Sacs formed of muscular and ﬁbrous tissue and lined by a mucous membrane, which is united loosely to the muscular coat so as freely to allow increase and decrease in the contained cavity. Bladders are designed to contain some secretion or excretion, and communicate with the exterior by a narrow opening through which their contents can be discharged. In humans there are two: the gall-bladder and the urinary bladder.
Gall-bladder This is situated under the liver in the upper part of the abdomen, and its function is to store the BILE, which it discharges into the intestine by the BILE DUCT. For further details, see LIVER.
Urinary bladder This is situated in the pelvis, in front of the last part of the bowel. In the full state, the bladder rises up into the abdomen and holds about 570 ml (a pint) of urine. Two ﬁne tubes, called the ureters, lead into the bladder, one from each kidney; and the urethra, a tube as wide as a lead pencil when distended, leads from it to the exterior – a distance of 4 cm (1••• inches) in the female and 20 cm (8 inches) in the male. The exit from the bladder to the urethra is kept closed by a muscular ring which is relaxed every time urine is passed.