The kidneys secrete a variety of hormones, including erythropoietin and the enzyme 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.

The kidneys produce the hormone renin, which is involved in blood pressure control. Production of the hormone is boosted when specialized muscle cells in the kidney's filtering units (the nephrons) detect a fall in the pressure of blood entering the kidney. The kidneys also produce the hormone erythropoietin, which stimulates the production of red blood cells in bone marrow. Lack of erythropoietin – caused by kidney failure, for example – leads to anemia; while overproduction – perhaps as a result of kidney cancer – can cause too many red blood cells to be produced. A synthetic version of the hormone is now used to help to prevent anemia in people with renal failure.

MORE INFO