Functions of the Kidney

Functions of the Kidney

The main function of the kidney is the maintenance of the interior composition of the body. Due to continued digestion and utilisation of food in the body, construction and destruction of the various body tissues, waste products are generated daily.

  • Excretion of waste products

If allowed to collect in the body, the function of the body is affected. These waste products are thrown out from the body by liver and intestines, lungs, skin and kidneys.

Kidneys excrete urea, creatinine and similar products in a concentrated form in urine. The amount of excretion closely balances the amount of production of these materials.

  •  Water and salt balance

Kidneys maintain salt and water balance in the body. When healthy, a person may drink upto 10 liters of water or as low as ½ litre in a day. The kidneys increase and decrease urine appropriately to maintaine the total body water.

About 1 litre of blood flows through kidney. Of this about 180 litres of water, some salts and small particle are filtered daily in the kidney. Of this 180 litres, only 1 to 2 litre is finally excreted as urine. The rest is absorbed back to the blood from urinary tubules. Thus kidneys can dilute or concentrate urine.

The body water in humans depends to a large extent on salt content of the body. In case of reduced intake of salt , kidneys limit salt wastage in urine and similarly if intake is high , kidneys try to excrete extra salt.

Kidneys also excrete phosphate, ammonia products, urates and various drugs ingested by humans.

  • Acid balance

Urine is acidic in nature as it has to carry the daily acids produced from metabolism and activities of daily living, exercise etc. by excreting acid the pH of the body tissue and blood is maintained in a narrow range.

  • Haemoglobin production

Kidneys produce a hormone called erythropoietin or EPO in short. EPO stimulates bonemarrow to produces RBCs and hemoglobin. Lack of EPO production in the kidneys leads to anemia or decreased  hemoglobin.

  • Bone Health

Vitamin D produced from the ultraviolet radiation from sun or ingested in food is inactive. The liver and kidneys transform this inactive form to active form. Lack of activation leads to various bone abnormalities, fractures, bone pains and muscle weakness.

Structure of the Kidney

Structure of the Kidney

There are 2 kidneys in human body. Each weighs about  125 gms. These are located one on each side of the spine in abdomen. These are covered and protected in their upper part by ribs. These are bean shaped and beans are said to be kidney shaped.

Each kidney has about 1 million filtering units. These are called renal corpuscles and can be seen by microscope . The ball like portion where formation of urine begins by filtering from blood is called glomerulus. The filtered fluid gets modified while passing through tube like structures.

Kidneys are very rich in blood supply. It gets more blood per 100 gms of tissue than any other organ except heart.  About one fifth of the total blood pumped by heart goes to the kidneys.

After the urine is formed in the kidneys, it comes to the urinary bladder by two tubes called ureters. The urine can be stored in bladder till voided at will. Various valve like structures prevent urine from flowing backwards and leakage through the urethra , the final part connecting bladder to the outside.