Bladder

Bladder, muscular sac in the lower abdomen of all mammals that stores urine produced by the kidneys. Urine is carried to the bladder through 2 tubes called ureters and is emptied through the urethra by the contraction of a sphincter muscle. The term is also used to designate any similar organ in plants or animals; for example, the swim bladder in fish and the vesicles in some seaweeds.

See also: Kidney; Urine.