Bladder Anatomy and Physiology
The urinary bladder lies in the anterior part of the pelvic cavity. When distended, the organ has an approximately spherical shape, but when empty, it assumes the form of a tetrahedron with four angles and four surfaces. The two posterolateral angles receive the ureters while the inferior angle, the bladder neck, is continuous with the urethra. The anterior angle gives attachment to a fibrous cord, the median umbilical ligament (Fig. 5.17). This remnant of the fetal allantois ascends in the extraperitoneal tissues of the anterior abdominal wall to the umbilicus. If it remains patent, urine may leak from the umbilicus.
The superior surface and the two inferolateral surfaces expand considerably as urine accumulates but the comparatively small posterior surface or base remains relatively fixed. This surface lies between the entrances of the ureters and the bladder neck.
The wall of the bladder consists of smooth muscle (detrusor) whose thickness gradually decreases as the organ fills. Although the interior of the distended bladder is smooth, the mucosa becomes rugose when the organ empties (Fig. 5.17), except in the region of the trigone. This is the triangular area between the ureteric orifices and the internal urethral meatus (Fig. 5.14). The ureters pierce the musculature of the bladder wall obliquely and open at slit-like orifices.
The superior surface of the bladder is covered with peritoneum (Fig. 5.17) on which rest coils of ileum and sigmoid colon. In both sexes, the inferolateral surfaces lie against the obturator internus and levator ani muscles and their associated fascial coverings. Between the bladder and these muscles run the obturator nerve and vessels and the superior vesical vessels (Fig. 5.16). Anterior to the bladder is the retropubic space, filled with adipose tissue and veins (Fig. 5.17). The empty bladder lies behind the pubic bones but as it fills, it rises above the level of the pubic crests and comes into contact with the lower part of the anterior abdominal wall. The distended bladder intervenes between the parietal peritoneum and the abdominal wall (Fig. 4.30) and can be accessed through a lower abdominal incision without opening the peritoneum.
In the male, the seminal vesicle and the ampulla of the ductus deferens are applied to each side of the posterior surface.
Peritoneum descends a short distance on this surface before being reflected onto the anterior surface of the rectum to form the rec- tovesical pouch (Fig. 5.14). Below the level of this pouch, the bladder is related to the rectovesical septum and the ampulla of the rectum. Inferior to the male bladder lie the prostate and the prostatic plexus of veins.
In the female, the posterior part of the superior surface of the bladder is related to the body of the uterus (Fig. 5.17). Peritoneum passes from the superior surface of the bladder onto the uterine body, forming the vesicouterine pouch. Against the posterior surface of the female bladder lie the cervix of the uterus and the anterior wall of the vagina. The inferior angle of the bladder in the female lies at a lower level than in the male and is closely related to the two levatorani muscles.
The bladder is supplied by branches of the internal iliac arteries. On each side, the patent part of the umbilical artery gives off one or more superior vesical arteries (Fig. 5.16). The bladder receives additional supply from the inferior vesical and obturator arteries. In the female, the uterine and vaginal arteries also contribute to the vascular supply of the bladder.
Venous blood passes into an extensive network of veins, the vesical plexus, which communicates with the prostatic or vaginal plexus and drains into the internal iliac veins.
The motor innervation to the detrusor muscle is by parasympathetic nerves conveyed in the pelvic splanchnic nerves and the pelvic plexus of autonomic nerves (Fig. 5.30). In the male, the smooth muscle surrounding the bladder neck (preprostatic sphincter) is innervated by sympathetic nerves derived from the hypogastric plexus. The parasympathetic motor innervation stimulates contraction of the bladder at the time of micturition, while the sympathetic supply to the male bladder neck prevents reflux during ejaculation.