Originally Posted by Bliss
what is the advantage of renin secretion by JG cells in response to increased sympathetic tone (B1)?
It is clearly mentioned in FA that if there is increased sympathetic tone- HR,contractility and renin secretion also increases.So, as per this concept, renin secretion by JG cells should decrease to counteract the increased renin secreteion caused due to increased sympathetic tone, isn't it? But,it's not happening so. Can anyone give explanation for this.Thanks in advance.
B1 stimulation is just one of the triggers that increase renin. There are B1 receptors on JG cells that increase renin in response to sympathetics. Just like there are B1 receptors on nodal cells that function to increase heart rate in response to sympathetic stimulation. Nothing is decreased to counteract anything. B1 stimulation is a physiologic mechanism of renin secretion, just like decreased renal pressure and decreased sodium in macula densa.
The advantage of sympathetic stimulation increasing renin is that 1) angiotensin 2 will directly vasoconstrict and increase mean arterial pressure, 2) it will constrict efferent arterioles in the kidneys and decrease RPF and 3) it will increase the synthesis of aldosterone which will do its own magic and decrease sodium loss (and water loss). All those things to maintain blood pressure, plasma volume and adequate perfusion of vital organs.