Urinary Bladder

Structure
The urinary bladder is a hollow viscus, with strong muscular walls (the detrusor muscle and internal urethral sphincter; involuntary innervated), distinguished for its distensibility. One of the main reasons for its ability to change in volume and size, is the pseudo-stratified transitional epithelial lining in its internal surface and of course the elasticity of the muscular walls. It is covered by the visceral fascia. The internal urethral sphincter is also responsible for preventing reflux of semen (retrograde ejaculation) into the bladder, since it closes the internal urethral orifice during the ejaculation. The uvula of bladder is slight elevation of the trigone, just above the neck. In older men where the posterior prostatic lobe is hypertrophic, the uvula is more prominent.

Divisions

 * 1) Apex.
 * 2) Body – it proceeds upwards towards the vertex, the apex of the bladder.
 * 3) Fundus – it lies posteriorly and is the anterior border of the rectovesical pouch in males and vesicouterine pouch in females.
 * 4) Neck.

Surfaces

 * 1) Superior
 * 2) Inferolateral (left)
 * 3) Inferolateral (right)
 * 4) Posterior

Umbilical ligaments

 * Median umbilical ligament: it is a continuation of the apex and ends to the umbilicus and is the remnant of the embryonic urachus.
 * Lateral umbilical ligaments: they are remnants of embryonic umbilical arteries and ascend from the body of the bladder to the umbilicus.

Ureteric orifices
There are 2 ureteric orifices. They lie at the angles of the trigone of the bladder and they form the interureteric crest. At the inferior angle of the trigone, lies the internal urethral orifice. The openings of the ureteric orifices are encircled by loops of the detrusor musculature, that tighten during bladder contraction, thus preventing reflux of urine back to the ureters.

Position
The urinary bladder is located in the lesser pelvis (after puberty), lying partially superior and partially posterior to the pubic bones. It is separated from the pubic symphysis by the retropubic space and lies mostly inferior to the peritoneum. It is relatively free in the extraperitoneal subcutaneous fatty tissue. When filled, it ascends to the greater pelvis in the extraperitoneal fatty tissued of the anterior abdominal wall. Laterally is held by the lateral vesical ligaments from the neck and the tendinous arch of the pelvic fascia. Anteriorly is held by the puboprostatic ligament (males) and the pubovesical ligament (females).

Arterial supply
All these arteries are branches of the internal iliac artery.
 * Anterosuperior supply: Superior vesical arteries.
 * Fundus & neck (posteroinferior) supply: Inferior vesical arteries in males, and the vaginal arteries in females.

Venous drainage
In males: Vesical venous plexus, is continuous with the prostatic venous plexus, receiving blood from the deep dorsal vein of the penis and both plexuses drain into the inferior vesical veins and then into the internal iliac veins. Possible drainage of the plexuses can be also in the internal vertebral venous plexuses through the sacral veins. In females: Vesical venous plexus that envelopes the pelvic part and neck of the bladder, receives blood from the deep dorsal vein of clitoris and communicates with the (utero)vaginal venous plexus, which in turns drains into the internal iliac vein.

Lymphatic drainage
It is carried out by vessels that pass from the superolateral aspects of the bladder draining into the external iliac lymph nodes and by vessels passing from the neck and fundus draining into the internal iliac lymph nodes and some into the sacral or common iliac lymph nodes.

Innervation

 * Parasympathetic: pelvic splachnic nerves, inferior hypogastric plexus. Motor to the detrusor muscle and inhibitory to the internal urethral sphincter in males.
 * Sympathetic: T11–L2 nerves. Stimulates ejaculation with simultaneous contraction of the internal sphincter urethrae, preventing retrograde ejaculation.
 * Vesical nervous plexus, which communicates with the inferior hypogastric plexus.

Related articles

 * Kidney
 * Uterus
 * Prostate
 * Peritoneal cavity