Sat27November0445PM 7

One factor determining glomerular filtration rate (GFR) in a normal patient is the net filtration pressure acting across the capillary membrane in the renal corpuscle.

Which single factor is most likely to determine the net filtration pressure?

(Please select 1 option)

Bowman's capsule hydrostatic pressure Incorrect answer selected

Glomerular capillary oncotic pressure

Bowman's capsule oncotic pressure

Efferent glomerular capillary hydrostatic pressure

Afferent glomerular capillary hydrostatic pressure This is the correct answer

Explanation

The net filtration pressure (NFP) is influenced by the Starling forces acting across the glomerular capillary membrane.

The glomerular hydrostatic pressures are approximately 60 mmHg at the afferent (arteriole) end and approximately 58 mmHg at the efferent (arteriole) end. Unlike most other capillary beds, the efferent end does not drain directly into a venule. The high resistance and pressure within the network of capillaries within the glomerulus aids the process of ultra filtration.

The hydrostatic pressure acting in the opposite direction is that within the Bowman's capsule is in the order of 15 mmHg.

The glomerular capillary oncotic pressure is in the order of 21 mmHg afferent and 33 mmHg efferent end. The interstitial pressure in Bowman's space is negligible and is not factored in.

NFP (afferent end) is calculated 60-15-21=24 mmHg

NFP (efferent end) is calculated 58-15-33=10 mmHg.

Average NFP is thought to be 17 mmHg sufficient to produce 180L/day of glomerular filtrate.

GFR= K1 x NFP

Where K1 is the filtration coefficient dependent on membrane permeability and surface area available.

Answer Statistics

1

21%

2

4%

3

6%

4

23%

5

48%

Times answered: 251