Renin-angiotensin-aldosterone system physiology

At a glance

• RAAS defends effective circulating volume and blood pressure over minutes to days. It acts through vasoconstriction, renal sodium retention and thirst.
• Renin is the rate-limiting step. It cleaves angiotensinogen (from the liver) to angiotensin I; ACE, mostly on pulmonary endothelium, converts this to angiotensin II; angiotensin II stimulates aldosterone from the zona glomerulosa.
• Angiotensin II constricts the efferent arteriole to maintain GFR when perfusion falls. That one fact explains the creatinine rise with ACE inhibitors and ARBs in the volume-deplete; NSAIDs add to it by removing prostaglandin-mediated afferent dilation.