Final answer:
Renin, the proteolytic enzyme produced by juxtaglomerular cells, initiates the renin-angiotensin-aldosterone system by converting angiotensinogen to angiotensin I, leading to increased blood pressure and fluid balance.
Step-by-step explanation:
The proteolytic enzyme synthesized by the juxtaglomerular cells of the kidney is renin. Renin is released in response to decreased blood pressure or increased sympathetic nervous activity. It catalyzes the conversion of the plasma protein angiotensinogen, which is made by the liver, into angiotensin I. Renin is integral to the renin-angiotensin-aldosterone system, a hormonal cascade pathway that helps regulate blood pressure and fluid balance in the body. When blood pressure is low, renin is secreted by the granular cells of the afferent arteriole within the juxtaglomerular complex. Once released, renin acts on angiotensinogen to produce angiotensin I, which is further converted to angiotensin II in the lungs by the angiotensin-converting enzyme (ACE). Angiotensin II then functions as a potent vasoconstrictor, increasing blood pressure, and stimulates the release of aldosterone from the adrenal cortex, which promotes sodium and water retention, further aiding in blood pressure regulation.