Hormone functions of the kidney

Question 1

Hormonal functions of the kidney - general + Vitamin D

Answer 1

• There are 2 main endocrine roles of the kidney: (i) activation of vitamin D (calcitriol), which is important in Ca2+ homeostasis + ii) erythropoietin to stimulate red blood cell production
• Vitamin D from the diet, or from skin synthesis (produced from cholesterol in skin when exposed to UV light), is biologically inactive. - It is activated by 2 enzymes, the first in the liver + the second in the PT of the nephron
• converted into 1,25-dihydroxy vitamin D (calcitriol).
• Many varied roles that calcitriol plays in body, including increasing muscle mass & muscle strength, regulating hair cycle, + even a possible role in reducing symptoms of respiratory infectious diseases such as COVID
• The main actions of calcitriol are to maintain Ca2+ and PO4- levels in the blood & maintain skeletal calcium balance by promoting Ca2+absorption in the intestines.
• Vitamin D deficiency can result in lower bone mineral density.

Question 2

Hormonal functions of the kidney - erythropoietin

Answer 2

• Erythropoietin (EPO) is a hormone that controls red blood cell production in the bone marrow.
• It is produced in the endothelial cells of peritubular capillaries in cortical nephrons.
• Under hypoxic conditions, the kidney will produce + secrete EPO to increase the production of red blood cells
• EPO levels in blood are usually low, but in response to hypoxia EPO production may increase 1000-fold.
• Clinically EPO is used to treat anaemia associated w/ chronic renal failure & cancer + possibly other causes
• If EPO levels are too high & too many red blood cells are produced it cause increase the viscosity of the blood = can lead to problems w/ blood flow + risks of clotting