Renin-angiotensin-aldosterone (RAAS)
MCAT glossary · Biological & Biochemical Foundations of Living Systems
Definition
Low BP/Na⁺ → renin → angiotensin I → ACE → angiotensin II (vasoconstriction) → aldosterone (Na⁺ retention) → water retention.
Renin-angiotensin-aldosterone (RAAS) in plain English
RAAS is your body's emergency system for propping up blood pressure when it drops too low — for example after you lose blood or get dehydrated. When your kidneys sense low pressure or low sodium, they release an enzyme called renin, which kicks off a relay: it helps make angiotensin II, a molecule that squeezes your blood vessels tighter (narrower pipes = higher pressure) and triggers the hormone aldosterone. Aldosterone tells the kidneys to hold onto sodium (salt), and since water follows salt, your body retains more fluid — more fluid in the vessels also pushes pressure back up. It's basically a self-regulating thermostat for blood pressure, which is also why many blood-pressure medicines work by blocking a step in this chain.
Also called: RAAS
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Which hormonal profile would most likely be observed in their blood sample to maintain homeostasis?
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