Bodily Defenses Image Map

Cell operations of the kidney

The first place that blood from the stomach and intestines goes is to the liver. But then the blood leaving the liver goes to the heart and is pumped directly to the kidneys. Kidneys regulate the balance of water and salts in the body, but they also have a very important role in detoxication. 

With about 200 quarts being pumped through the kidneys every day, they do a big job for such a small organ! The main job is to take all of the blood in the body and clean it. This means:

  • filtering blood to hold back the cells   

  • reabsorbing much of the filtered water and certain chemicals

  • actively secreting certain chemicals that do not get eliminated by the filtering

What happens in the kidney?

Each kidney contains about one million microscopic units, called GLOMERULI, which work together to clean the blood.

GF = glomerulus filtering. TR = tubular reabsorption. TS = tubular secretion.

So, you see that blood is filtered, giving up much of the water and dissolved substances it contains. Then, much of the water and some of the dissolved substances are reabsorbed into blood. Finally, some dissolved substances in blood are actually secreted into the urine.

See Animations of Kidney Function

Filtered, No Reabsorption.  Blood chemicals are filtered into urine. 

Filtered, Partial Reabsorption.  Some of the filtered blood chemicals are partially re-absorbed into blood.

Filtered, and Secreted.  Blood chemicals are not only filtered, but also actively secreted into the urine.

Summary of Chemical Changes of Filtered Blood

Reabsorbed sugar, sodium, vitamins, nutrients, water
Secreted hydrogen ion, potassium, ammonia, drugs, toxins


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