Your kidneys are bean-shaped organs, each about the size of your fist. They are located near the middle of your back, just below the rib cage, one on each side of the spine. The kidneys are sophisticated trash collectors. Every day, your kidneys process about 200 quarts of blood to sift out about 2 quarts of waste products and extra water. The wastes and extra water become urine, which flows to your bladder through tubes called ureters. Your bladder stores urine until you go to the bathroom.
The wastes in your blood come from the normal breakdown of active muscle and from the food you eat. Your body uses the food for energy and self-repairs. After your body has taken what it needs from the food, wastes are sent to the blood. If your kidneys did not remove these wastes, they would build up in the blood and damage your body. In addition to removing wastes, your kidneys help control blood pressure. They also help make red blood cells and keep your bones strong.
A kidney stone is a solid piece of material that forms in a kidney out of substances in the urine. A stone may stay in the kidney or break loose and travel down the urinary tract. A small stone may pass all the way out of the body without causing too much pain. A larger stone may get stuck in a ureter, the bladder, or the urethra. A problem stone can block the flow of urine and cause great pain.