Kidney is an endocrine organ. Comment.

Kidney is an endocrine organ. It produces three important hormones: erythropoietin, calcitriol (1,25-dihydroxycholecalciferol) and renin. They also synthesize prostaglandins which affect many processes in kidney.

ERYTHROPOIETIN:

• It is a peptide hormone which regulates erythropoiesis.
• It is a glycoprotein containing 165 amino acids. Its receptors are present on the membrane of RBC precursors. Binding of the hormone reduces apoptosis of these cells-multiple cell survive and therefore complete their development into mature erythrocytes.
• In adults, approx. 90% of the erythropoietin is synthesized in the kidneys (interstitial cells) and remaining amount in liver.
• Erythropoietin is also abused as doping substance especially in endurance athletics.

CALCITRIOL:

(1,25-dihydroxycholecalciferol) Final activation of vitamin D to the active hormone calcitriol takes place in kidneys 1-hydroxylation of 25 hydroxycholecalciferol to 1,25-dihydroxycholecalciferol. Calcitriol stimulate the small intestine for protein synthesis allowing absorption of Ca2+ and phosphates. This ensures availability of Ca2+ and phosphate for bone growth.

RENIN:

Renin is a part of renin-angiotensin aldosterone (RAAS). In case of insufficient blood flow to the system, kidneys (decrease in blood volume). Cells of renal juxtaglomerular apparatus begin synthesis of protein renin. Renin is an enzyme which catalyzes the conversion of angiotensinogen to angiotensin I. Angiotensin I is then converted to angiotensin II by angiotensin converting enzyme which stimulates aldosterone synthesis and causes vasoconstriction.