Urinary Bladder is a muscular, membranous, distensible reservoir that holds urine situated in the pelvic cavity. It receives urine from the kidneys through the ureters and discharges it from the body through the urethra.
ANATOMY: The bladder is situated in the anterior inferior portion of the pelvic cavity. In the female it lies in front of the anterior wall of the vagina and the uterus; in the male it lies in front of the rectum.
The lower portion of the bladder, continuous with the urethra, is called the neck; its upper tip, connected with the umbilicus by the median umbilical ligament, is called the apex. The region between the openings of the two ureters and the urethra is the trigone. The wall of the bladder has three major layers. The mucous membrane lining is transitional epithelium. The middle layer is three sheets (longitudinal, circular, longitudinal) of smooth muscle, called the detrusor muscle. The outer layer on the superior surface is the visceral peritoneum; on the lateral and inferior surfaces it is areolar connective tissue.
The bladder is supported by numerous ligaments; it is supplied with blood by the superior, middle, and inferior vesical arteries, and drained by numerous veins and lymphatics; and it is innervated by branches of the third and fourth sacral nerves by way of the hypogastric plexus.
PHYSIOLOGY: The bladder has a normal storage capacity of 500 ml (about 16 oz) or more. An average of 40 to 50 oz (about 1.2 to 1.5 L) of urine is excreted in a 24-hr period, but this varies with the amount of fluid ingested and the amount lost through exhalation, sweat, and the bowels. Inability to empty the bladder is known as retention and may require catheterization. Sphincter muscles are part of the mechanism that controls retention within the bladder.