If the efferent arteriole constricts while the afferent arteriole remains unchanged, the glomerular filtration rate __________.

• A. increases
• B. does not change
• C. decreases
• D. cannot be determined

Answer: (A)

Verified step by step guidance

1. Understand the role of the afferent and efferent arterioles in the kidney. The afferent arteriole brings blood to the glomerulus, while the efferent arteriole carries blood away.
2. Recognize that the glomerular filtration rate (GFR) is influenced by the pressure within the glomerulus, which is affected by the diameter of these arterioles.
3. Consider the effect of constricting the efferent arteriole. Constriction increases resistance to blood flow out of the glomerulus, which can increase the pressure within the glomerulus.
4. Analyze how increased glomerular pressure affects GFR. Higher pressure in the glomerulus typically leads to an increase in the filtration rate, as more fluid is pushed through the filtration barrier.
5. Conclude that if the efferent arteriole constricts while the afferent arteriole remains unchanged, the glomerular filtration rate is likely to increase due to the increased pressure in the glomerulus.