1. Glomerular Filtration Rate: Watch the following video to understand how autor

Question

1. Glomerular Filtration Rate:

Watch the following video to understand how autoregulation can maintain a constant glomerular filtration rate (GFR) as mean arterial pressure (MAP) changes.

https://www.youtube.com/watch?v=CMZ2AormwgU

MAP changes over the course of the day depending upon activity levels. Changes in MAP lead to changes in GFR, which can negatively affect filtrate processing and urine production. Therefore, it is important to have autoregulatory mechanisms to maintain a constant GFR despite changes in MAP. Assuming that an ideal MAP would be about 100 mm Hg, explain how autoregulatory mechanisms could be used to maintain a constant GFR for each of the following MAPs:

a. 85
b. 130

Explanation / Answer

a. This is a condition where the MAP is lower than normal so the autoregulation system would try to increase the pressure by vasoconstriction of the renal arterioles to maintain the GFR. The juxtaglomerular cells of the arterioles are stimulated to release more renin, which stimulates the renin–angiotensin system, producing angiotensin I which is converted by Angio-Tensin Converting Enzyme (ACE) to angiotensin II. Angiotensin II then causes preferential constriction of the efferent arteriole of the glomerulus and increases the GFR.

b.This is a condition where the MAP is higher than normal so the autoregulation system would try to decrease the pressure by vasoconstriction of the afferent arterioles ( to decrease the blood flow) and vasodilation of the efferent arteriole to maintain the GFR. In a mechanism called tubuloglomerular feedback, the kidney changes its own blood flow in response to changes in sodium concentration. The sodium chloride levels in the urinary filtrate are sensed by the macula densa cells at the end of the ascending limb. When sodium levels are moderately increased, the macula densa releases ATP and reduces prostaglandin E2 release to the juxtaglomerular cells nearby. The juxtaglomerular cells in the afferent arteriole constrict, and juxtaglomerular cells in both the afferent and efferent arteriole decrease their renin secretion. These actions function to lower GFR. Further increase in sodium concentration leads to the release of nitric oxide, a vasodilating substance, to prevent excessive vasoconstriction.

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