Renin-angiotensin-aldosterone system

Question 1

Renin-angiotensin-aldosterone system?

Answer 1

Adrenal cortex (mnemonic GFR - ACD):

• zona Glomerulosa (on outside): mineralocorticoids, mainly Aldosterone

zona Fasciculata (middle): glucocorticoids, mainly Cortisol

zona Reticularis (on inside): androgens, mainly Dehydroepiandrosterone (DHEA)

Question 2

Renin?

Answer 2

• an enzyme that is released by the renal juxtaglomerular cells in response to reduced renal perfusion
• other factors that stimulate renin secretion include hyponatraemia, sympathetic nerve stimulation
• hydrolyses angiotensinogen to form angiotensin I

Question 3

Angiotensin II?

Answer 3

• angiotensin-converting enzyme (ACE) in the lungs converts angiotensin I → angiotensin II
• angiotensin II has a wide variety of actions:
• causes vasoconstriction of vascular smooth muscle leading to raised blood pressure and vasoconstriction of efferent arteriole of the glomerulus → increased filtration fraction (FF) to preserve GFR. Remember that FF = GFR / renal plasma flow
• stimulates thirst (via the hypothalamus)
• stimulates aldosterone and ADH release
• increases proximal tubule Na+/H+ activity

Question 4

Aldosterone?

Answer 4

• released by the zona glomerulosa in response to raised angiotensin II, potassium, and ACTH levels
• causes retention of Na+ in exchange for K+/H+ in distal tubule

Question 5

Answer 5