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Facts

Chronic Kidney Disease (CKD) affects 26 million Americans. Early detection can help to prevent progression of the disease – which ultimately can lead to kidney failure and death. However, early detection can be difficult because the signs and symptoms of kidney disease, and even acute kidney failure, are often overlooked.

When it comes to kidney disease or kidney cancer, any well-informed patient must understand how the kidneys work.

The following is a reprint of information compiled and created by the National Kidney and Urologic Diseases Information Clearinghouse, a service of the National Institute of Health.

What do the kidneys do?

The kidneys remove wastes and extra water from the blood to form urine. Urine flows from the kidneys to the bladder through the ureters.

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 reprocessing machines. 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 wastes in your blood come from the normal breakdown of active tissues and from the food you eat. Your body uses 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—which is a tiny blood vessel, or capillary—intertwines with a tiny 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, your kidneys regulate the body’s level of these substances. The right balance is necessary for life, but excess levels can be harmful.

The kidneys remove wastes and extra water from the blood to form urine. Urine flows from the kidneys to the bladder through the ureters.

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

  • Erythropoietin (eh-RITH-ro-POY-eh-tin), or EPO, which stimulates the bone marrow to make red blood cells
  • Renin (REE-nin), which regulates blood pressure
  • Calcitriol (kal-suh-TRY-ul), the active form of 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 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 may not cause a problem.

But many people with reduced renal function have a kidney disease that will get worse. You will have serious health problems if you have less than 25 percent of your renal function. If your renal function drops below 10 to 15 percent, you cannot live long without some form of continuous renal replacement therapy — either dialysis or transplantation.

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