Question

Normal interstitial fluid hydrostatic pressure is?

• A. 10 to 15 mmHg
• B. -5 to 0 mmHg
• C. 20 to 30 mmHg
• D. -10 to -20 mmHg

Hint:

Free interstitial fluid pressure is mildly subatmospheric, around -1 mmHg.

Answer 1

The Correct Option is B

Step 1: The interstitial fluid hydrostatic pressure is the pressure exerted by the free fluid in the tissue spaces. In most tissues it is slightly below atmospheric pressure, that is, it is mildly negative or subatmospheric.

Step 2: The accepted average value of normal interstitial fluid hydrostatic pressure is about \(-1\) mmHg, and across different tissues it commonly ranges from about \(-5\) mmHg up to roughly \(0\) mmHg. This makes option (b), -5 to 0 mmHg, the correct choice.

Step 3: The slightly negative pressure is maintained mainly by continuous lymphatic pumping, which removes excess fluid and free protein from the interstitium. This negative pressure helps hold tissues together and keeps the interstitial space relatively dry.

Step 4: Positive values such as 10 to 15 mmHg or 20 to 30 mmHg are wrong because such pressures would cause widespread tissue separation and oedema. A range of -10 to -20 mmHg is far too negative for free interstitial fluid pressure.