Renin-Angiotensin-Aldosterone System
? ACEI and pregnancy
? Mechanism of action
? Monitoring of ACEI
? Hypokalemia/hyperkalemia as result of RAAS
2. Hypertension
? Classification of primary and secondary & etiology
? DEEPICT secondary HTN
? Symptoms, labs, when to admit?
? Treatments ? Beta-blockers, Ca2+ channel blockers, diuretics
? Refractory HTN
? Atherosclerosis and HTN
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Review of Case
? Silver wiring
? Creatinine clearance
? Calculation & what it means
? Explain CHF ? relation to OTC medications (NSAIDs)
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Renin-Angiotensin System
? Renin is serine acid protease protein enzyme released by kidneys when arterial pressure falls too low
? Renin synthesized and stored in inactive form (prorenin) in juxtaglomerular cells (JG cells) of kidneys
? JG cells are modified smooth muscle cells in walls of afferent arterioles immediately proximal to glomeruli
? Decreased arterial pressure ? intrinsic reactions in kidneys cause many prorenin molecules in JG cells to split and release renin
? Most renin enters renal blood and passes out of kidneys into circulation
? Small amts of renin remain in local fluids of kidney and initiate intrareneal functions
? Renin acts enzymatically on another plasma protein called angiotensinogen to release 10-aa peptide, angiotensin I
? Angiotensin I has mild vasoconstrictor properties but not enough to cause significant changes in circulatory function
? w/in few seconds to minutes after formation of angiotensin I, 2 more aa's are split off from angiotensin I to form 8-aa peptide, angiotensin II
? conversion to AII occurs in lungs while blood flows through small vessels of lungs, catalyzed by angiotensin converting enzyme that is present in endothelium of lung vessels
? AII is powerful vasoconstrictor, but only persists in blood for 1-2 mins b/c it's rapidly inactivated by multiple blood and tissue enzymes collectively called angiotensinases
? Angiotensin II has 2 main effects that can elevated arterial pressure
1) vasoconstriction in many areas of body occurs rapidly ? acute effect
? arterial vasoconstriction > venous vasoconstriction
? arteriole constriction increases total peripheral resistance ? raises arterial pressure
? mild venous constriction promotes increased venous return of blood to heart ? helps heart pump against increasing pressure
2) decreased excretion of both salt and water by kidneys ? long-term effect
? causes increase in extracellular fluid volume ? increased arterial pressure during subsequent hours and days
? renin-angiotensin vasoconstrictor system requires 20 min to become fully active
? thus: slower to act for pressure control than nervous reflexes and sympathetic norepinephrine-epinephrine system
? angiotensin II causes kidneys to retain both salt and water in 2 major ways:
1) AII acts directly on kidneys to cause salt and water retention
? Mechanisms of AII on kidneys:
? Constrict renal arterioles ? diminishes blood flow through kidneys ? less fluid filters through glomeruli into tubules
? Slows flow of blood through kidney ? reduces pressure in peritubular capillaries ? causes rapid reabsorption of fluid from tubules
? Direct effect on tubular cells ? increase tubular reabsorption of sodium and water
2) AII causes adrenal glands to secrete aldosterone ? aldosterone increases salt and water reabsorption by kidney tubules
? Activation of renin-angiotensin system causes rate of aldosterone secretion to also increase
? Function of aldosterone ? increase sodium reabsorption by kidney tubules ? increases total body extracellular fluid sodium ? increased Na causes water retention ? increases extracellular fluid volume ? long-term elevation of arterial pressure
? Direct effect of angiotensin on kidneys is perhaps 3 or more times as potent as indirect effect acting through aldosterone
Role of Renin-Angiotensin system in maintaining normal arterial pressure despite salt intake
? Increased salt intake ? elevated extracellular fluid volume ? elevated arterial pressure ? increased blood flow through kidneys ? reduced rate of secretion of renin ? decreased renal retention of salt and water ? return of extracellular fluid volume almost to normal ? return of arterial pressure almost to normal
? Thus: renin-angiotensin system is automatic feedback mech... displayed 300 characters
