What do the Kidneys do in The Body and What are Their Functions?

Human Kidney. Credit: AlonzoDesign

What do the kidneys do in the body? What are their functions? How can you know if your kidneys are doing their job? Check out the short answer and longer answers below.


Our bodies have two kidneys that are located on either side of the spine in our lower back. They are bean shaped and about the size of a fist.

Function - The Simple Answer

The primary function of the kidneys is to filter waste products from our blood.

Our kidneys filter between 120 and 150 quarts of blood each day, resulting in 1 to 2 quarts of urine. The urine travels down tubes called the ureters and is stored in the bladder until it is excreted (urination).

The Kidneys Under the Microscope

Within the kidneys are a million small units called nephrons that do the work of the kidneys. On one end of these tiny units there is something called the glomerulus where blood to be filtered enters the unit, and at the other end is a tubule. Surrounding the nephrons are capillaries arising from larger arteries which deliver blood to the nephrons. Plasma, but not blood cells or large proteins pass from the capillaries to the glomerulus and then back to the capillaries from the tubule.

Functions of the Kidney

The kidneys have several very important functions for the body, making the kidneys essential for life. If the kidneys fail, the body cannot function, and either dialysis or a kidney transplant are needed to restore its functions.

  • Prevent the Build up of Waste Products – The kidneys function as an intricate filter, removing normal waste products of metabolism, as well as toxins from the body. In the process of removing toxins, the kidneys may be damaged by these substances.
  • Regulate Fluid – Through holding on to fluids when a person is dehydrated, or eliminating excess fluids, the kidneys control fluid balance in the body.
  • Regulate Electrolytes – The kidneys play an important function in electrolyte balance in the body, regulating the levels of sodium, potassium, and phosphate. This maintaining of optimal levels of electrolytes is referred to as homeostasis - or equilibrium.
  • Regulate Blood Pressure – Through the production of a hormone called renin, the kidneys play an important role in regulating blood pressure. Learn more about the renin-angiotensin system.
  • Regulate Production of Red Blood Cells – The kidneys produce a hormone called erythropoietin which controls the production of red blood cells in the bone marrow.
  • Bone Health - The kidneys produce an active form of vitamin D which keeps the bones healthy.

Lab Analysis

Several blood and urine tests may be recommended to evaluate the kidneys. Some of these include:


National Kidney Foundation. How Your Kidneys Work. https://www.kidney.org/kidneydisease/howkidneyswrk

National Institute of Diabetes and Digestive and Kidney Diseases. The Kidneys and How They Work. 05/2014. http://asthma.about.com/od/treatmentoptions/a/Theophylline.htm