What hormone is released by the kidneys when blood pressure falls?

When blood pressure falls, the kidneys respond by releasing renin, an enzyme crucial in the regulation of blood pressure. Renin is produced by the juxtaglomerular cells of the kidneys in response to decreased renal perfusion pressure, which can occur due to various factors such as dehydration, blood loss, or volume depletion.

Renin initiates a cascade of events known as the renin-angiotensin-aldosterone system (RAAS). It catalyzes the conversion of angiotensinogen, produced by the liver, into angiotensin I. This inactive form is then converted into angiotensin II by the action of angiotensin-converting enzyme (ACE) primarily in the lungs. Angiotensin II has multiple effects, including vasoconstriction of blood vessels and stimulating the adrenal glands to release aldosterone. Aldosterone then acts on the kidneys to increase sodium and water reabsorption, ultimately raising blood volume and blood pressure.

In contrast, the other hormones listed have different roles unrelated to the initial response of the kidneys to low blood pressure. Aldosterone acts later in the RAAS pathway after renin is released. ADH (antidiuretic hormone, also known as vasopressin) is involved in