Category: endocrine_axis
Major blood-pressure + volume homeostasis loop. Renin (from JG cells) cleaves liver-derived angiotensinogen to angiotensin I (decapeptide, inactive). ACE (pulmonary endothelium) cleaves AT-I to angiotensin II (octapeptide, potent vasoconstrictor + aldosterone secretagogue). AT-II → AT1 receptor (vasculature, adrenal cortex) → systemic vasoconstriction + aldosterone release. Aldosterone acts on the distal tubule + collecting duct via MR to increase Na+/H2O reabsorption + K+/H+ excretion. ACEi block ACE; ARBs block AT1; MRAs (spironolactone, eplerenone) block aldosterone receptor; direct renin inhibitors (aliskiren) block the first step.