Renin Angiotensin System: responds by speed and intensity of vasoconstriction

2021-05-26 03:49 PM

Renin is a protein enzyme released by the kidneys when arterial blood pressure falls too low. In turn, it increases arterial blood pressure in several ways, thereby helping to correct the drop in blood pressure.

In addition to the kidney's ability to control blood pressure through changes in extracellular fluid volume, the kidney also has a powerful mechanism for blood pressure control: the renin-angiotensin system.

Renin is a protein enzyme released by the kidneys when arterial blood pressure falls too low. In turn, it increases arterial blood pressure in several ways, thereby helping to correct the drop in blood pressure.

The figure shows an experiment demonstrating the effect of bleeding on arterial blood pressure under two conditions: (1) with the renin-angiotensin system active and (2) functionally inactive (the system was disrupted by a renin-blocking antibody). Note that after bleeding, enough to cause an acute fall in arterial blood pressure to 50 mm Hg, blood pressure rises again to 83 mm Hg when the renin-angiotensin system is functional. In contrast, it increased to only 60 mm Hg when the renin-angiotensin system was blocked. This phenomenon suggests that the renin-angiotensin system is strong enough to return blood pressure to more than half of normal within minutes of major bleeding. So, it can sometimes be used to save life, especially in circulatory shock.

Figure. Compensatory effects of the renin-angiotensin vasoconstrictor system after major bleeding.

Note also that the renin-angiotensin vasoconstrictor system requires about 20 minutes to fully function. Therefore, it is slightly slower in blood pressure control than in the nervous reflexes and sympathetic norepinephrine-epinephrine system.