One of a pair of organs located in the right and left side of the abdomen which clear "poisons" from the blood, regulate acid concentration and maintain water balance in the body by excreting urine. The kidneys are part of the urinary tract. The urine then passes through connecting tubes called "ureters" into the bladder. The bladder stores the urine until it is released during urination.

The kidneys remove waste products from the blood and produce urine. As blood flows through the kidneys, they filter waste products, chemicals, and unneeded water from the blood. Urine collects in the middle of each kidney, an area called the renal pelvis. Urine then drains from the kidney through a long tube, the ureter, to the bladder, where it is stored.

The kidneys also make substances that help control blood pressure and regulate the formation of red blood cells.