Question

Effective filtration pressure in the glomerulus in the kidney of man is about:

• A. + 50 mm Hg
• B. + 75 mm Hg
• C. + 80 mm Hg
• D. 10 to 25 mm Hg

Answer 1

The correct option is D

10 to 25 mm Hg

The correct option is D.

Explanation of correct option:

1. Glomerular filtration is the first step in urine formation wherein the kidneys filter out the excess fluid and wastes out of the blood.
2. This process is dependent on three pressures as mentioned below:

• Glomerular blood hydrostatic pressure i.e. GBHP refers to the blood pressure as the blood enters the glomerulus. This pressure favors filtration and is approximately 60 mm Hg.
• Capsular hydrostatic pressure i.e. CHP opposes filtration as it represents the resistance of the capsule wall and the fluid present in the renal tubule. It is approximately 20 mm Hg.
• Blood colloidal osmotic pressure i.e. BCOP also opposes the filtration process and is generated due to the albumin and globulin proteins present in the glomerular capillaries because of which some water is taken back into the capillaries. It is approximately 30 mm Hg.

The effective filtration pressure is calculated by subtracting the forces that resist filtration from the GBHP. Hence, the calculation is as follows:

Step 1: Given data:

$$\begin{gathered} \mathrm{GBHP}=60\mathrm{mm}\mathrm{Hg} \\ \mathrm{CHP}=20\mathrm{mm}\mathrm{Hg} \\ \mathrm{BCOP}=30\mathrm{mm}\mathrm{Hg} \end{gathered}$$

Step 2: Applying the formula:

$\mathrm{Effective}\mathrm{filtration}\mathrm{pressure}=\mathrm{GBHP}-(\mathrm{CHP}+\mathrm{BCOP})$

Step 3: Solving the equation to get the required value:

$$\begin{gathered} \mathrm{Effective}\mathrm{filtration}\mathrm{pressure}=60-\left(20+30\right) \\ \mathrm{Effective}\mathrm{filtration}\mathrm{pressure}=60-50 \\ \mathrm{Effective}\mathrm{filtration}\mathrm{pressure}=10 \end{gathered}$$

Final answer: Effective filtration pressure in the glomerulus in the kidney of man is about 10 to 25 mm Hg