Question

What happened to the glomerular capillary pressure and GFR when you decreased the afferent radius? Increased it? Why do you suppose this occurred?

Answer 1

By definition , Glomerular filtration rate (GFR) is defined as the total quantity of filtrate formed in all the nephrons of both the kidneys in the given unit of time. Normal GFR is 125 mL/minute or about 180 L/day.

By definition, Glomerular capillary pressure is the pressure exerted by the blood in glomerular capillaries. It is about 60 mm Hg and, varies between 45 and 70 mm Hg. This pressure favors glomerular filtration.

Glomerular filtration rate is directly proportional to glomerular capillary pressure.

When glomerular capillary pressure increases, the GFR also increases. Capillary pressure, in turn depends upon the renal blood flow and arterial blood pressure.

When the afferent arteriole radius is decreased i.e Constriction of afferent arteriole occurs ; it reduces the blood flow to the glomerular capillaries, which in turn reduces GFR.

Since the blood flow to the glomerular capillaries decreases, pressure of blood and capillary pressure also decreases. Thus Glomerular capillary pressure decreases .Also since amount of renal blood flow decreases, filtration rate decreases .Thus GFR is also decreased.