes, the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The protostomes were so named because it used to be thought that in their embryos the dent formed the mouth while the anus was formed later, at the opening made by the other end of the gut. More recent research, however, shows that in protostomes the edges of the dent close up in the middle, leaving openings at the ends which become the mouth and anus.

THE INGUINAL REGION

The Inguinal Region The inguinal region is very important
surgically because it is the site of inguinal hernias. Although both sexes may get these, it is
much more common in males. The inguinal region is an area of
weakness in the anterior abdominal wall because of the prenatal penetration of
the wall by the testis and the spermatic cord. The Inguinal Canal This is an oblique passage, about 4 cm long in adults, through the inferior part of the anterior abdominal wall. It runs inferomedially, just superior and parallel to the medial half of the inguinal ligament. The inguinal canal has two walls (anterior and posterior), two openings (the superficial and deep inguinal rings), a roof (superior wall), and a floor (inferior wall). Owing to the obliquity of the inguinal
canal, the deep and superficial inguinal rings do not coincide. Increases in intra-abdominal pressure act
on the deep inguinal ring, which forces the posterior wall of the canal against
the anterior wall. Contraction of the external oblique muscle approximates the anterior wall of the canal with the posterior wall. Contraction of the internal oblique and transversus abdominis muscles causes the roof of the canal to descend and the passage is constricted. During standing, these muscles
continuous contract. During coughing and straining, the raise
intra-abdominal pressure threatens to
force some of the abdominal contents
through the canal, producing a hernia. However, vigorous contraction of the arched fleshy fibres of the internal oblique and transversus abdominis muscles "clamp down". The action is like a half-sphincter that helps prevent herniation. The conjoint tendon and rectus abdominis muscle also reinforce the superficial inguinal ring (as the external
oblique aponeurosis pushes against these
when intra-abdominal pressure rises). Back to top The Anterior Wall of the Inguinal Canal Formed mainly by the aponeurosis of the external oblique muscle. It is reinforced laterally by the fibres of
the internal oblique muscle; sometimes by the transversus abdominis muscle. The Posterior Wall of the Inguinal Canal Formed throughout by the transversalis fascia, which is reinforced medially by the conjoint tendon. The Floor of the Inguinal Canal This is formed by the superior surface of
the inguinal ligament and the lacunar ligament. The Roof of the Inguinal Canal It is formed by the arching fibres of the internal oblique and transversus abdominis muscles. The inferior epigastric artery lies at the medial boundary of the deep inguinal ring. Its pulsations form a useful landmark
during surgery for determining the
location of this ring. The Superficial Ring of the Inguinal
Canal This ring is more or less a triangular aperture (deficiency) in the aponeurosis of the external oblique muscle. The base of this triangle is formed by the public crest and the apex is directly superolateral. The sides of the triangle is formed by the medial and lateral crura (L. legs) of the superficial inguinal ring. Emerging from the superficial inguinal
ring is the spermatic cord in the male and the round ligament of the uterus in the female. In addition, the ilioinguinal nerve makes its exit through the ring to supply skin on
the superomedial aspect of the thigh. The central point of the superficial
inguinal ring is superior to the pubic tubercle. The superficial inguinal ring is just palpable superior and lateral to the
pubic tubercle. The Lateral Crus of the Superficial
Inguinal Ring This is formed by the part of the external oblique aponeurosis that is attached to the pubic tubercle via the inguinal
ligament. The spermatic cord rests on the inferior part of this crus. The Medial Crus of the Superficial Inguinal
Ring This is formed by the part of the external oblique aponeurosis that diverges to attach to the pubic bone and pubic crest,
medial to the pubic tubercle. Intercrural fibres from the inguinal ligament arch superomedially across the
superficial inguinal ring. These prevent the crura from spreading
apart. The Deep Ring of the Inguinal Canal This slit-like opening in the transversalis fascia is located just lateral to the inferior epigastric artery. The deep ring is immediately superior to
the midpoint of the inguinal ligament. The margins of the deep ring are not
sharply defined, as are those in the
superficial ring. Back to top The Spermatic Cord This cord suspends the testis in the
scrotum and consists of the structures
running to and from the testis. They are surrounded by protective
coverings derived from the anterior abdominal wall. The spermatic cord begins at the deep inguinal ring, lateral to the inferior epigastric artery, where its constituents assemble, and ends at the posterior
border of the testis. It passes through the inguinal canal, emerges at the superficial inguinal ring, and descends within the scrotum to the
testis. As the cord leaves the inguinal canal, it acquires its 3rd covering, the external spermatic fascia. Constituents of the Spermatic Cord 1. The Ductus Deferens This is the large duct of the testis,
formerly called the vas deferens. It lies in the posterior part of the
spermatic cord and is easily palpable
because of its thick wall of smooth
muscle. 2. Arteries The testicular artery arises from the anterior aspect of the aorta at the level
of L2 vertebrae. This is the main artery supplying the
testis and the epididymis. The artery of the ductus deferens is a slender vessel that arises from the
inferior vesical artery. It accompanies the ductus deferens throughout its course and anastomoses
with the testicular artery near the testis. The cremasteric artery is a small vessel that arises from the inferior epigastric
artery. It supplies the cremaster muscle and other coverings of the spermatic cord. 3. Veins Up to 12 veins leaving the posterior surface of the testis anastomose to form
a pampiniform plexus (L. pampinus, tendril). This large vine-like plexus forms a large part of the spermatic cord, surrounding
the ductus deferens and arteries in the spermatic cord. 4. Nerves There are sympathetic fibres on the
arteries and both sympathetic and
parasympathetic fibres on the ductus deferens. The genital branch of the genitofemoral nerve passes into the spermatic cord and supplies the cremaster muscle. 5. Lymph Vessels Lymph vessels draining the testis and
immediately associated structures pass
superiorly in the spermatic cord. These vessels end in the lumbar and preaortic lymph nodes. Back to top Coverings of the Spermatic Cord The spermatic cord is covered by three
layers of fascia, derived from the anterior abdominal wall. The Internal Spermatic Fascia As the processus vaginalis
(embryological) evaginated the
transversalis fascia at the deep inguinal ring, it carried a thin layer of fascia that became the internal spermatic fascia. It constitutes the filmy innermost covering of the spermatic cord. The Cremaster Muscle and Cremasteric
Fascia As the processus vaginalis, with its
covering of transversalis fascia
evaginated under the edge of the internal oblique muscle, it acquired some of this muscle's fibres and its investing
fascia. These fibres form the cremaster muscle
and cremasteric fascia. The cremasteric fascia forms the middle
covering of the spermatic cord, which
contains loops of the cremaster muscle. The cremaster muscle, which is
continuous with the internal oblique muscle, reflexly draws the testis to a more superior position in the scrotum (cremasteric reflex), particularly in cold
temperatures. The External Spermatic Fascia As the external oblique muscle was evaginated by the processus vaginalis, it
formed the superficial inguinal ring and
an extension of its aponeurosis was
carried outward. This layer became the external spermatic
fascia, the thin outermost covering of the spermatic cord.

