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
What Is "Renal Function"?
Your health care team may talk about the
work your kidneys do as renal function. If you have two healthy kidneys, you
have 100 percent of your renal function. This is more renal function than you
really need. Some people are born with only one kidney, and these people are
able to lead normal, healthy lives. Many people donate a kidney for
transplantation to a family member or friend. Small declines in renal function
do not cause a problem. In fact, you can be healthy with 50 percent of your
renal function if it remains stable.
But many people with 50 percent of their
renal function have a kidney disease that will get worse. You will have some
serious health problems if you have less than 20 percent of your renal
function. If your renal function drops below 10 to 15 percent, you cannot live
long without some form of renal replacement therapy -- either dialysis or