The kidneys have four main roles in the body :

  Excretion of wastes
- The kidneys excrete a variety of waste products produced by            metabolism. These include the nitrogenous wastes urea, from        protein catabolism, and uric acid, from nucleic acid metabolism.

  Acid-base homeostasis
- Two organ systems, the kidneys and lungs, maintain acid-base homeostasis, which is the maintenance of pH around a relatively stable value. The kidneys contribute to acid-base homeostasis by regulating bicarbonate (HCO3-) concentration.

 Blood pressure regulation
-  Long-term regulation of blood pressure predominantly depends upon the kidney. This primarily occurs through maintenance of the extracellular fluid compartment, the size of which depends on the plasma sodium concentration. Although the kidney cannot directly sense blood pressure, changes in the delivery of sodium and chloride to the distal part of the nephron alter the kidney's  secretion of the enzyme renin.

 Hormone secretion
- The kidneys secrete a variety of hormones, including erythropoietin, calcitriol, and renin. Erythropoietin is released in response to hypoxia (low levels of oxygen at tissue level) in the renal circulation. It stimulates erythropoiesis (production of red blood cells) in the bone marrow. Calcitriol, the activated form of vitamin D, promotes intestinal absorption of calcium and the renal reabsorption of phosphate. Part of the renin- angiotensin-aldosterone system, renin  is an enzyme involved in the regulation of aldosterone  levels.