Physiological Functions of the Kidney
Excretion of waste products of metabolism and unwanted foreign materials: The major metabolic waste products include urea, creatinine, bilirubin, uric acid and metabolites of protein, nucleic acid, haemoglobin and various hormones.
Kidneys also aid in eliminating pesticides, drugs and food additives that enter by different means to the body.Maintenance of water and electrolyte balances: The kidneys can alter either the rates of absorption or excretion or the rates of both water and ions like sodium, potassium, chloride, calcium, hydrogen, magnesium and phosphate to regulate the fluid and electrolyte balance in the body.
Regulation of arterial pressure: Arterial pressure is maintained on a long-term basis by adjusting the kidneys’ excretion of sodium and water. Angiotensin II, a vasoactive peptide, has a vital role in the short-term maintenance of blood pressure produced in the body with the help of renal proteolytic enzyme renin.
Acid-base regulation: Kidneys can regulate excess hydrogen ions and acids, like sulphuric and phosphoric acids, to maintain the pH of body fluids.
Erythropoietin production: In hypoxic conditions, kidneys can produce hormone-like erythropoietin (EPO), which stimulates erythrocyte production.
Calcium homeostasis by calcitriol formation: The kidneys can produce the metabolically active derivative of vitamin D-1,25, dihydroxy cholecalciferol (calcitriol or vitamin D3). It is essential in maintaining the normal calcium deposition in bones and reabsorption of calcium from the gastrointestinal tract.
Glucose synthesis: When the blood glucose level lowers, kidneys can synthesise glucose by gluconeogenesis.
9.3