URINARY BLADDER

The Urinary Bladder The bladder (L. vesica) is a hollow, muscular vesicle for storing urine. In adults, the empty bladder lies in the pelvis minor. It lies posterior and slightly superior to the pubic bones. It is separated from the pubic bones by the retropubic space. As the bladder fills, it ascends into the pelvis major and a very full bladder may ascend to the level of the umbilicus. The bladder is a hollow viscus with strong muscular walls. It is characterised by its distensibility. Its shape, size, position, and relations are dependent with the amount of urine it contains and with the age of the person. The mucous membrane is loosely connected to its muscular wall, except in a triangular region in its base (fundus). This region is known as the trigone of the bladder. The mucous membrane in the empty bladder is in numerous folds or rugae except in the trigone area where it is always smooth (due it its firm
attachment to the muscular wall). Back to top The Form of the Bladder Click here for a schematic of the shape of the urinary bladder. The shape of the bladder in cadavers is
like a tetrahedron (it is more or less rounded in living persons). It has 4 sides, 4 angles and 4 ducts. The Sides of the Bladder The sides include: 1. The base or fundus, which is related to the anterior vaginal wall (females) or the rectum, seminal vesicles and ductus deferens (males); 2. The superior surface; 3. And 2 inferolateral surfaces, which is separated from the pubis and puboprostatic ligament (male) or pubovesical ligament (female) by the retropubic fat pad. The Angles of the Bladder The angles include: 1. The apex, which is continuous with the obliterated urachus (median umbilical ligament); 2. The neck, which is the most inferior part and is related to the prostate (males) or superior pelvic fascia (females); 3. And 2 lateral angles where the ureters enter the bladder. The Ducts of the Bladder The ducts include: 1. The urachus from the apex; 2. The 2 ureters from the lateral angles; 3. And the urethra, which pierces the neck of the bladder. Bladder capacities in the adult male vary from 120 mL to 320 mL, with micturition usually occurring at 280 mL (Ashwell). When the bladder is filled it contains about 500 mL (Moore). Values for females are presumably less. Back to top The Bladder Bed The shape of the bladder is largely determined by the structures that are closely related to it. The entire organ is enveloped by loose connective tissue, called vesicle fascia, in which is located the vesical venous plexus. The bladder bed is formed by: 1. On each side by the pubic bones; 2. The levator ani muscles; 3. The obturator internus muscle; 4. And posterior by the rectum. In the female the base of the bladder is separated from the rectum by the cervix and the superior part of the vagina. The bladder neck lies directly on the pelvic fascia, surrounding the short urethra. In the male, the base of the bladder is separated from the rectum by the ampullae of the ductus deferens and the seminal vesicles. Its neck fuses with the prostate. The Ligaments of the Bladder In both sexes, there are ligaments that extend from the posterior of the pubis to the neck of the bladder. These are the pubovesicle ligaments. These are the superior extensions of the pubourethral ligaments (female) and the puboprostatic ligaments (males). These ligaments lie on either side of the
midline and the small space between
them is for the transmission of small
veins. Lateral and posterior ligaments are described as reflections of peritoneum. They are considered as false ligaments by some authors. The bladder apex is also connected to the umbilicus by the urachus (the median umbilical ligament). The Interior of the Bladder Click here for a diagram of the interior of the bladder. The trigone, which is a smooth area on the interior of the base, is bounded by the internal ureteric orifices (2.5 cm apart in the empty bladder) and the internal urethral orifice. The internal ureteric orifices are joined by the interureteric ridge (or crest). These ridges may extend past the
ureteric openings laterally as the ureteric folds. In adult males, particularly past middle age, there is a slight elevation of the mucosa posterior to the internal urethral orifice. This is known as the uvula and is formed by the median prostatic lobe. In men with an enlarged prostate gland, this uvula may obstruct the internal urethral orifice. Back to top The Arterial Supply of the Urinary
Bladder The main arteries supplying the bladder
are branches of the internal iliac arteries. The superior vesicle artery, branches of the umbilical artery supply the anterosuperior parts of the bladder. The inferior vesicle arteries (in males) or vaginal arteries (in females), branches of the internal iliac arteries, supply the base of the bladder. The obturator and inferior gluteal arteries also supply small branches to the bladder. The Venous Drainage of the Urinary
Bladder The veins from a venous plexus on the inferolateral surface and drain back to the internal iliac vein. The Lymphatic Drainage of the Urinary
