Renin - Angiotensin - Aldosterone System

Juxtaglomerular cells secrete renin
1. 3 factors are involved in activating renin secretion:
  1. 1.) PERFUSION PRESSURE - a decrease in perfusion pressure causes renin secretion
    1. 2.) SYMPATHETIC NERVE ACTIVITY - increased activity of SNS that innervates afferent arterioles increases renin secretion
      1. 3.) DELIVERY OF NaCl TO THE MACULA DENSA - a decrease in NaCl to the macula densa activates renin secretion
Activated when ECF volume decreases and causes an increase in Na reabsorption
1. Increasing Na in ECF draws in water by osmosis to return ECF volume to normal
2. Indirectly causes reabsorption of Cl aswell as it is drawn across tight junctions by Em
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
1. Angiotensin II stimulates AT1 receptors to cause secretion of aldosterone from adrenal cortex
  1. Aldosterone stimulates the NaK ATPase in the basolateral membrane and the Na channel in the apical membrane of principal cells in the collecting duct
2. Angiotensin II stimluates activity and insertion of NaH antiporter in proximal tubule cells to up-regulate Na reabsorption

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