Which hormone is released in response to a drop in blood pressure as part of the RAAS system?

In the context of the Renin-Angiotensin-Aldosterone System (RAAS), renin is an enzyme released by the juxtaglomerular cells of the kidneys in response to a drop in blood pressure. This release is crucial because renin initiates a cascade of events that ultimately helps to elevate blood pressure and restore homeostasis.

When blood pressure falls, renin acts on angiotensinogen, a protein produced by the liver, to convert it into angiotensin I. Angiotensin I is then converted into angiotensin II by an enzyme known as ACE (Angiotensin-Converting Enzyme), primarily in the lungs. Angiotensin II is a potent vasoconstrictor that helps increase blood pressure by narrowing blood vessels. It also stimulates the release of aldosterone from the adrenal cortex, leading to increased sodium and water reabsorption in the kidneys, further assisting in raising blood pressure.

Understanding the role of renin in this process is essential, as it is the key initiator of the RAAS response to low blood pressure, influencing multiple pathways to restore blood volume and pressure effectively.