How do kidneys regulate blood pressure?

The kidneys play a crucial role in regulating blood pressure primarily through their ability to control fluid balance and vascular resistance. They achieve this through two main mechanisms: the regulation of blood volume and the secretion of various hormones.

When the kidneys sense changes in blood pressure, they adjust the volume of blood (by either conserving water or increasing urine output) to help maintain homeostasis. For example, if blood pressure is low, the kidneys can retain water, leading to an increase in blood volume, which, in turn, raises blood pressure. This is largely mediated through the renin-angiotensin-aldosterone system (RAAS), which is stimulated when blood pressure falls, leading to vasoconstriction and increased blood pressure.

Additionally, the kidneys regulate the resistance of blood vessels. Through the release of hormones like angiotensin II, they can cause vasoconstriction of peripheral blood vessels, enhancing vascular resistance and contributing to an increase in blood pressure as well.

Thus, the combination of managing fluid levels and regulating blood vessel constriction exemplifies how the kidneys effectively maintain blood pressure within a desired range.