Which combination of changes would increase the glomerular filtration rate (GFR) the most?

• A. Decreased afferent arteriole diameter and increased efferent arteriole diameter
• B. Increased afferent arteriole diameter and decreased efferent arteriole diameter
• C. Increased afferent arteriole diameter and increased efferent arteriole diameter
• D. Decreased afferent arteriole diameter and decreased efferent arteriole diameter

Answer: (B)

Verified step by step guidance

1. Understand the concept of glomerular filtration rate (GFR): GFR is the rate at which the kidneys filter blood through the glomeruli. It is influenced by hydrostatic pressure in the glomerular capillaries, which is determined by the diameters of the afferent and efferent arterioles.
2. Analyze the role of afferent arteriole diameter: Increasing the afferent arteriole diameter allows more blood to flow into the glomerulus, raising the hydrostatic pressure and increasing GFR. Conversely, decreasing the afferent arteriole diameter reduces blood flow and lowers GFR.
3. Analyze the role of efferent arteriole diameter: Decreasing the efferent arteriole diameter creates resistance to blood leaving the glomerulus, increasing hydrostatic pressure and raising GFR. Increasing the efferent arteriole diameter reduces resistance, lowering hydrostatic pressure and decreasing GFR.
4. Combine the effects: To maximize GFR, you would need to increase the afferent arteriole diameter (to allow more blood into the glomerulus) and decrease the efferent arteriole diameter (to create resistance and maintain high pressure within the glomerulus).
5. Evaluate the options provided: Based on the physiological principles, the combination of increased afferent arteriole diameter and decreased efferent arteriole diameter would result in the greatest increase in GFR.