FERTILIZATION

Fertilisation Fertilisation can be defined as the fusion
of the sperm nucleus with the egg
nucleus to form a diploid cell known as
zygote. The fertilisation is internal in the human
reproductive system. It is achieved by
the insertion of the male organ, penis
into the vagina of the female. The sperms
are deposited in the vagina of the
females during a process called as copulation or sexual intercourse. The
release of sperms is called ejaculation
and at one ejaculation there may be upto
600 million sperms. Of these only a few thousands make the
journey from the vaginal canal to the
oviducts. This may take 4-8 hours. The
life of the sperm is 1-3 days after the
ejaculation. Each sperm is a small cell of about 50um
length and 2.5um diameter. Structure of a Sperm It consists of a head, middle piece and
the tail regions. The head consists of the
nucleus and a structure called the
acrosome at the tip. The acrosome
secretes lytic substances that break down
the walls of the egg for fertilisation. The beating of the tail propels the sperm
forward at the rate of 1-4 mm per
minute. Each egg or ovum is a spherical cell much
bigger than the sperm. It mainly consists
of a single nucleus and some reserve food
made of lipid droplets. Fertilisation of Human Egg In the fallopian tubes, many sperms
surround an egg. However, only one
enters the egg leaving behind the tail.
The enzymes of the acrosome digest the
several layers of tissue to reach the egg
cytoplasm. Once the sperm is inside, the male and female nuclei become lighter
and are called pro-nuclei. The two pro-
nuclei fuse forming a zygote. Once a sperm enters an egg, the
thickening of the outer walls of the egg
blocks the entry of other sperms. Once the egg is fertilised, ovulation and
menstruation do not take place. The
fertilised structure, now called the zygote
is diploid. It starts dividing and forms a
blastocyst, the first stage of an embryo.
The blastocyst gets implanted on the uterine walls. It then grows into a foetus. A Section through the Fallopian Tube and
Uterus Showing the Sequence from Fertilisation
to Implantation The foetus remains attached to the
mother through an umbilical cord which
is embedded in a tissue called placenta at one end. Foetus in Different Positions and Stages The placenta in turn is embedded into the
uterine wall and is richly supplied with
blood vessels. The nutrients from the
mother's blood pass into the umbilical
cord and the waste from the foetus pass
into the mother's blood through the placenta. The foetus is fully grown and ready to
emerge from the womb in 40 weeks. The
uterine walls start muscular contractions
called the labour that helps in pushing the
foetus to the outside through the vaginal
canal. The placenta detaches from the uterine wall once the baby is out. The
umbilical cord has to be cut and tied near
the baby's body.

INTERNAL VAGINAL ORGANS

The internal genital organs of the female
body are the vagina, the uterus, the two
fallopian tubes and the two ovaries. Vagina : The vagina is an elastic fibromuscular, hollow structure extending
upwards and backwards from the vulva . It connects the uterus to the external
surface of the body through the vaginal opening in the vulva . The vagina is the organ for sexual
intercourse in the female body and forms
the birth canal in labour during the delivery of a baby. It is also the opening
through which the menstrual blood flows
out during the menstrual period. It is about 2.5 cm wide and 7 cm to 9cm
long. But it has a great capacity to
distend as is seen during childbirth. The G-spot or the Graafenberg spot (also
spelt as 'Grafenberg') is believed to be an
erotic spot in the vagina that is highly
sensitive to sexual stimulus. It is said to
be a triangular area in the anterior
vaginal wall, about 2.5cm from the vaginal opening and along the urethra.
But anatomical dissection by many
researchers have not found evidence of
the existence of the G-spot. Uterus : The uterus is a hollow, muscular pear-shaped structure situated deep in
the pelvis and well protected by the
pelvic bones. It looks roughly like an inverted triangle
with the broad base as its roof and the
narrow apex at its lower end. This lower
end also called the cervix opens into the
vagina. The two angles on the two ends
of the base of the triangle is connected to the two Fallopian tubes. The adult uterus is about 8cm long and
5cm wide at its thickest part. Before the
onset of menstruation, its length ranges from 2cm to 5 cms.The weight varies
from 50gms to 80 gms. The non-pregnant
uterus can hold only about 5ml of fluid.
The inner lining of the uterus –called the ‘endometrium’- is a spongy area with a rich blood supply. Monthly shedding of
this endometrium results in the
phenomenon called ‘menstruation’. The muscles of the uterus have a great
capacity to increase both in number and
in size (up to 500 times its normal size)
during pregnancy.The uterus is the organ that receives, implants, retains and
nourishes the foetus till it is mature. It
increases gradually in size from the first trimester through the second trimester and upto the end of the third trimester. It then contracts and expels the foetus at
the time of labour and childbirth. Fallopian tubes : Also called the ‘Oviducts’, there are two fallopian tubes
on either side the uterus. They extend out
from the uterus like arms reaching for the
ovaries which are positioned near them.
Each tube has two openings. One opening
connects to the uterus. The other opening is larger and wider and has a number of
finger-like projections all around it called
the ‘fimbriae’. The fimbriae lie near the ovary of the
same side and picks up the ovum at the
time it is released from the ovary
(‘ovulation’). Microscopic hairs called cilia line the inner side of the tube and help in
propelling the ovum towards the uterus. Each tube is about 10cms long. The width
varies at different parts along the length,
being more towards the ovarian side and
thinner but more muscular towards the
uterine side. Its widest part, the ampulla
lies next to the fimbria and its importance lies in the fact that fertilization of the ovum by the sperm usually occurs in this region. The fallopian tubes are also the
commonest site where blockage can
occur leading to infertility.

