Role of RAS in kidney

• The Renin-Angiotensin System (RAS) regulates blood pressure, fluid balance, and electrolyte homeostasis, with critical roles in kidney function and cardiovascular health.

Components of the RAS

1) Renin

• Released by the juxtaglomerular cells in response to low blood pressure, low blood volume, or low sodium.

2) Angiotensinogen

• A protein produced by the liver that is converted to angiotensin I by renin.

3) Angiotensin I

• Inactive, but converted into angiotensin II by angiotensin-converting enzyme (ACE).

4) Angiotensin II

• A potent vasoconstrictor that also stimulates aldosterone secretion from the adrenal cortex.

Role of RAS in Kidney Functions

1) Regulation of Blood Pressure and Volume

• Angiotensin II causes vasoconstriction, raising blood pressure, and stimulates aldosterone secretion to increase sodium and water reabsorption, raising blood volume.

2) Sodium and Water Reabsorption

• Aldosterone promotes sodium reabsorption in the distal tubules and collecting ducts, and water follows sodium, increasing blood volume.

3) Direct Action on the Kidneys

• Angiotensin II enhances sodium reabsorption in the proximal tubule and reduces renal blood flow by constricting arterioles.

4) Feedback Regulation

• High levels of angiotensin II inhibit further renin release. Natriuresis (excretion of sodium) helps balance sodium reabsorption and water retention, maintaining blood pressure.

Pathophysiological Implications

• Overactivation of RAS can lead to hypertension and chronic kidney disease, creating a cycle that worsens both kidney function and blood pressure regulation.