Final answer:
The shrinkage of vessel B increases resistance, potentially decreasing glomerular blood flow, while an increase in hydrostatic pressure in compartment C could increase GFR. However, without knowing the magnitudes of these changes, the GFR would likely stay the same due to opposing effects.
Step-by-step explanation:
When vessel B shrinks, this signifies a decrease in vessel diameter, which will dramatically increase resistance to blood flow according to the principle that resistance is inversely proportional to the radius of the vessel raised to the fourth power. Consequently, if vessel B is related to the afferent arteriole supplying blood to the glomerulus, a shrinkage would lead to decreased glomerular blood flow. Meanwhile, an increase in hydrostatic pressure in compartment C, which may represent the glomerular capsule, would tend to increase the glomerular filtration rate (GFR). However, without knowing the relative magnitudes of these changes, we cannot determine the overall effect on GFR. Therefore, the answer is that GFR stays the same because these two changes have opposing effects and we are given no information on the magnitude of each effect.