Bladder

Urine is stored in the urinary bladder, an expandable, muscular sac, until it is excreted from the body. Accumulated urine will pass out of the bladder via the urethra, which in female pigs will fuse with the vagina. In human females, the urethra and vagina are two separate openings. While the muscles that control the contraction of the bladder are involuntary, the muscles which control the opening to urethra are voluntary (skeletal muscle), and thus enables a person to decides when he or she will urinate