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A UTI is an infection of one or more parts of the urinary tract. The urinary tract consists of two kidneys, two ureters, a bladder, and a urethra. The kidneys are bean-shaped organs found in the lower back below the ribcage. They filter waste out of the blood and produce urine to carry the waste and excess water out of the body. The urine is carried through the ureters (tubes) from the kidneys to the bladder.
The bladder is a hollow muscular organ that stores urine for a short time period. The bladder stretches as urine accumulates and at a certain point it signals to the body that it needs to relieve the growing pressure. A muscular valve (sphincter) at the opening of the bladder is relaxed and the bladder contracts to send urine through the urethra (a tube linking the bladder to the external surface of a persons skin) and out of the body.
A UTI can be due to infection in any part of the urinary tract. The most common type is infection involving the bladder (also known as cystitis). If the infection then spreads to the kidneys it is called pyelonephritis.
Last Review Date: July 23, 2015