Home > For Consumers > How do the kidneys work?
  • We are sorry, but NCBI web applications do not support your browser and may not function properly. More information

PubMed Health. A service of the National Library of Medicine, National Institutes of Health.

Informed Health Online [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-.

Informed Health Online.

How do the kidneys work?

Last Update: April 28, 2011.

A healthy person has two kidneys, which look like oversized beans. The kidneys are located to the right and left of the spine, just below your ribcage.

Your kidney is about as big as a bar of soap or the size of your fist. It weighs between 135 and 150 grams. The indented edge of the kidney is turned inward towards the spine. At the middle of this indentation a tube called the ureter leaves the kidney, and nerves, and blood and lymph vessels also lead in and out of the kidney. Each kidney is covered by three layers made out of fat or connective tissue, the so-called kidney capsule (or renal capsule). These layers give the kidney extra stability, protect it from external harm and anchor it in the surrounding tissue.

The kidney is surrounded by a thin outer renal cortex. There are about 2.4 million renal corpuscles in the renal cortex. These make urine. The renal medulla is found inside the kidney. Blood vessels and winding renal tubules run through the renal medulla. Urine passes through these renal tubules, then through the renal pelvis to the ureter, and then on to the urinary bladder.

Grafik: Längsschnitt Niere

The kidneys are our body’s sewage treatment plants: They produce urine, which makes it possible to get rid of waste products or toxins that arise in the body or that we have consumed in food and drinks. Examples of these are ammonia and urea, which are made when proteins are broken down. The body is also able to get rid of medicine, drugs or toxins though urine.

Besides producing urine, the kidneys have many other important functions. They regulate the body’s water balance by either holding back water or releasing it with the urine. When the kidneys hold back water, more liquid enters the blood vessels. The volume of blood increases, and the blood pressure rises. When the kidneys release water, the volume of blood decreases and the blood pressure falls. There are also special cells in the kidneys that produce the protein renin. This enzyme causes blood pressure to rise as well.

The kidneys keep the pH value of the blood as constant as possible too, to make sure that it does not get too acidic or too basic. They also produce two important hormones: calcitriol and erythropoietin. Calcitriol is the active form of vitamin D and regulates the amount of calcium in the body, as well as performing other functions. Erythropoietin promotes the production of red blood cells. If there is too little sugar (glucose) in the blood, the kidney can make it from the amino acid calledglutamine and release it into the bloodstream.

Author: German Institute for Quality and Efficiency in Health Care (IQWiG)

© IQWiG (Institute for Quality and Efficiency in Health Care)

PubMed Health Blog...

read all...

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...