MALE SPERM

The Male Reproductive System This consists of the testis, epididymis, genital ducts, accessory glands and the penis. The Testis These are small, paired, oval structures in the scrotum, weighing about 15 g. Like the ovary, the functions of the testes are: 1. Gametogenesis. This equates to the production of sperm in the male, and is called spermatogenesis. The optimum temperature for spermatogenesis is about 2 degrees below body temperature. Factors contributing to temperature control include: The dartos muscle of the scrotum that pulls the testis closer to the body when it
is cold; The pampiniform plexus of veins surrounding the testicular artery, providing a countercurrent heat exchange system whereby cooler venous blood returning from the scrotum and
testis cools the incoming arterial blood. The production of androgens, namely the steroid hormone testosterone. These steroid hormones are essential for
development of the male foetus, development of secondary sex characteristics in puberty, and the maintenance of sperm production in the adult male. Structure of the Testis The structure of the testes consists of: 1. A thick connective tissue capsule: the tunica albuginea, with inwardly projecting septa, creating about 250 lobules. Posteriorly, it thickens and projects inwards to form the mediastinum testes, through which structures enter and leave
the testes. Beneath this layer, a looser tunica vasculosa contains blood vessels. The tunica albuginea is a visceral peritoneal layer that is surrounded anteriorly by a parietal layer called the tunica vaginalis, with a peritoneal sac between them. Inner lobules containing long, highly convoluted seminiferous tubules, surrounded by interstitial (Leydig) cells in the stroma. The tubules straighten out into tubuli recti (straight tubules) before joining an anastomosing channel system in the
mediastinum called the rete testis. Leydig (interstitial) Cells These are large, polygonal, acidophilic cells in the stroma of the lobules. They may contain lipid droplets and cytoplasmic crystals (of Reinke). Leydig cells secrete the androgen testosterone that will act inside the seminiferous tubule. Seminiferous Tubules These tubules are about 50 cm long. They have a complex, stratified, seminiferous epithelium with 2 cell types: 1. Spermatogenic cells organised as patches of cells in different stages of evolution throughout the tubule. As they mature, they move inwards from the basal lamina (spermatogonia) to the lumen (spermatids). 2. Sertoli cells. These are columnar, non- dividing, sustentacular cells on the basal lamina, with an ovoid or triangular nucleus. Sertoli cells maintain the overall structure of the tubules and each support a small colony of developing sperm, surrounding them with cytoplasmic processes. They are bound to each other by Sertoli- Sertoli junctional complexes that form tight junctions. This divides the seminiferous epithelium
into 2 compartments: 1. A basal compartment containing immature spermatogonia and primary spermatocytes; 2. A luminal compartment containing mature spermatocytes and spermatids. It is also the site of the blood-testis barrier, protecting the antigenically foreign haploid sperm from an autoimmune response by circulating antibodies. The Sertoli cells have an exocrine function, secreting fluid for the passage of sperm, and an endocrine function, including the secretion of: 1. Androgen Binding Protein (ABP), that concentrates testosterone in the tubular lumen for the developing sperm; 2. Inhibin is involved with feedback inhibition of FSH from the anterior pituitary. Sertoli cells themselves are stimulated by FSH and testosterone. The seminiferous epithelium is surrounded by lamina propria called tunica propria. This contains peritubular contractile cells (myoid cells). These cells create peristaltic waves that propel spermatozoa and testicular fluid toward the excurrent ducts and epididymis. There are 6 different stages or phases of differentiation of human spermatogonia, called the cycle of the seminiferous epithelium. The total time required for
spermatogonia to reach the stage where
they are released as sperm is 74 days. The patch-like distribution of the stages of differentiation along the tubule is called the wave of the seminiferous epithelium. Back to top Spermatogenesis This is the process by which 1 spermatogonia develops into 4 spermatozoa (sperm). It has 3 distinct phases, the spermatogonial phase, the spermatocyte phase, and the spermatid phase. The Spermatogonial Phase Spermatogonia lie in the basal region of the seminiferous tubule with the Sertoli cells, and have large, rounded nuclei. Dark type A (Ad) spermatogonia give rise to pale type A (Ap) spermatogonia that are connected by cytoplasmic bridges. This ensures synchronous development of each clone. After several divisions, type A cells differentiate into type B spermatogonia. The Spermatocyte Phase (Meiosis) Type B spermatogonia divide into primary spermatocytes by mitosis. Spermatocytes are characterised by prominent nucleoli, due to cell division. The primary spermatocytes undergo meiosis, forming diploid, secondary spermatocytes upon the first meiotic division. Haploid spermatids are formed upon the second meiotic division. The Spermatid Phase (Spermiogenesis) Spermatids lie in the luminal region of the tubule, and may have elongated nuclei. They develop into mature spermatozoa by the process of spermiogenesis, as follows: 1. The acrosomal vesicle forms next to the nucleus at the anterior pole. 2. The acronemal complex (9+2 microtubule arrangement in the tail) begins to be synthesised at the posterior pole. 3. The acrosomal vesicle spreads over the anterior pole, forming the acrosomal cap. 4. Now the nucleus elongates, moving to the front of the cell whilst the cytoplasm extends backwards into the tail. 5. Finally, the cytoplasm is lost into the tubule, becoming a residual body that is phagocytosed by Sertoli cells. 6. The sperm, now free of the Sertoli cell, has a head (5 micrometres), neck (5 micrometres) and tail (50 micrometres). 7. Final maturation of the sperm occurs in