Bladder The lymph vessels from the superior part of the bladder pass to the external iliac lymph nodes. Those from the inferior part of the bladder pass the internal iliac lymph nodes. Some lymph vessels from the neck region of the bladder drain into the sacral or common iliac lymph nodes. Innervation of the Urinary Bladder The Efferent Fibres Parasympathetic from the S2-4 segments of the spinal cord (nervi erigentes). These enter the inferior hypogastric plexus and pass through it to the bladder wall. They are motor to the detrusor and inhibitory to the internal sphincter. Sympathetic from the T11-12, L1-2 segments of the spinal cord. These synapse in the inferior hypogastric plexus and the postganglionic fibres pass to the bladder. They cause constriction in the internal sphincter and inhibit the detrusor muscle. The Afferent Fibres These are concerned with the awareness of distension and pain. They pass back to the CNS via both the sympathetic and parasympathetic nerves. Back to top The Urethra The Male Urethra In the male, the urethra is about 18-20 cm long and it extends from the internal urethral orifice in the bladder to the external meatus on the tip of the penis. It may be divided into 4 parts: the preprostatic, prostatic, membranous and spongiose. The Preprostatic Part This part possesses a stellate lumen and is only 1.5 cm long. It extends from the internal urethral orifice to the superior aspect of the prostate. Smooth muscle surrounding the bladder neck and preprostatic urethra is circular and is known as the internal sphincter (sphincter vesicae). This is richly supplied with sympathetic noradrenergic fibres. The Prostatic Part This is 3-4 cm long and has a midline ridge on its posterior wall known as the urethral crest. On each side of the crest is a groove known as the prostatic sinus, into which the orifices of the prostatic ducts open. There is an elevation on the urethral crest about halfway down which is known as the collicus seminalis (verumontanum). On the summit of this, the prostatic utricle opens. The prostatic utricle is 6 mm long and is the remnant of the paramesonephric ducts. On either side of the utricle are the openings of the ejaculatory ducts. The Membranous Part This is the shortest part (2 cm) and the least dilatable part and passes through the urogenital diaphragm. The external sphincter or sphincter urethrae is derived from the urogenital diaphragm musculature. The sphincter urethrae is supplied by the perineal branches of the pudendal nerve (S2-4). The Spongiose Part This part is contained within the corpus spongiosum of the penis. It is dilated at its beginning as the intrabulbar fossa, and again within the glans of the penis as the navicular fossa. The ducts of the bulbourethral gland opens into the spongiose part below the perineal membrane. The external urethral orifice is the narrowest part of the urethra. There are several recesses in the urethra known as lacunae. Mucous glands known as urethral glands open into this part of the urethra. The Female Urethra The female urethra is only 4 cm long and opens at the external urethral orifice. This is about 2.5 cm behind the glans clitoris and directly in front of the vaginal opening. The female urethra has a posterior longitudinal fold (as known as the urethra crest). Similarly, it also has external and internal sphincters. The Stages of Micturition 1. Pubovaginalis (female) and levator prostatae (male), parts of the pubococcygeus muscle; 2. The bladder neck drops; 3. The downward movement initiates contraction of the detrusor and relaxation of the sphincter vesicae (parasympathetic reflex arcs); 4. Somatic nerves (S2-4) relax the external urethral sphincters; 5. The urine passes outwards.The Urinary Bladder The bladder (L. vesica) is a hollow, muscular vesicle for storing urine. In adults, the empty bladder lies in the pelvis minor. It lies posterior and slightly superior to the pubic bones. It is separated from the pubic bones by the retropubic space. As the bladder fills, it ascends into the pelvis major and a very full bladder may ascend to the level of the umbilicus. The bladder is a hollow viscus with strong muscular walls. It is characterised by its distensibility. Its shape, size, position, and relations are dependent with the amount of urine it contains and with the age of the person. The mucous membrane is loosely connected to its muscular wall, except in a triangular region in its base (fundus). This region is known as the trigone of the bladder. The mucous membrane in the empty bladder is in numerous folds or rugae except in the trigone area where it is always smooth (due it its firm
attachment to the muscular wall). Back to top The Form of the Bladder Click here for a schematic of the shape of the urinary bladder. The shape of the bladder in cadavers is
like a tetrahedron (it is more or less rounded in living persons). It has 4 sides, 4 angles and 4 ducts. The Sides of the Bladder The sides include: 1. The base or fundus, which is related to the anterior vaginal wall (females) or the rectum, seminal vesicles and ductus deferens (males); 2. The superior surface; 3. And 2 inferolateral surfaces, which is separated from the pubis and puboprostatic ligament (male) or pubovesical ligament (female) by the retropubic fat pad. The Angles of the Bladder The angles include: 1. The apex, which is continuous with the obliterated urachus (median umbilical ligament); 2. The neck, which is the most inferior part and is related to the prostate (males) or superior pelvic fascia (females); 3. And 2 lateral angles where the ureters enter the bladder. The Ducts of the Bladder The ducts include: 1. The urachus from the apex; 2. The 2 ureters from the lateral angles; 3. And the urethra, which pierces the neck of the bladder. Bladder capacities in the adult male vary from 120 mL to 320 mL, with micturition usually occurring at 280 mL (Ashwell). When the bladder is filled it contains about 500 mL (Moore). Values for females are presumably less. Back to top The Bladder Bed The shape of the bladder is largely determined by the structures that are closely related to it. The entire organ is enveloped by loose connective tissue, called vesicle fascia, in which is located the vesical venous plexus. The bladder bed is formed by: 1. On each side by the pubic bones; 2. The levator ani muscles; 3. The obturator internus muscle; 4. And posterior by the rectum. In the female the base of the bladder is separated from the rectum by the cervix and the superior part of the vagina. The bladder neck lies directly on the pelvic fascia, surrounding the short urethra. In the male, the base of the bladder is separated from the rectum by the ampullae of the ductus deferens and the seminal vesicles. Its neck fuses with the prostate. The Ligaments of the Bladder In both sexes, there are ligaments that extend from the posterior of the pubis to the neck of the bladder. These are the pubovesicle ligaments. These are the superior extensions of the pubourethral ligaments (female) and the puboprostatic ligaments (males). These ligaments lie on either side of the
