Final answer:
Renin activates the renin-angiotensin-aldosterone cascade, which increases blood pressure by converting angiotensinogen to angiotensin I and ultimately to angiotensin II that constricts blood vessels and stimulates aldosterone release, promoting sodium and water retention.
Step-by-step explanation:
Renin plays a crucial role in the regulation of blood pressure through its involvement in the renin-angiotensin-aldosterone system (RAAS). Specifically, renin activates the renin-angiotensin-aldosterone cascade, leading to an increase in blood pressure. When blood pressure is low, cells in the juxtaglomerular apparatus of the kidneys release renin. Renin is an enzyme that converts angiotensinogen, produced by the liver, into angiotensin I. Angiotensin I is then converted to angiotensin II by the angiotensin converting enzyme (ACE). Angiotensin II acts as a powerful vasoconstrictor, narrowing blood vessels and thereby increasing pressure. Additionally, it stimulates the adrenal cortex to release aldosterone, which leads to increased sodium reabsorption and water retention in the kidneys, further elevating blood pressure.