the tail of the epididymis. Sperm are stored in the distal portion of the ductus epididymis before ejaculation. They can live in the male excurrent system for several weeks, but will only survive for 2-3 days in the female reproductive tract. During this time, they will acquire the ability to fertilise the ovum via capacitation. This involves the removal and replacement of the glycocalyx components on the sperm membrane. Back to top Intratesticular Ducts Terminal sections of the seminiferous tubules straighten into tubuli recti (straight tubules), lined only by Sertoli cells. The tubuli recti then narrow, and become lined with simple cuboidal epithelium that is continuous with the rete testis of the mediastinum. Cells in the rete testis have a single apical cilium and few apical microvilli. Excurrent Duct System This consists of : 1. Efferent ductules (ductuli efferentes); 2. The ductus epididymis; 3. The ductus deferens. Efferent Ductules About 20 efferent ductules join the rete testis to the proximal portion of the ductus epididymis. Outside the rete testis, these ducts are highly coiled, forming coni vasculosi that drain into the ductus epididymis. Efferent ductules are lined by a pseudostratified columnar epithelium, with tall columnar ciliated cells and short, non-ciliated cells with numerous microvilli. This gives the lumen a "cog-wheel" appearance. Ductus Epididymis This is the duct of the epididymis, lying posterior to the testis. It has a head, body and tail. Sperm acquire motility and undergo capacitation here. It is lined by pseudostratified columnar epithelium, containing 3 types of cells: 1. Tall principal cells with numerous, long stereocilia; 2. Small, round stem cells on the basal lamina, called basal cells; 3. Intraepithelial lymphocytes called halo cells. The epididymal cells in the proximal portion reabsorb fluids and residual bodies that were not collected by the efferent ductules. They also secrete substances aiding the maturation of sperm. A thin circular smooth muscle layer in the head of the epididymis thickens towards the tail, adding inner and outer longitudinal layers. Mature sperm are stored in the tail. In ejaculation, the 3 smooth muscle layers force the sperm into the ductus deferens. Ductus Deferens This is the terminal portion of the excurrent duct system. It is continuous with the tail of the epididymis. It ascends in the spermatic cord through the scrotum and inguinal canal and enters the abdomen. It then descends to the pelvis and ends in the prostatic urethra. Here it enlarges, forming the ampulla, and is joined by the duct of the seminal vesicle, continuing as the ejaculatory duct through the prostate gland. This opens into the urethra. Like the ductus epididymis, it is lined by pseudostratified columnar epithelium with tall columnar cells and rounded basal cells. Its lumen is dwarfed by a very thick muscular coat that contracts during ejaculation. Back to top Accessory Sex Glands These include: 1. The seminal vesicles; 2. The prostate gland; 3. And the bulbourethral glands. The Seminal Vesicles These are paired, highly folded tubular glands with a muscular and fibrous coat. Mucosal folds create many sac chambers in the lumen. They have pseudostratified columnar epithelium that is similar to that of the excurrent ducts. Its secretory products, under the control of testosterone, include fructose, which is the principal metabolite for sperm. During ejaculation, contraction of the smooth muscle coat discharges the secretions into the ejaculatory ducts and helps flush sperm into the urethra. The Prostate Gland This is the largest accessory gland, consisting of 30-50 tubuloalveolar glands arranged in 3 concentric layers: 1. A mucosal layer, secreting directly into the urethra; 2. A submucosal; 3. And peripheral layer. The last two layers, with the main prostatic glands, open into prostatic sinuses on either side of the urethral crest in the prostatic urethra. The epithelium of the prostate is generally columnar, although it contains cuboidal, squamous and pseudostratified compartments. It is under the control of testosterone. It secretes acid phosphatase, fibrinolysin and citric acid. During ejaculation, these secretions are pumped into the urethra by contraction of the fibromuscular wall. In older men, prostatic alveoli may contain prostatic concretions (corpora amylacea). These are precipitated secretory materials appearing as concentric lamellated bodies. Bulbourethral Glands The bulbourethral glands (Cowper's
glands) are pea-sized, paired structures. They are compound tubuloalveolar glands in the urogenital diaphragm, resembling mucous secretory glands. Their ducts pass through the inferior fascia of the urogenital diaphragm (superficial fascia) to join the initial portion of the penile urethra. Its simple columnar epithelium, also under the control of testosterone, secretes a mucoid fluid that lubricates the penile urethra. Back to top Semen Semen is the combined product of all the glandular elements of the male reproductive system. It: 1. Contains fluid and sperm from the testis; 2. Contains secretions from the epididymis, ductus deferens, prostate, seminal vesicles and bulbourethral glands; 3. Is alkaline, contrasted with the acidic environment of the female vagina. The average volume of ejaculate is about 3 mL. The Penis Structure of the Penis 1. Erectile tissue, including 2 dorsal corpora cavernosa (singular = corpus cavernosum), and a ventral corpus spongiosum in which the penile urethra is embedded; 2. A fibroelastic layer called the tunic albuginea, encapsulating the erectile tissues; 3. An outer layer of loose connective tissue, to which thin skin is loosely attached, except at the glans penis where it attaches tightly; 4. Smooth muscle and many sensory and autonomic nerves are also present. The corpora cavernosa (and, to a lesser extent, the corpus spongiosum) contain many vascular sinuses. In the flaccid penis, helicine (spiral) arteries coil outwards from the centrally located deep arteries of each corpus cavernosum. Blood drains into peripherally located veins. Erection Erection requires 2 conditions: 1. Increased arterial inflow; 2. Decreased venous outflow. The process of erection occurs as follows: 1. Parasympathetic stimulus causes relaxation of the smooth muscle surrounding the vascular endothelium, causing vasodilation of the helicine arteries; 2. The vascular sinuses of the erectile tissue become engorged with blood from increased arterial inflow, and the penis becomes rigid; 3. The transmural pressure rises, compressing the peripheral veins, thus decreasing venous outflow and amplifying the erectile response. Ejaculation Ejaculation occurs via sympathetic stimulus. It involves: 1. Intense contraction of the smooth muscle of the epididymis, ductus deferens, seminal vesicles and prostate; 2. Contraction of the striated muscle in the pelvic and urogenital diaphragms (sphincter utherae) to prevent the passage of urine, and the bulbospongiosus; 3. Emission of the seminal fluid.

