How do kidneys adjust to changes in blood pressure?

Kidneys adjust to changes in blood pressure through the Renin-Angiotensin-Aldosterone System (RAAS).

The kidneys play a crucial role in maintaining blood pressure homeostasis. They do this through a complex system known as the Renin-Angiotensin-Aldosterone System (RAAS). This system is activated when the kidneys detect a drop in blood pressure or a decrease in sodium concentration in the blood.

When blood pressure falls, the kidneys respond by releasing an enzyme called renin. Renin acts on a protein in the blood called angiotensinogen, converting it into angiotensin I. This is then converted into angiotensin II by an enzyme called angiotensin-converting enzyme (ACE), which is found in the lungs. Angiotensin II is a potent vasoconstrictor, meaning it narrows the blood vessels, thereby increasing blood pressure.

Angiotensin II also stimulates the adrenal glands to release a hormone called aldosterone. Aldosterone acts on the cells of the kidney's tubules and prompts them to reabsorb more sodium and water back into the blood. This increases the volume of fluid in the body, which in turn raises blood pressure.

On the other hand, if blood pressure is too high, the kidneys can excrete more sodium and water, reducing the volume of fluid in the body and thus lowering blood pressure. This is achieved through a process called diuresis.

In addition to these mechanisms, the kidneys also produce a hormone called atrial natriuretic peptide (ANP) when blood pressure is high. ANP promotes the excretion of sodium and water, further helping to lower blood pressure.

In summary, the kidneys have a multifaceted role in blood pressure regulation, primarily through the RAAS, but also through diuresis and the production of ANP. These mechanisms allow the kidneys to respond to changes in blood pressure and maintain homeostasis.