**Core Concept**
Constriction of efferent arterioles in the kidneys plays a crucial role in regulating blood pressure and maintaining renal function. The efferent arteriole is a small blood vessel that carries blood away from the glomerulus, where filtration of the blood occurs.

**Why the Correct Answer is Right**
Constriction of the efferent arteriole increases the resistance to blood flow out of the glomerulus, which in turn increases the hydrostatic pressure within the glomerulus. This increase in pressure facilitates the filtration of more fluid and proteins from the blood into the Bowman's capsule. As a result, the glomerular filtration rate (GFR) increases. The increase in GFR is mediated by the renin-angiotensin-aldosterone system (RAAS), which is activated in response to decreased blood volume or pressure.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because constriction of the efferent arteriole does not decrease the glomerular filtration rate (GFR). In fact, it increases GFR by increasing the hydrostatic pressure within the glomerulus.
* **Option B:** This option is incorrect because constriction of the afferent arteriole, not the efferent arteriole, would decrease the GFR. Constriction of the afferent arteriole increases the resistance to blood flow into the glomerulus, which decreases the hydrostatic pressure within the glomerulus and subsequently decreases GFR.
* **Option C:** This option is incorrect because constriction of the efferent arteriole does not decrease the blood pressure in the afferent arteriole. In fact, constriction of the efferent arteriole increases the blood pressure in the afferent arteriole by increasing the resistance to blood flow out of the glomerulus.

**Clinical Pearl / High-Yield Fact**
In patients with hypertension, constriction of the efferent arteriole can lead to increased GFR, which can exacerbate kidney damage. This is because the increased GFR can lead to increased filtration of proteins and other substances that can damage the kidney cells.

**Correct Answer: B. Decrease in GFR is caused by constriction of the afferent arteriole, not the efferent arteriole.**