What Are the Functions of the Kidneys?

By filtering the blood, the kidneys are essential for maintaining the body´s fluid balance and chemical environment. In addition, the kidneys also produce several hormones.

The main functions of the kidneys are:1

  • Washing out wastes via the urine. Wastes are produced in the body, for example, during protein breakdown. Examples of wastes are urea, uric acid and creatinine. If these substances accumulate in the body, they can reach toxic concentrations (“uraemia”) and cause damage to many different organs.
  • Regulation of water, sodium, hydrogen ions, and other electrolytes (i.e., potassium, phosphate, calcium). By modifying the composition of the urine, the kidneys maintain not only the volume of the body’s fluids but also their composition. These mechanisms adjust according to the body’s needs and the intake of water and electrolytes.
  • Hormone syntheses and breakdown. The kidneys are the exclusive site for the production of active vitamin D (calcitriol), which acts on the intestine to increase calcium uptake, and on the bones to maintain normal mineralization. Furthermore the kidneys produce erythropoietin (spoken: eh-RITH-ro-POY-eh-tin), and renin (spoken: REE-nin). The growth factor erythropoietin stimulates the bone marrow to produce red blood cells. Renin helps to regulate blood pressure. The kidneys also degrade certain hormones, such as parathyroid hormone, calcitonin, and insulin.


  1. Tortora G, Derrickson B: Principles of Anatomy and Physiology, 11th Edition. Wiley 2006.
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