The kidneys are located on either side of the spine just beneath the ribs. Each kidney is about the size of a fist. The kidneys filter the blood, maintaining an environment within the body which allows all the other organs to function properly.
Blood is brought to the kidneys from the heart through large blood vessels called arteries. As the blood passes through the kidneys, small functioning units within the kidneys filter out waste, excess salt, minerals and fluid. The clean blood returns to the heart through blood vessels called veins.
The waste and fluid collected by the kidneys is eliminated as urine. Urine flows from the kidney to the bladder through a tube called the ureter. Once the bladder is full an urge to urinate is sensed and a muscle at the neck of the bladder relaxes. This allows urine to flow out of the body through the urethra.
The second major function of the kidney is hormone production. These hormones help control the blood pressure, stimulate the bone marrow to produce red blood cells, and absorb calcium from food in order to strengthen bone.