midline and the small space between
them is for the transmission of small
veins. Lateral and posterior ligaments are described as reflections of peritoneum. They are considered as false ligaments by some authors. The bladder apex is also connected to the umbilicus by the urachus (the median umbilical ligament). The Interior of the Bladder Click here for a diagram of the interior of the bladder. The trigone, which is a smooth area on the interior of the base, is bounded by the internal ureteric orifices (2.5 cm apart in the empty bladder) and the internal urethral orifice. The internal ureteric orifices are joined by the interureteric ridge (or crest). These ridges may extend past the
ureteric openings laterally as the ureteric folds. In adult males, particularly past middle age, there is a slight elevation of the mucosa posterior to the internal urethral orifice. This is known as the uvula and is formed by the median prostatic lobe. In men with an enlarged prostate gland, this uvula may obstruct the internal urethral orifice. Back to top The Arterial Supply of the Urinary
Bladder The main arteries supplying the bladder
are branches of the internal iliac arteries. The superior vesicle artery, branches of the umbilical artery supply the anterosuperior parts of the bladder. The inferior vesicle arteries (in males) or vaginal arteries (in females), branches of the internal iliac arteries, supply the base of the bladder. The obturator and inferior gluteal arteries also supply small branches to the bladder. The Venous Drainage of the Urinary
Bladder The veins from a venous plexus on the inferolateral surface and drain back to the internal iliac vein. The Lymphatic Drainage of the Urinary
Bladder The lymph vessels from the superior part of the bladder pass to the external iliac lymph nodes. Those from the inferior part of the bladder pass the internal iliac lymph nodes. Some lymph vessels from the neck region of the bladder drain into the sacral or common iliac lymph nodes. Innervation of the Urinary Bladder The Efferent Fibres Parasympathetic from the S2-4 segments of the spinal cord (nervi erigentes). These enter the inferior hypogastric plexus and pass through it to the bladder wall. They are motor to the detrusor and inhibitory to the internal sphincter. Sympathetic from the T11-12, L1-2 segments of the spinal cord. These synapse in the inferior hypogastric plexus and the postganglionic fibres pass to the bladder. They cause constriction in the internal sphincter and inhibit the detrusor muscle. The Afferent Fibres These are concerned with the awareness of distension and pain. They pass back to the CNS via both the sympathetic and parasympathetic nerves. Back to top The Urethra The Male Urethra In the male, the urethra is about 18-20 cm long and it extends from the internal urethral orifice in the bladder to the external meatus on the tip of the penis. It may be divided into 4 parts: the preprostatic, prostatic, membranous and spongiose. The Preprostatic Part This part possesses a stellate lumen and is only 1.5 cm long. It extends from the internal urethral orifice to the superior aspect of the prostate. Smooth muscle surrounding the bladder neck and preprostatic urethra is circular and is known as the internal sphincter (sphincter vesicae). This is richly supplied with sympathetic noradrenergic fibres. The Prostatic Part This is 3-4 cm long and has a midline ridge on its posterior wall known as the urethral crest. On each side of the crest is a groove known as the prostatic sinus, into which the orifices of the prostatic ducts open. There is an elevation on the urethral crest about halfway down which is known as the collicus seminalis (verumontanum). On the summit of this, the prostatic utricle opens. The prostatic utricle is 6 mm long and is the remnant of the paramesonephric ducts. On either side of the utricle are the openings of the ejaculatory ducts. The Membranous Part This is the shortest part (2 cm) and the least dilatable part and passes through the urogenital diaphragm. The external sphincter or sphincter urethrae is derived from the urogenital diaphragm musculature. The sphincter urethrae is supplied by the perineal branches of the pudendal nerve (S2-4). The Spongiose Part This part is contained within the corpus spongiosum of the penis. It is dilated at its beginning as the intrabulbar fossa, and again within the glans of the penis as the navicular fossa. The ducts of the bulbourethral gland opens into the spongiose part below the perineal membrane. The external urethral orifice is the narrowest part of the urethra. There are several recesses in the urethra known as lacunae. Mucous glands known as urethral glands open into this part of the urethra. The Female Urethra The female urethra is only 4 cm long and opens at the external urethral orifice. This is about 2.5 cm behind the glans clitoris and directly in front of the vaginal opening. The female urethra has a posterior longitudinal fold (as known as the urethra crest). Similarly, it also has external and internal sphincters. The Stages of Micturition 1. Pubovaginalis (female) and levator prostatae (male), parts of the pubococcygeus muscle; 2. The bladder neck drops; 3. The downward movement initiates contraction of the detrusor and relaxation of the sphincter vesicae (parasympathetic reflex arcs); 4. Somatic nerves (S2-4) relax the external urethral sphincters; 5. The urine passes outwards.