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URETHROVESICAL UNIT STRUCTURE AND FUNCTION
The urethrovesical unit consists of the bladder, urethra, and pelvic
muscles; it is also called the lower urinary tract. The urinary bladder
is a muscle-lined sac that stores and empties itself of urine. In the infant
the bladder lies entirely in the abdomen. The bladder assumes its place
in the true pelvis shortly before puberty. This change in position is due
to the maturation of the pelvic bone rather than migration of the
bladder and urethra.
The bladder has two inlets (the ureteral orifices) and a single outlet
(the urethral orifice). The base of the bladder is a relatively fixed, triangular area consisting of the bladder neck and trigone. In contrast,
the body of the bladder is distensible, changing from a tetrahedron (four-sided shape) when relatively empty to a nearly spherical shape
as the bladder fills.
One of the four layers of the bladder wall consists of smooth muscle
bundles that promote bladder evacuation via micturition. Collectively
this muscular tunic is called the detrusor. The muscular tunic of the
bladder wall also contains collagen, a tough, nonelastic substance that
maintains the integrity of the bladder wall while also preventing
overdistention. Certain pathologic factors, including denervation of
the bladder and obstruction of the outlet, may cause an overabundance
of collagen in the detrusor muscle. This causes a loss of bladder compliance…