Your Kidneys and How They Work
What Do My Kidneys Do?
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. 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 waste 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 kidneys remove wastes and extra
water from the blood to form urine. Urine flows from the kidneys to the bladder
through the ureters.
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-repair. After your body has taken what it needs from
the food, waste is sent to the blood. If your kidneys did not remove these
wastes, the wastes would build up in the blood and damage your body.
The actual filtering occurs in tiny units
inside your kidneys called nephrons. Every kidney has about a million nephrons.
In the nephron, tiny blood vessels called capillaries intertwine with tiny
urine-carrying tubes called tubules. A complicated chemical exchange takes
place, as waste materials and water leave your blood and enter your urinary
At first, the tubules receive a combination
of waste materials and chemicals that your body can still use. Your kidneys
measure out chemicals like sodium, phosphorus, and potassium and release them
back to the blood to return to the body. In this way, your kidneys regulate the
body's level of these substances. The right balance is necessary for life, but
excess levels can be harmful.
In the nephron (left), tiny blood
vessels intertwine with urine-collecting tubes. Each kidney contains about 1
In addition to removing wastes, your
kidneys release three important hormones:
Erythropoietin (eh-RITH-ro-POYeh-tin), or
EPO, which stimulates the bones to make red blood cells.
Renin (REE-nin), which regulates blood
The active form of vitamin D, which helps
maintain calcium for bones and for normal chemical balance in the