It refers to the elimination/removal of metabolic wastes from the body. There are four major organs of excretions : kidney, lungs, skin and the liver. Out of these four organs kidneys are the primary excretory organs that eliminate metabolic waste products in the form of urine. The major functions of urine are:
- Excretions of wastes and toxins such as urea, uric acid, ammonia and excess salts.
- Maintenance of water balance and electrolyte balance in the body
- Regulation of blood pressure by producing angiotensin, a substance that constricts blood vessels and signals the body to retain water and sodium when blood pressure is low.
- Regulating the acid base balance to keep the blood pH 7.2-7.4 and body healthy.
- Regulation of RBC development in bone marrow with the secretion of harmone erthyropoietin.