The Starling forces governing fluid movement across the glomerular capillary differ from those at skeletal muscle capillaries primarily because:
- A Glomerular capillary hydraulic conductance is much higher, enabling high filtration despite similar pressure gradients
- B Glomerular filtration is driven by a uniquely high hydraulic pressure (~55 mmHg) with negligible interstitial oncotic pressure opposition ✓
- C Glomerular capillary oncotic pressure exceeds hydraulic pressure, driving reabsorption
- D The glomerular basement membrane lacks charge selectivity, relying entirely on size selectivity
Correct answer: B. Glomerular filtration is driven by a uniquely high hydraulic pressure (~55 mmHg) with negligible interstitial oncotic pressure opposition
Explanation
Glomerular filtration is driven predominantly by the uniquely high glomerular capillary hydrostatic pressure (~55 mmHg), opposed by Bowman's space hydraulic pressure (~15 mmHg) and plasma oncotic pressure (~30 mmHg), giving a net filtration pressure of ~10 mmHg. The glomerular filtration coefficient (Kf) is also far higher than in most capillaries due to the large surface area and high hydraulic conductance. The GBM bears strong negative charges (heparan sulfate) providing additional charge selectivity beyond size alone.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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