Which substance is secreted by the kidneys to help monitor blood pressure?

The kidneys play a crucial role in regulating blood pressure, and one of their key mechanisms involves the secretion of renin. Renin is an enzyme that is released from the juxtaglomerular cells in the kidneys in response to low blood pressure, low sodium concentration, or sympathetic nervous system stimulation.

Once released, renin acts on a protein called angiotensinogen, which is produced by the liver, to convert it into angiotensin I. Angiotensin I is subsequently converted into angiotensin II, primarily in the lungs. Angiotensin II has several effects: it causes blood vessels to constrict, increases the secretion of aldosterone from the adrenal glands (which promotes sodium and water reabsorption), and stimulates thirst. All these actions lead to a rise in blood pressure.

In contrast, substances like aldosterone, angiotensin, and cortisol have roles in the broader context of blood pressure and fluid balance but are not directly secreted by the kidneys specifically for monitoring blood pressure. Aldosterone is regulated by angiotensin II and affects blood pressure indirectly through sodium reabsorption. Angiotensin, while pivotal in the response to renin, is not directly secreted by the kidneys. Cortisol is a steroid hormone