How do kidneys work?

Most people think of the kidneys as organs concerned only with getting rid of waste material, but they have the double function of keeping back what should not go out in water. The composition of the body is stable, and the kidney helps to keep it so. In each kidney there are about 1,300,000 nephron units into which the blood comes. Here water and the dissolved material to be excreted are picked out and the blood returned to the stream.

One of the most significant tasks of the kidney is to retain sodium or salt while sending out acid material. The kidneys have a vital task; when they are damaged or find it impossible to handle their duties the whole human being suffers, sometimes to the point of death.

Due to the intimate knowledge of the working of the kidney assembled by physiologists, doctors now make a much more accurate diagnosis of what is wrong with the kidney than was possible formerly. There are many highly technical tests which are used on special occasions, but in the majority of instances the doctor can diagnose kidney troubles from the history of the patient and the examination of the urine. First he makes sure there is no albumin or protein in the urine which cannot be accounted for by known conditions. He looks for blood cells which may be related to disease of the kidneys or other portions of the renal tract. If there are elements in the urine called “casts,” he relates these to the progress of the disease. There are functional tests which measure the capacity of the kidneys to do their work.

Urination should be free from pain; the urine should come easily and regularly. Failure to hold the urine is abnormal, as is also the necessity to get up to urinate at night.