Which hormone is primarily involved in the regulation of blood pressure?

Renin plays a crucial role in the regulation of blood pressure through the renin-angiotensin-aldosterone system (RAAS). When blood pressure falls, the kidneys release renin, an enzyme that converts angiotensinogen, a protein produced by the liver, into angiotensin I. This substance is then converted to angiotensin II by angiotensin-converting enzyme (ACE) primarily in the lungs. Angiotensin II has several important effects: it constricts blood vessels, increasing systemic vascular resistance and consequently raising blood pressure. Additionally, angiotensin II stimulates the secretion of aldosterone from the adrenal glands, which promotes sodium and water retention by the kidneys, further increasing blood volume and blood pressure.

In summary, renin initiates a cascade of events that directly lead to an increase in blood pressure, making it a key hormone in this regulatory process. Other hormones listed, such as insulin, glucagon, and cortisol, are primarily involved in metabolic regulation and do not directly influence blood pressure in the same manner as renin does within the context of the cardiovascular system.