The term sperm is derived from the Greek word (σπέρμα) sperma (meaning "seed")
and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or
sperm cell. The human sperm cell is haploid, so that its 23 chromosomes can join the 23
chromosomes of the female egg to form a diploid cell. A uniflagellar sperm cell that is motile is referred to as a spermatozoon, whereas a non-motile sperm cell is
referred to as a spermatium. Sperm cells cannot divide and have a limited life span,
but after fusion with egg cells during fertilization, a new organism begins
developing, starting as a totipotent zygote.[citation needed] The spermatozoa of animals are produced through spermatogenesis inside the male gonads (testicles) via meiotic division. They are carried out of the male body in a
fluid known as semen. Mammalian sperm cells can survive within the female
reproductive tract for more than 5 days post coitus.[1] Sperm cells in algal and many plant gametophytes are produced in male gametangia (antheridia) via mitotic division. In flowering plants, sperm nuclei are produced inside pollen.[citation needed] Etymology The term "sperm" probably comes from
sperma which in Greek is "seed" or Latin
"something sown". Other terms for sperm
include "prostatic fluid" and "seminal fluid"
and "seed". Origin Sperm originates solely from the testicles, and this is where sperm develop. The
initial spermatozoon process takes around 70 days to complete. The spermatid stage is where the sperm develops the familiar
tail. The next stage where it becomes fully
mature takes around 60 days when its called a spermatozoan.[2] Subsequently, the semen wherein the sperm is carried is produced in the seminal vesicles, prostate gland and urethral glands. AnatomySperm fertilizing an egg The sperm cell consists of a head, a
midpiece and a tail. The head contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an acrosome, which contains enzymes used for penetrating the female egg. The
midpiece has a central filamentous core
with many mitochondria spiralled around
it, used for ATP production for the journey through the female cervix, uterus and uterine tubes. The tail or "flagellum" executes the lashing movements that propel the spermatocyte.[citation needed] During fertilization, the sperm provides three essential parts to the oocyte: (1) a signalling or activating factor, which
causes the metabolically dormant oocyte to activate; (2) the haploid paternal genome; (3) the centrosome, which is responsible for maintaining the microtubule system.[3] Motile sperm cells Motile sperm cells of algae and seedless plants.[4] Motile sperm cells typically move via flagella and require a water medium in order to swim toward the egg for
fertilization. Most of the energy for sperm
motility is derived from the metabolism of fructose carried in the seminal fluid. This takes place in the mitochondria located in the sperm's midpiece (at the base of the
sperm head). These cells cannot swim
backwards due to the nature of their
propulsion. The uniflagellated sperm cells
(with one flagellum) produced in most animals are referred to as spermatozoa, and are known to vary in size.[citation needed] Motile sperm are also produced by many protists and the gametophytes of bryophytes , ferns and some gymnosperms such as cycads and ginkgo. The sperm cells are the only flagellated cells in the life
cycle of these plants. In many ferns and lycophytes , they are multi-flagellated (carrying more than one flagellum).[4] In nematodes, the sperm cells are amoeboid and crawl, rather than swim, towards the egg cell.[5] Non-motile sperm cells Non-motile sperm cells called spermatia lack flagella and therefore cannot swim.
Spermatia are produced in a spermatangium.[4] Because spermatia cannot swim, they
depend on their environment to carry them
to the egg cell. Some red algae, such as Polysiphonia, produce non-motile spermatia that are spread by water currents after their release.[4] The spermatia of rust fungi are covered with a sticky substance. They are produced in
flask-shaped structures containing nectar, which attract flies that transfer the spermatia to nearby hyphae for fertilization in a mechanism similar to insect pollination in flowering plants.[6] Fungal spermatia (also called pycniospores,
especially in the Uredinales) may be
confused with conidia. Conidia are spores that germinate independently of
fertilization, whereas spermatia are gametes that are required for fertilization. In some fungi, such as Neurospora crassa, spermatia are identical to microconidia as
they can perform both functions of
fertilization as well as giving rise to new organisms without fertilization.[7] Sperm nuclei In many land plants, including most gymnosperms and all angiosperms, the male gametophytes (pollen grains) are the primary mode of dispersal, for example via wind or insect pollination, eliminating the need for water to bridge the gap between
male and female. Each pollen grain
contains a spermatogenous (generative)
cell. Once the pollen lands on the stigma of a receptive flower, it germinates and
starts growing a pollen tube through the carpel. Before the tube reaches the ovule, the nucleus of the generative cell in the
pollen grain divides and gives rise to two
sperm nuclei which are then discharged
through the tube into the ovule for fertilization.[4] In some protists, fertilization also involves sperm nuclei, rather than cells, migrating toward the egg cell through a fertilization
tube. Oomycetes form sperm nuclei in a syncytical antheridium surrounding the egg cells. The sperm nuclei reach the eggs
through fertilization tubes, similar to the pollen tube mechanism in plants.[4] Sperm quality Human sperm stained for semen quality testing. Main article: Semen quality Sperm quantity and quality are the main parameters in semen quality, which is a measure of the ability of semen to accomplish fertilization. Thus, in humans, it is a measure of fertility in a man. The genetic quality of sperm, as well as its
volume and motility, all typically decrease with age.[8] (See paternal age effect.) Market for human sperm Further information: Sperm donation On the global market, Denmark has a well- developed system of human sperm export.
This success mainly comes from the
reputation of Danish sperm donors for being of high quality[9] and, in contrast with the law in the other Nordic countries,
gives donors the choice of being either
anonymous or non-anonymous to the receiving couple.[9] Furthermore, Nordic sperm donors tend to be tall and highly educated[10] and have altruistic motives for their donations,[10] partly due to the relatively low monetary compensation in
Nordic countries. More than 50 countries
worldwide are importers of Danish sperm,
including Paraguay, Canada, Kenya, and Hong Kong.[9] However, the Food and Drug Administration (FDA) of the US has banned import of any sperm, motivated by a risk
of mad cow disease, although such a risk is insignificant, since artificial insemination
is very different from the route of transmission of mad cow disease.[11] The prevalence of mad cow disease is one in a million, probably less for donors. If
prevalence was the case, the infectious
proteins would then have to cross the blood-testis barrier to make transmission possible.[11] Transmission of the disease by an insemination is approximately equal
to the risk of getting killed by lightning. [12] History See also: Homunculus#Homunculus of spermists Sperm were first observed in 1677 by Antonie van Leeuwenhoek [13] using a microscope, he described them as being animalcules (little animals), probably due to his belief in preformationism, which thought that each sperm contained a fully formed but small human.[citation needed] Forensic Analysis Ejaculated fluids are detected by ultraviolet light, irrespective of the structure or colour of the surface.[14] Sperm heads, e.g. from vaginal swabs, are
still detected by microscopy using the "Christmas Tree Stain" method, i.e.,
Kernechtrot-Picroindigocarmine (KPIC) staining
UTERUS
FERTILIZATION
CLITORIS
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.
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.
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.
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