Normally, a person has two kidneys. The rest of the urinary tract consists of two ureters (the tubes connecting each kidney to the bladder), the bladder (an expandable muscular sac that holds urine until it is released from the body), and the urethra (a tube attached to the bladder that leads to the outside of the body). Each kidney continuously produces urine, which then drains through the ureter into the bladder at a low pressure. From the bladder, urine drains through the urethra and exits the body through the penis in males and at the vulva (the area of the external female genital organs) in females. Usually, urine is free of bacteria and other infectious organisms.

Last full review/revision November 2012 by Navin Jaipaul, MD, MHS