The major organs of the urinary system are the urethra, the bladder, two kidneys and two ureters. These organs work together to rid the body of waste, which is excreted in the form of urine.
The kidneys are located in the middle of the back, one on each side of the spinal column. A kidney is roughly the size of a fist, and it contains filters that remove waste from the blood. The kidneys regulate the amount of water within the body. The kidneys also help regulate blood pressure, produce vitamin D and secrete erythropoietin, a hormone that helps in the formation of new red blood cells.
Each kidney is connected to the urinary bladder by a small, tube-like structure, or ureter. If these tubes become infected, a person is diagnosed with a urinary tract infection.
Consisting of smooth muscles, the bladder's main function is to store urine. When functioning normally, the bladder holds approximately 500 milliliters of urine. The main bladder muscle is the detrusor muscle. When the bladder receives a signal that it is full, the detrusor muscle relaxes and releases the urine.
The urine leaves the bladder and flows through the urethra to exit the body. In men, the urethra measures approximately 6 to 8 inches, but in women, the urethra is approximately 1.5 inches long. This shortened length possibly contributes to women's higher propensity to develop urinary tract infections.