Question

Glomerular filtration pressure is normally

• A. 15-20 mm Hg
• B. 25-30 mm Hg
• C. 35-50 mm Hg
• D. 65-80 mm Hg

Answer 1

The correct option is B 25-30 mm Hg

Effective filtration pressure (EFP) refers to the net driving forces for water and solute transport across the glomerular membrane. EFP is a function of three variables
1) Glomerular Hydrostatic Pressure - It is blood pressure in a glomerular capillaries due to narrower efferent arteriole and is the chief determinant of EFR. Its value is 75 mmHg.
2) Capsular Hydrostatic Pressure - the hydrostatic pressure driving fluid into the Bowman's capsule. Its value is 20 mmHg.
3) Blood Colloid Osmotic Pressure - It is osmotic pressure created in the blood of glomerular capillaries due to plasma proteins. Its value is 30 mmHg.
Using these variables, the EFP is expressed as:

EFP = $P_{cap}-(CO{P}_{cap}+P_{Bow})$

= 75 - (30 + 20) = 25 mm Hg.