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How Do Your Kidneys Work?

  • Your two kidneys are vital organs that perform many functions to keep your blood clean and chemically balanced. Understanding how your kidneys work can help you to keep them healthy.

  • The kidneys remove wastes and extra water from the blood to form urine. They 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 reprocessing machines. Every day, they 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 the urine until you empty it by using the restroom. 

  • The wastes in your blood come from the normal breakdown of active tissues and from the food your 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, a glomerulus (or tiny blood vessel), intertwines with a urine collecting tube called a tubule. A complicated chemical exchange takes place as waste materials and water leave your blood and enter your urinary system.

  • 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, our kidneys regulate the body's level of these substances. The right balance is necessary for life, but excess levels can be harmful.

In addition to removing wastes, your kidneys release three important hormones:

  1. Erythropoietin (eh-RITH-ro-POY-eh-tin), or EPO, which stimulates the bone marrow to make red blood cells.
  2. Renin (REE-nin), which regulates blood pressure.
  3. Active Vitamin D, which helps maintain calcium for bones and for normal chemical balance in the body.

What is renal function?

  • Your health care team may talk about the work your kidneys do as your "renal function". If you have two healthy kidneys, you have 100% of your renal function. This is more renal function that you really need. some people are born with only one kidney, and are able to lead normal, healthy lives. Many people donate a kidney for transplantation to a family member or friend and still lead normal healthy lives. Small declines in renal function may not cause a problem. Many people with reduced renal function only get worse. You will have serious health problems if you have less than 25% of your renal function. If your renal function drops below 10-15%, you cannot live long without some form of renal replacement therapy like dialysis or transplantation.

(Adapted from National Kidney and Urologic Diseases Information Clearinghouse).