FEMALE OVARY

The Female Reproductive
System The female reproductive system consists
of internal organs, including the ovaries, oviducts, uterus and vagina; external genital structures, and the breasts. Menarche, the beginning of menstruation in females after puberty, occurs at about age 15. In the reproductive phase of female life,
the menstrual cycle, taken between each menses (the start of bleeding), lasts about 28 days. Menopause occurs when this cycle eventually ceases, between the ages of 45 and 55. The Ovary These are paired organs lying on either side of the uterus, next to the lateral pelvic wall. There are 2 main functions of the ovary: 1. Gametogenesis: the production of gametes. Oocytes are female gametes developing into mature ova; thus this process is known as oogenesis in the female. 2. The production of steroid hormones, including: Oestrogens, that promote growth and maturation of the sex organs and mammary glands giving mature female characteristics; Progestogens, that prepare the sex organs (mainly the uterus) for pregnancy, and the mammary glands for lactation. These hormones have an important role
in the menstrual cycle by preparing the uterus for implantation of a fertilised ovum. Ovarian Structure The ovary consists of: The Medulla of the Ovary The medulla, in the central portion It contains loose connective tissue, large blood vessels, lymphatics and nerves. The Cortex of the Ovary The cortex, in the peripheral portion. It comprises the bulk of the tissue. It is lined by a layer of cuboidal germinal epithelium, over a dense connective tissue layer called the tunica albuginea. The primordial germ cells, however, are of extragonadal origin. The cortex contains ovarian follicles in richly cellular connective tissue stroma. Scattered smooth muscle fibres are present. At the hilum, the peritoneal fold of mesovarium is continuous with the medulla. Back to top Follicle development Click here for a diagram of follicular development. The early stages of oogenesis occur during foetal development. All potential eggs are present at birth, arrested in their development at the first meiotic division. During the menstrual cycle, follicular maturation and ovulation continues, but only one oocyte will be released from the ovary. Most oocytes present at birth are lost
through atresia: the death and resorption of immature oocytes. Thus, although there are some 400,000 follicles at birth, only 400 eggs will be ovulated in the reproductive life span. Basic types of ovarian follicle include: 1. Primordial follicles, the earliest stage of development; 2. Growing follicles, including preantral (primary) and small antral (secondary) follicles. 3. Mature, pre-ovulatory (Graafian) follicles. Primordial follicles These appear in the third month of foetal development. They are found in the stroma of the cortex just below the tunica albuginea. They are surrounded by a single layer of squamous follicular cells. The oocyte has a large, eccentric nucleus. Preantral (Primary) Follicles This is the first stage of the growing follicle. The oocyte enlarges, and the surrounding follicular cells proliferate, becoming cuboidal. The zona pellucida, a deeply staining, acidophilic glycoprotein layer is deposited next to the follicular cells by microvilli from the oocyte. The follicular cells then stratify with an outer columnar layer, becoming known as granulosa cells. During this proliferation, surrounding stromal cells form the theca folliculi: a connective tissue sheath with 2 layers: 1. The theca interna, an inner, vascular layer of cuboidal secretory cells with luteinising hormone (LH) receptors, that, upon response to LH, synthesise and secrete androgens; the precursors of oestrogen; 2. The theca externa, an outer layer of connective tissue cells, smooth muscle cells and collagen fibres. A basal lamina separates the granulosa cells from the theca folliculi. In the process of atresia, this membrane thickens and hyalinises to become the glassy membrane. The follicle, about 0.2 mm wide, moves deeper into the cortical stroma. Factors required for oocyte and follicular growth include: 1. Follicle stimulating hormone (FSH); 2. Epidermal growth factor (EGF); 3. Insulin-like growth factor I ( IGF-I); 4. Calcium ions (Ca2+). Antral (Secondary) Follicles These follicles have a fluid filled, crescent shaped cavity, the antrum, containing liquor folliculi. The oocyte, positioned eccentrically, grows no further after reaching a diameter of about 125 micrometres. The granulosa cells surrounding the oocyte form the corona radiata. This is located in the cumulus oophorus, a mound of granulosa cells projecting into the antrum. Pre-ovulatory (Graafian) Follicles The mature follicle has a diameter of about 10 mm. Near this size, the stratum granulosum becomes thinner. Spaces between the granulosa cells widen, and the oocyte with its cumulus cells loosens from the others, preparing for ovulation. The thecal layers become more prominent, with lipid droplets appearing in the cytoplasm of theca interna cells. LH stimulates these cells to release androgens that are transported to the granulosa cells. Here, upon the response to FSH, they are converted to oestrogens. This stimulates the granulosa cells to proliferate, increasing the size of the follicle. Back to top Ovulation This is a hormone-mediated process resulting in the release of the secondary oocyte from the pre-ovulatory follicle . This is due to hormonal changes and enzymatic effects occurring in the middle of the menstrual cycle (day 14). A surge in the release of FSH and LH is induced in the pituitary about 24 hours before ovulation. This triggers resumption of the first meiotic division in the primary oocyte, producing two daughter cells: 1. The secondary oocyte, receiving half the chromatin and most of the cytoplasm; 2. The first polar body, which receives little cytoplasm and degenerates. The granulosa and theca cells then undergo luteinisation and produce progesterone. The second meiotic division begins immediately. The macula pellucida (stigma) is the site of rupture of the follicle, and the secondary oocyte with its granulosa cells is expelled, in the process of division. The oocyte, arrested at metaphase, is transported to the oviduct, where it remains viable for about 24 hours. If fertilisation occurs, the second meiotic division completes, producing: 1. A mature ovum with the maternal pronucleus containing a set of 23 chromosomes; 2. The second polar body, which degenerates. If fertilisation fails to occur, the oocyte then degenerates. Back to top The Corpus Luteum After ovulation, the follicle collapses, forming the corpus luteum. Connective tissue eventually invades the follicular lumen, and the granulosa and theca interna cells (luteal cells) become larger, filled with yellow lipid droplets. There are now 2 types of luteal cells: 1. Large, centrally located granulosa lutein cells, from the granulosa cells; 2. Smaller peripherally located theca lutein cells, from the theca interna. This structure becomes highly vascularised, secreting progesterone and oestrogens, preparing the endometrium of the uterus for implantation. If fertilisation occurs, the corpus luteum forms the corpus luteum of pregnancy. If