Renin - Angiotensin - Aldosterone System

Renin - Angiotensin - Aldosterone System

1. Juxtaglomerular cells secrete renin

   • 3 factors are involved in activating renin secretion:
     • 1.) PERFUSION PRESSURE - a decrease in perfusion pressure causes renin secretion
       • 2.) SYMPATHETIC NERVE ACTIVITY - increased activity of SNS that innervates afferent arterioles increases renin secretion
         • 3.) DELIVERY OF NaCl TO THE MACULA DENSA - a decrease in NaCl to the macula densa activates renin secretion

2. Activated when ECF volume decreases and causes an increase in Na reabsorption

   • Increasing Na in ECF draws in water by osmosis to return ECF volume to normal
   • Indirectly causes reabsorption of Cl aswell as it is drawn across tight junctions by Em

3. Renin cleaves angiotensin ( a liver derived protein) to produce angiotensin I which is further cleaved by the converting enzyme ACE in the lungs to angiotensin II

   • Angiotensin II stimulates AT1 receptors to cause secretion of aldosterone from adrenal cortex
     • Aldosterone stimulates the NaK ATPase in the basolateral membrane and the Na channel in the apical membrane of principal cells in the collecting duct
   • Angiotensin II stimluates activity and insertion of NaH antiporter in proximal tubule cells to up-regulate Na reabsorption