Renin is an enzyme secreted by the kidneys that plays a critical role in the regulation of blood pressure and fluid balance. It initiates the renin-angiotensin-aldosterone system (RAAS) cascade by converting angiotensinogen into angiotensin I.
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Renin release is stimulated by low blood pressure, low sodium content in the kidney filtrate, or sympathetic nervous system activation.
Renin converts angiotensinogen, a protein produced by the liver, into angiotensin I.
Angiotensin I is further converted to angiotensin II by the enzyme angiotensin-converting enzyme (ACE), primarily in the lungs.
Angiotensin II causes vasoconstriction and stimulates aldosterone release from the adrenal glands, both of which increase blood pressure.
Renin secretion is regulated through a feedback mechanism involving blood pressure, blood volume, and sodium concentration.