fertilisation does not occur, the corpus luteum of menstruation remains active for 14 days before degenerating and forming a white scar called the corpus albicans. The Ovarian Cycle This consists of 3 phases: 1. The follicular phase (days 1-14), where follicles develop under the influence of oestrogen; 2. Ovulation (day 14): rupture of the follicle; 3. The luteal phase, where the corpus luteum produces progesterone before degenerating. Back to top The Oviduct These are paired tubes, also known as Fallopian or uterine tubes. They extend bilaterally from the uterus to the ovaries. It carries the ova from the ovary to the uterus. There are 4 parts to the oviduct: 1. The funnel-shaped infundibulum opening into the peritoneal cavity next to the ovary with fringed extensions, called fimbriae, extending towards it; 2. The ampulla, the main part of the tube, which is the site of fertilisation; 3. The narrow isthmus, adjacent to the uterus; 4. The uterine or intramural part within the uterine wall; The Wall of the Oviduct This is composed of 3 layers: 1. An external serosa or peritoneum, consisting of mesothelium and loose connective tissue; 2. The intermediate muscularis, consisting of thick, inner circular and thin, outer longitudinal muscle; 3. The inner mucosa, with thin longitudinal folds projecting into the lumen of the oviduct, numerous in the
ampulla, but smaller in the isthmus. There is no submucosa. The simple, columnar epithelial mucosal lining has 2 types of cells: 1. Ciliated cells whose wave is directed toward the uterus; 2. Non-ciliated peg cells that secrete oviductal fluid, providing nutrients for the ovum. Oviduct Transport At ovulation, the fimbriae are closely apposed to the ovarian surface where rupture will occur. As the egg is released, ciliated cells in the infundibulum sweep it towards the oviduct, to prevent it from passing into the peritoneal cavity. The egg is transported to the uterus for about 3 days by both peristaltic muscular activity and ciliary movement. Back to top The Uterus This is a hollow pear-shaped organ with a thick muscular wall. It is divided into: 1. The large upper body, with the fundus above the uterine tubes; 2. The lower, barrel-shaped cervix is separated from the body by the isthmus. The uterine wall is composed of a mucosa, the endometrium; a muscularis, the myometrium; and an external serosa of visceral peritoneum called the perimetrium. There is no submucosa. The myometrium and endometrium undergo cyclic changes each month, constituting the menstrual cycle. The Myometrium This is the thickest layer of the uterine wall. It consists of 3 indistinct layers of muscle: 1. A middle muscle layer, the stratum vasculare, containing large blood vessels, with spiralling, interlacing smooth muscle fibres; 2. Outer and inner layers with smooth muscle fibres running down the long axis of the uterus. In pregnancy, these muscle fibres hypertrophy and divide, and there is an increase in connective tissue. There are elastic fibres in the outer layer. The Endometrium This layer proliferates, then degenerates during the menstrual cycle. It has 2 layers: 1. The thick stratum functionale. It is lined with simple columnar epithelium that invaginates into the endometrial stroma
to form simple, tubular uterine glands. This layer is sloughed off at menstruation; 2. The basal stratum basale, retained during menstruation, serves as a source for regeneration of the stratum functionale. Endometrial Vasculature Arcuate arteries in the myometrium, from the uterine artery, branch to radial arteries entering the basal layer of the endometrium. These branch into straight arteries supplying this layer, and spiral arteries supplying capillaries in the stratum functionale. This capillary bed contains dilated segments called lacunae. The vasculature in this layer proliferates under the influence of oestrogen, and degenerates under the influence of progesterone. Back to top The Menstrual Cycle Click here for a diagram of the menstral cycle. This 28 day cycle has 3 continuous phases: 1. Menstrual phase (days 1-5), when the corpus luteum degenerates and ovarian hormone production declines. In the stratum functionale, arteries constrict and rupture, surface epithelium is disrupted, constituting vaginal discharge; 2. Proliferative phase (days 5-14), influenced by oestrogen from the ovaries, occurring with follicular maturation. Cells and spiral arteries of the stratum basale proliferate rapidly. 3. Secretory phase (days 15-28). This stage begins with ovulation, with the endometrium swelling under the influence of progesterone from the corpus luteum. The Cervix The cervix has 2 constricted openings: 1. The internal os at the uterine end 2. The external os at the vaginal end. This is the site of transition between vaginal stratified squamous epithelium in the porto vaginalis, and the mucous secreting simple columnar epithelium of the cervical canal. The cervical mucosa differs from the rest of the uterine endometrium. It: 1. Lacks spiral arteries; 2. Has little change in thickness over the menstrual cycle, and is not sloughed in the menstrual phase; 3. Have large, branched, mucous secreting cervical glands (Nabothian glands). Normally in the menstrual cycle, the mucous inhibits sperm migration, but during midcycle, a lot less viscous mucous is produced, providing a more favourable environment for the passage of sperm and fertilisation. The cervical epithelial cells are constantly exfoliated into the vagina. These cells can be prepared on a Papanicolaou cervical smear for screening of lesions related to cervical cancer. Back to top The Vagina This is a fibromuscular tube extending from the cervix to the vestibule. The vaginal wall consists of: 1. The vaginal mucosa internally, lined by non-keratinised stratified squamous
epithelium, with many rugae. Connective tissue papillae from the
lamina propria project into this layer.
There are no glands here, as the vagina is lubricated by mucous produced by the cervical glands. 2. The intermediate vaginal muscularis, with inner circular smooth muscle and outer longitudinal fibres. 3. The outer vaginal adventitia, with an inner layer of dense fibroelastic tissue, and an outer layer of loose connective tissue. The Mammary Glands (Breasts) These are modified apocrine sweat glands that develop during puberty. It is composed of lobes of branched (lobulated) tubuloalveolar glands in subcutaneous tissue, radiating from the nipple. Each lobule drains into ducts that carry milk to lactiferous sinuses beneath the areola, where it pools before being secreted through the nipple via lactiferous ducts. The intralobular connective tissue is loose. The dense interlobular connective tissue contains adipose tissue. The areola becomes pigmented during puberty, increasing after pregnancy. It contains sebaceous glands, sweat glands, and modified mammary glands (of Montgomery). Underlying smooth muscle fibres are arranged circumferentially and radially, and longitudinally along the lactiferous ducts. This facilitates lactation from, and erection of the nipple. The nourishing, yellow pre-milk released temporarily after childbirth, colostrum, contains many antibodies that provide the newborn with some passive immunity.

