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Function of the Kidney

The primary function of the kidney is to continuously remove nitrogenous wastes (mainly urea) from the body.  This, however, is not its only function.  It performs a number of other crucial functions, making it one of the most versatile organs of the body. 


In this article, we outline eight (8) key functions performed by the kidneys.

1. Primary Function: Removing Wastes Products from the Blood

Filtering blood is the primary function of the kidney.  This process is handled by the urinary excretory system, of which the kidneys are the main organs. Every day the kidneys process about 200 quarts (190 liters) of blood and filters out about 2 quarts of waste products and extra water. 

Waste is any substance that is not useful to the body. This could be any substance or chemical that the body cannot use at all, or even if the body can use it, if it is present in excess of what the body needs then the excess is classified as waste. If wastes are allowed to accumulate in the body, the results can be deadly. It is, therefore, crucial for wastes to be eliminated from the body, relatively quickly.

2. Urine Formation - Another Vital Function of the Kidney

Once the kidneys have filtered the blood and removed the waste products from it, the next step is to get rid of the wastes from the body. Urine formation is the process by which the kidneys prepare waste products, filtered from the blood, for elimination from the body.

The kidneys produce and eliminate urine by a sophisticated and somewhat complex process. During the filtering process, the kidneys determine the correct volume of water and the correct amount of chemicals (such as sodium, phosphorous and potassium) that should remain in the blood.


3. Regulating the body's water volume

The body is made up primarily of water. In fact, our body-weight is made up of approximately 50-60% water. Water is absolutely essential for many of the body's biological functions, but having too much or too little of it can cause serious problems. Excessive water in the body can dilute the blood, negatively affecting the environment in which the cells operate. On the other hand, insufficient water can cause circulatory shock and neurological dysfunction.

Thankfully, the Kidneys are specially equipped to regulate and maintain the correct volume of water in the body.  

4. The Kidneys Regulate The Body's Salt Content

Salt and water are regulated by the kidneys through a similar process. If you had a salty meal, for example, the salt is absorbed into your blood. When the salty blood reaches the kidneys the excess salt is removed and passed into the urine.

The relative amount of water and salt in the blood give the blood a particular concentration, which is necessary for good health. By regulating the amount of salt and water in the blood, the kidneys ensure that the concentration and volume of the blood stay at the correct level at all times.

5. Regulating Blood Pressure

The kidneys regulate blood-pressure by hormonal reactions.  Renin (REE-nin) is an enzyme secreted by the kidneys, which helps to control blood pressure and regulate electrolyte balance. If, for instance, blood-pressure begins to fall, the kidneys release the enzyme renin. This enzyme converts blood protein into a hormone called angiotensin.

Angiotensin then induces the adrenal gland to release another hormone called aldosterone. This hormone causes sodium and water to be reabsorbed into the blood, thereby increasing blood-volume and blood-pressure. The response of the kidneys to aldosterone helps to regulate the level of salt in the blood.

6. Production of Hormones is Another Function of The Kidney

Some important hormones are produced in the kidneys. One such hormone is erythropoietin (eh-RITH-ro-POY-eh-tin). It plays a key role in the production of red blood cells in the bone marrow.

When the kidneys detect a decline in the red blood cells in the body, it produces erythropoietin. This hormone is released into the bloodstream and goes to the bone marrow, which triggers the production and release of more red blood cells.

Bar Chart

7. Regulating pH Balance

Regulating the body's pH balance is another important function of the kidney. If the blood is too acidic, meaning that there is an excess of hydrogen ions, the kidneys remove these excess ions into the urine.

Bacteria (which cause many serious degenerative diseases) flourish in an acidic environment. The kidneys help to maintain the blood plasma at a neutral pH 7.4. By regulating the body's pH, the kidneys help to maintain an environment that prevents diseases and promotes the efficient functioning of all bio-systems within the body.

8. Processing Vitamin D

Not many people are aware that processing vitamin D is a function of the kidney. Here's what the kidneys do to help process vitamin D:  The kidneys convert calcidiol to calcitriol, which is an active form of vitamin D. In this active form, vitamin D promotes calcium absorption by the small intestine and makes it available for bone development.

Other Related Pages


BLOOD - Why must it always be filtered by the kidneys?

Blood has many functions.  It is responsible for transporting cells, oxygen and nutrients around the body...

kidney function tests

Kidney Function Tests

"Creatinine clearance test" and "urine protein test" are among the various tests conducted to evaluate the kidneys.

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