Bladder Anatomy
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 fetalallantois 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 rectovesical 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 levator ani
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.
