Question

Describe briefly the effects of aldosterone on principal cell and intercalated cells (Type A and type B).

Answer 1

Aldosterone is a mineralcorticoid hromone produced by zona glomerulosa in the adrenal gland. Its primary function is to regulate sodium and potassium homeostasis in kidneys. It is responsible for sodium absorption and potassium excretion in the late distal tube and collecting duct in the nephrons in the kidney.

Aldosterone upregulates the expression of sodium channels and basolateral Na+/K+-ATPase pumps.  Na+/K+ -ATPase pumps actively transport three sodium ions out of the cell and two potassium ions in the cell thereby creating a concentration gradient which allows for passive diffusion of sodium into the cells alongwith water (sodium and water reabsoprtion) and secretion of potassium ions into urine.

In addition to maintaining sodium and potassium homeostasis, aldosterone also regulates the acid-base balance in the nephrons. In acid secreting type A intercalated cells, aldosterone regulates the secretion of H+ via H+/ATPase pumps resulting in secretion of protons into urine. And in type B intercalated cells, aldosterone activates the expression of pendrin which is an anion-exchanger, espcially chloride-bicarbonate exchanger, which in turn stimulates reabsoprtion of chloride ions and the secretion of bicarbonate ions into urine