What is the effect of constriction of efferent aeriole and dilatation of afferent aeriole on glomerular filtration rate?
**Core Concept**
The regulation of glomerular filtration rate (GFR) involves complex interactions between the afferent and efferent arterioles, which are critical in maintaining renal blood flow and glomerular pressure. The myogenic response of the arterioles and tubuloglomerular feedback mechanisms play significant roles in modulating GFR.
**Why the Correct Answer is Right**
Constriction of the efferent arteriole increases resistance against the blood flowing out of the glomerulus, which in turn increases the glomerular hydrostatic pressure. This increase in hydrostatic pressure enhances the filtration of fluid through the glomerular capillaries, thereby increasing the GFR. Simultaneously, dilatation of the afferent arteriole decreases resistance against blood entering the glomerulus, which also contributes to an increase in glomerular hydrostatic pressure and subsequently GFR. The combined effect of these changes results in an increase in glomerular filtration rate.
**Why Each Wrong Option is Incorrect**
**Option A:** This option would imply a decrease in GFR, but constriction of the efferent arteriole and dilatation of the afferent arteriole have the opposite effect.
**Option B:** This option would suggest that constriction of the efferent arteriole and dilatation of the afferent arteriole have no effect on GFR, which is incorrect as these changes can significantly modulate glomerular hydrostatic pressure and GFR.
**Clinical Pearl / High-Yield Fact**
In the context of renal physiology, the regulation of GFR is a critical mechanism for maintaining proper kidney function. Understanding the effects of vasoconstriction and vasodilation on the afferent and efferent arterioles is essential for appreciating the pathophysiology of renal diseases, such as hypertension and kidney failure.
**Correct Answer:** C.