EARLY DEVELOPMENT

The First Week The process of fertilisation occurs as follows: a spermatazoon encounters a receptor protein in the zona pelucida of an oocyte, penetrating this layer by releasing degradative acrosomal
enzymes. The cell membranes of the 2 gametes
fuse, causing: 1. The release of cortical granules from under the oocyte membrane that will
render the zona pellucida impenetrable
to further sperm, preventing polyspermy 2. The oocyte to resume its second meiotic division, becoming the definitive oocyte, and the male and female pronuclei fuse to produce a single, diploid (2N) nucleus of the fertilised zygote. Over the next few days, the zygote, travelling down the oviduct, will undergo cleavage to produce blastomeres, still enclosed in the zona pellucida, and by day 4 consists of about
32 cells, now known as the morula. At about the 8 cell stage, the blastomeres develop an inside-outside
polarity, undergoing compaction to maximise cell to cell contact, and segregation occurs between the central and peripheral blastomeres, forming the inner cell mass and outer cell mass, respectively. The inner cell mass will give rise to most of the embryo proper, and is thus
known as the embryoblast, whilst the outer cell mass will contribute to the
placenta and is called the trophoblast. By day 5, fluid absorbed by the morula forms the blastocyst cavity, so the embryo is now called the blastocyst, and the embryoblast cell mass at one side of
this cavity forms the embryonic pole, with the opposite side being the abembryonic pole. The morula reaches the uterus by about day 4, hatches from the zona pellucida by
day 5, adheres to the uterine lining, and implants in the uterine wall on about day 6.The adjacent endometrial cells respond to the presence of the blastocyst and
progesterone secreted by the corpus
luteum by undergoing the decidual reaction to differentiate into secretory decidual cells, whilst the uterine wall and its glands become oedematous and vascularised. The supply of progesterone is maintained by cells of the trophoblast
secreting human chorionic gonadotropin (hCG) that supports the corpus luteum. Implantation in an abnormal site, such as
the oviduct or peritoneal cavity results in an ectopic pregnancy. Back to top The Second Week The trophoblast differentiates into: 1. An inner cytotrophoblast surrounding the blasocyst 2. An outer layer of proliferating cells at the
embryonic pole that lose their
membranes to form the syncitiotrophoblast. The embryo becomes completely
implanted in the endometrium by day 9,
via the action of hydrolytic enzymes from
the cytotrophoblast. A small region of endometrium where the blastocyst implanted is filled in by
material called the coagulation plug. By day 8, the embryoblast splits into 2 layers: 1. The epiblast (primitive ectoderm) 2. The hypoblast (primitive endoderm), thus forming the bilaminar germ disc. Within the epiblast, the amniotic cavity develops on day 8, with its fluid
displacing some epiblast cells towards
the embryonic pole that will become amnioblasts of the amniotic membrane. On day 8, cells at the periphery of the
hypoblast migrate over the inner surface
of the cytotrophoblast, forming a thin
layer of extraembryonic endoderm called Heuser’s membrane, with the blasocyst cavity henceforth called the primary yolk sac. Extraembryonic reticulum is then secreted between the Heuser’s
membrane and the cytotrophoblast,
beginning the formation of the chorionic cavity. The developing chorionic cavity comes to be lined by extraembryonic mesoderm, whose origin is uncertain, although it will eventually envelop not
only the yolk sac but the amnion as well,
whilst the extraembryonic reticulum
breaks down into fluid. On day 12, a new wave of hypoblast cells proliferate and migrate outwards,
displacing the primary yolk sac towards
the abembryoinc pole, before it
disintegrates into exocoelomic vesicles that will themselves degenerate, leaving
the new definitive yolk sac as a result. Back to top The Third Week On day 15, the primitive streak develops along the caudal midline of the germ disc,
consisting of the primitive groove extending half way along the embryo,
ending in the primitive pit at its cranial end, surrounded by the primitive node. This establishes the longitudinal axis of the embryo and bilateral symmetry in the future adult. On day 16, gastrulation commences with epiblast cells near the primitive
streak developing pseudopodia that allow them to migrate through the primitive groove into the underlying space between the epiblast and
hypoblast. The first wave of ingressing epiblast cells invades the hypoblast layer,
eventually completely replacing it with a
new layer of cells that becomes the definitive endoderm. Another wave of involuting cells fills the space between the epiblast and the
definitive endoderm, forming the intraembryonic mesoderm. Once these two layers are formed, the epiblast is henceforth known as the ectoderm, and thus the 3 definitive layers of the trilaminar germ disc are all derived from the epiblast. As gastrulation proceeds, the primitive streak retreats caudally, giving rise to a
midline mass of mesoderm called the caudal eminence on day 20, and disappearing by day 26. The ingressing mesoderm differentiates according to its position along the primitive streak (ie. its site of
origin), as cells that migrate through the
primitive pit come to lie in the midline, firstly forming a prechordal plate of compact mesoderm, followed by the
hollow tube of the notochordal process. The notochordal process grows cranially as the primitive streak retreats, becoming complete by day 20, and then
begins to transform into a solid rod. First it fuses with the endoderm, then it opens ventrally from the region of the primitive pit, flattening to form the notochordal plate and just transiently forming the neurenteric canal between the yolk sac and the amniotic cavity. At days 22-24, the notochordal plate detaches from the endoderm back into the mesoderm space, becoming a solid
rod called the notochord. Meanwhile, by day 19, 2 depressions in the ectoderm have fused with underlying
endoderm to form bilaminar membranes: 1. The buccopharyngeal membrane at the cranial end 2. The cloacal membrane at the caudal end By day 17, the mesoderm cells that migrated lateral to the primitive streak begin to condense into: 1. The cylindrical paraxial mesoderm adjacent to the notochordal process 2. The less pronounced intermediate mesoderm lateral to the paraxial mesoderm 3. A flattened sheet of lateral plate mesoderm most laterally This process occurs craniocaudally, and the lateral plate mesoderm then splits
into a further 2 layers: 1. A ventral layer next to the endoderm
called the splanchnopleuric mesoderm 2. A dorsal layer next to the ectoderm called
the somatopleuric mesoderm. As the paraxial mesoderm forms, it becomes faintly segmented into rounded somitomeres, with several pairs developing firstly in the cranial region,
then cervical, thoracic, lumbar, sacral and
coccygeal regions. The somitomeres become further segmented into somites, except for the first 7 pairs, with the first somites
appearing on day 20, and with the
process completed by day 30, with a final
count of about 37 pairs starting from the
occipital region to the embryonic tail. The somites establish the segmental organisation of the body, with the first 4 pairs contributing to the skull; the next 8
pairs contributing to the cervical region;
the next 12 pairs being thoracic somites;
the next 5 pairs being lumbar somites;
followed by 5 sacral, and finally 3
coccygeal somites. The neural plate also begins to develop at day 18, with the epiblast cranial to the
primitive pit thickening in response to inducing substances secreted by the underlying prechordal and notochordal
plates, becoming columnar,
pseudostratified neuroepithelial cells (neuroectoderm). Back to top The Fourth Week The somites develop a central cavity
polulated by core cells, before rupturing on their medial sides, forming: 1. The sclerotome medially, that surrounds the developing notocord and neural tube 2. The dermomyotome that is displaced laterally, and will itself split into: 1. A dermotome 2. A myotome The sclerotome surrounding the
notochord ventrally will develop into vertebral bodies, whilst the dorsal portion surrounding the developing
neural tube will form vertebral arches, under the influence of inducing substances. Abnormal induction of the sclerotomes and neural tube causes spinal defects such as scoliosis from the vertebral body rudiments, or spina bifida from the vertebral arch rudiments. Each sclerotome then splits into cranial and caudal segments, with spinal segmental nerves emerging between this split, and the vertebrae are formed from the fusion of the caudal half of each sclerotome with the cranial half of the next, with the cranial half of the 1 st sclerotome fusing with the occipital
bone. The intervertebral discs then form from the sclerotomes, with their nucleus pulposus core derived from notochord cells. Cartilagenous ribs develop from costal processes on thoracic vertebrae, and by day 45, the first 7 will join with the sternum that developed from 2 ventral sternal bars. The dermotome cells migrate to the surface ectoderm of the corresponding
segmental region to form the dermis, although most of the dermis is derived
from somatopleuric lateral plate
mesoderm. The myotome develops into myogenic cells, splitting to form: 1. A dorsal epimere, that will form the deep muscles of the back 2. A ventral hypomere that will form the anterolateral thoracic and abdominal
wall muscles Myoblasts also invade the limb buds for
limb musculature. Meanwhile, the cephalic end of the embryo begins folding ventrally on day 22, giving rise to the mesencephalic flexure that divides the prosencephalon (forebrain) cranially and rhombencephalon (hindbrain) caudally. The rhombencephalon becomes faintly
segmented into rhombomeres, whilst the narrow caudal portion of the neural
plate (the future spinal cord) lengthens rapidly. Neurulation, the folding of the neural plate into the neural tube, commences with the neural groove acting as a hinge for the 2 neural folds as they rotate around so that their lateral lips fuse
dorsally, enclosing the neural canal, whilst simultaneously detaching from the overlying surface ectoderm as it fuses as well, and sinking into the posterior body wall. There may be several points of fusion,
initially in the occipital area before the canal is continuous, leaving open the cranial and caudal neuropores that will close on days 24 and 26, respectively. Formation of the neural tube caudal to
somite 31 occurs by secondary neurulation, where a solid neural cord derived from the caudal eminence cavitates to join the lumen of the neural
canal, and is complete by week 8. Neural crest cells that originated in the lateral lips of the neural folds detach in a
craniocaudal wave from day 22,
migrating to many different parts of the
body, for differentiation into a variety of
structures. The ventricular layer of cells surrounding the neural canal proliferates to produce
most of the cell types of the future
central nervous system. The 1st wave of proliferation from this layer produces neuroblasts (future neurons) that migrate peripherally to
form an outer mantle layer (the future grey matter of the CNS), which in turn
gives rise to another peripheral layer: the marginal layer (the future white matter of the CNS).

