Renin-Angiotensin-Aldosterone System Pathway

Angiotensin II Pathway

• Angiotensin II is produced through the Chymase pathway, which involves the precursor Angiotensinogen (453 a.a.).
• Angiotensinogen is converted to Angiotensin II by the enzyme Renin (10 a.a.).
• Angiotensin II acts on the kidney through the AT1 receptor.

Effects of Angiotensin II

• Angiotensin II causes vasoconstriction, leading to increased blood pressure.
• Angiotensin II stimulates aldosterone production in the adrenal cortex, leading to increased water reabsorption in the collecting duct.
• Increased water reabsorption results in increased extracellular fluid (ECF) volume.
• Angiotensin II also increases Na+/H2O uptake and K+ excretion in the kidneys.

ACE Inhibitors and ARBs

• ACE inhibitors, such as Enalapril and Captopril, block the conversion of Angiotensin I to Angiotensin II, leading to decreased blood pressure.
• ACE inhibitors can cause coughing as a side effect due to the accumulation of bradykinin.
• ARBs, such as Losartan and Valsartan, block the action of Angiotensin II on the AT1 receptor.
• Direct renin inhibitors, such as Aliskiren, block the production of Angiotensin II by inhibiting the action of Renin.
• Aldosterone antagonists, such as Eplerenone, block the action of aldosterone on the kidneys.

Renin and Angiotensinogen

• Renin is produced by the kidneys in response to decreased blood pressure.
• Angiotensinogen is produced by the liver and released into the bloodstream.
• Renin converts Angiotensinogen to Angiotensin I, which is then converted to Angiotensin II.

True or False Quiz Answers

• True: Angiotensin II stimulates ADH secretion in the adrenal cortex to cause increased water reabsorption in the collecting duct.
• True: Renin secretion from the kidney occurs in response to decreased blood pressure.
• False: Activation of AT1 receptors elicits vasodilation.
• False: The kidney releases angiotensinogen into the blood.
• False: Aldosterone is produced in the kidney.
• True: Angiotensin II stimulates aldosterone in the adrenal cortex to cause increased water reabsorption in the collecting duct.
• True: Renin secretion from the kidney occurs in response to decreased blood pressure.
• True: ACE is expressed in the liver.
• False: Kidney releases angiotensinogen into the blood.
• False: Aldosterone is produced in the kidney.