RAS Role 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 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 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.

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