## **Core Concept**
The Glomerular Filtration Rate (GFR) is a critical indicator of kidney function, reflecting the rate at which fluid filtered by the glomeruli is passed into the Bowman's capsule. Preservation of GFR is essential for maintaining renal function and overall health. Various renal alterations can affect the GFR, including changes in glomerular capillary hydrostatic pressure, oncotic pressure, and the permeability of the glomerular filtration barrier.

## **Why the Correct Answer is Right**
The correct answer, , implies a condition where there is a proportional increase in both the afferent and efferent arteriolar resistance. This balanced increase in resistance maintains the glomerular hydrostatic pressure relatively constant, thus preserving the GFR. When both afferent and efferent arterioles constrict to a similar degree, the balance between the forces favoring filtration (hydrostatic pressure) and those opposing it (oncotic pressure) remains relatively stable. This balance ensures that the GFR is maintained.

## **Why Each Wrong Option is Incorrect**
- **Option A:** would decrease the GFR. This scenario typically decreases the hydrostatic pressure within the glomerulus, reducing the driving force for filtration and consequently lowering the GFR.
- **Option B:** could potentially increase the GFR in the short term by increasing the glomerular capillary hydrostatic pressure. However, it does not preserve the GFR in a balanced or sustainable manner and can lead to glomerular damage over time.
- **Option D:** would likely decrease the GFR. This condition increases the oncotic pressure within the glomerular capillaries, which opposes filtration and decreases the GFR.

## **Clinical Pearl / High-Yield Fact**
A key concept to remember is that the kidneys have an autoregulatory mechanism that maintains a relatively constant GFR over a wide range of blood pressures (approximately 80-180 mmHg). This autoregulation involves adjustments in the resistance of the afferent and efferent arterioles to keep the glomerular hydrostatic pressure stable. Understanding this helps in predicting how different renal alterations will affect the GFR.

## **Correct Answer: C.**