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.
Blood supply
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.
Nerve supply
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.