THE PLACENTA

The Placenta The human placenta is of chorioallantoic type, consisting of 2 components: 1. The chorion, or outer layers of the chorionic cavity, including: 1. The syncytiotrophoblast 2. The cytotrophoblast 3. The extraembryonic mesoderm 2. The allantois, containing the umbilical vessels and 3 foetal blood vessels: 2 arteries and 1 vein. It also comes under haemochorial classification, with circulation derived from maternal blood and the chorion and other solid parts being derived from
the foetus. The foetal trophoblast invades the endometrium, breaks down the
endometrial blood vessels into lacunae, and forms villi around them. Thus, the placenta is a materno-foetal unit, with: 1. The foetal portion formed by the chorion (chorionic plate) 2. The maternal portion formed by the decidua basalis (basal plate). The foeto-maternal interface consists of these opposed layers: 1. The chorion frondosum 2. Fibrin 3. The decidua basalis Back to top The decidual cell reaction of the
endometrium After implantation, all but the deepest
layer of endometrium proliferates, and is
called the decidua (decidua graviditas). Stromal cells, under influence of the invading trophoblast, differentiate into large, rounded, glycogen filled decidual cells, whilst the uterine glands enlarge, becoming more coiled, before thinning later in pregnancy. There are 3 regions of the decidua: 1. The decidua basalis, underlying the implantation site. 2. The decidua capsularis, a thin portion between between the implantation site
and the uterine lumen, surrounding the
chorion. 3. The decidua parietalis, including the remaining endometrium of the uterus. As the embryo grows and folds, the amnion rapidly expands, until the chorionic cavity is obliterated, and its surrounding decidua capsularis
eventually fuses with the decidua
parietalis, obliterating the uterine cavity by the 3rd month. Back to top The uteroplacental circulation The placenta begins to develop on day 9, with trophoblastic lacunae opening in the syncitiotrophoblast that anastomose
with nearby maternal sinusoids. Chorionic villi begin to develop with extensions of cytotrophoblast, covered
with syncitiotrophoblast, growing out
into the lacunae between days 11-13,
called primary stem villi. On day 16, extraembryonic mesoderm penetrates the cytotrophoblast core of
the primary stem villi, transforming it
into secondary stem villi. Anchoring villi will reach the maternal endometrium, whilst floating villi will not, floating in the lacunae. By the end of the third week, the
anchoring villi contain differentiated blood vessels, and are called tertiary stem villi, thus establishing the uteroplacental circulation. The cytotrophoblast within the anchoring
villi grows towards the maternal
endometrium, branching to form a trophoblastic shell from neighbouring villi. Villi on the decidua capsularis degenerate
after 8 weeks, producing the thin chorion laeve, whilst the villi adjacent to the decidua basalis grow and branch,
with this thick region becoming known
as the chorion frondosum (villous chorion). There are 2 types of cytotrophoblast cells: 1. Darker syncitiotrophoblast cells that
produce hCG 2. Langhans trophoblastic cells in the villi Cells of the villi themselves include: 1. Connective tissue fibroblasts (mesoblasts) 2. Hofbauer cells - large cells with vacuoles that act like macrophages, acting to
reshape the villi. There is unusual immunological tolerance of the placenta by the mother; blebs of syncitiotrophoblast break off from the villi into the lacunae, where
they travel via maternal veins to the
lungs where they are taken up by Dust
cells, but there is no immune reaction to
these. Circulation through the embryo and the
villi starts at about day 21, with the intervillous space as the site of exchange of nutrients and waste products between the maternal and
foetal circulatory system. Foetal and maternal blood do not mix, separated by the placental barrier of foetal tissues. Formation of the umbilical cord The umbilicus is formed when the connecting stalk and the vitelline duct are
bound together by the expanding amnion, and consists of 3 umbilical blood vessels with the allantois (of the
connecting stalk), enclosed in
mesenchyme. Deoxygenated foetal blood enters the
placenta via 2 umbilical arteries, derived from the superior vesical arteries,with a
star shaped lumen formed by 3 smooth
muscle layers: Foetal blood runs through capillaries in the villi, where gases and metabolites are exhanged across the placental barrier with maternal blood supplied by spiral endometrial arteries. Oxygentated foetal blood returns from
the placenta via the umbilical vein. Oxygen, water, carbon dioxide,
hormones, vitamins and antibodies can
all cross the placental barrier. Many harmful substances can also cross, including drugs like nicotine and alcohol, and viruses like Rubella, CMV and HIV. Untreated diabetes in the mother, leading to hyperglycemia, leads to high blood glucose across the placental barrier,
thus inducing the foetal pancreas to
secrete insulin, elevating foetal blood insulin and causing enourmous growth of the foetus. The placenta must be removed after birth
and the uterus allowed to contract,
otherwise the spiral arteries will not
close, leading the bleeding and infection. Back to top The placenta as a major
endocrine gland The placenta takes over the corpus luteum from the role of producing the steroid hormones oestrogen and progesterone as pregnancy proceeds; synthesising these hormones in the syncytiotrophoblast. The placenta also secretes several
peptide hormones, including: 1. Human chorionic gonadotropin (hCG) - produced by the syncytiotrophoblast,
with synthesis beginning around day 6
and peaking in the 1st trimester; it is
used to detect pregnancy. 2. Human chorionic somatomammotropin (hCS) or Human placental lactogen (hPL) -
synthesised by the syncitiotrophoblast,
promotes general growth, glucose
metabolism, and late in pregnancy,
stimulates mammary duct development. 3. Insulin-like growth factors I and II (IGF- I, IGF-II) - produced by and stimulate
differentiation of the cytotrophoblast. 4. Endothelial growth factor (EGF) - synthesised by the cytotrophoblast,
stimulates differentiation of the
trophoblast until week 6, after which its
systhesis is shifted to the
syncytiotrophoblast. Back to top Respiration in the placenta Airsac pO2 Arterial pO2 Lung ~100 mmHg ~90 mmHg Placenta ~90 mmHg ~25 mmHg The pO2 of foetal blood leaving the placenta is less than 1/3 of maternal pO2, although it is never short of oxygen. This is because foetal haemoglobin (2 alpha, 2 gamma chains), does not bind 2,3-DPG as well as adult haemoglobin (2 alpha, 2 beta chains), resulting in a higher affinity for oxygen . So, at any given partial pressure, foetal
blood has a higher oxygen saturation
than the mother, and it will tend to "pull
off" oxygen from the adult haemoglobin. Glomerular Filtration Rate changes Non pregnant 100-120 mL/ min Pregnant 150-180 mL/ min

RIXIMKA DUMARKA

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THE INGUINAL REGION

FERTILIZATION

INTERNAL VAGINAL ORGANS

MALE SPERM

FEMALE OVARY

EARLY DEVELOPMENT

THE PLACENTA