Hormones of heart, kidney and gastro intestinal tract

Hormone secretion is not confined to the classic endocrine glands — several organs perform it as a secondary, partial function. In the heart, cardiac muscle cells (cardiocytes) on the atrial wall secrete a peptide hormone called atrial natriuretic factor (ANF): when blood pressure rises, ANF is released and dilates blood vessels, helping bring pressure back down.

In the kidney, three hormones are made. Renin, secreted by the juxtaglomerular cells (JGA), raises blood pressure indirectly by triggering the formation of angiotensin in the blood. Erythropoietin, also secreted by the JGA cells, stimulates erythropoiesis — the formation of red blood cells — in the bone marrow, and is the key hormonal driver behind the body's response to low oxygen. Calcitriol, secreted by the proximal tubules of the nephron, is the active form of vitamin D3; it promotes calcium and phosphorus absorption from the intestine and accelerates bone formation. …