The kidneys are a pair of internal organs that are each the size of a fist.
They are composed of several different types of tissues including blood vessels, tubules,and supporting structures. The purpose of the large blood vessels is to carry blood to and from the kidney.
Smaller blood vessels, called capillaries, filter the blood of water, salts, toxins, and medications. Once the blood is filtered, kidney tubules can reabsorb or secrete water, salts, or other substances based upon the needs of our body.
On a very hot day, we can reabsorb much of the filtered water and salt to prevent dehydration.
If we overeat and drink at a holiday party, our kidneys can eliminate extra water and salt to prevent us from becoming overloaded.
Fluid and salt in the urine are carried by a collecting system resembling a funnel to tubes called the ureters. The ureters carry the urine to the bladder where it can be stored until a convenient time for us to urinate.