Hydrostatic pressure is defined as which of the following?

• A. Pushing of fluid out of the blood vessels
• B. Pressure within the lungs
• C. Pressure in the venous system
• D. Pressure created by the heart's contractions

Answer: (A)

Hydrostatic pressure is the force exerted by a fluid due to gravity. In the circulatory system, this pressure tends to push fluid out of capillaries into the surrounding tissue, especially at the arterial end of the microcirculation. Describing hydrostatic pressure as the pushing of fluid out of the blood vessels matches that mechanism, which is why it’s the best fit. The other statements refer to different pressures: pressure within the lungs is intrapulmonary pressure, pressure in the venous system is venous pressure, and pressure created by the heart’s contractions is arterial blood pressure generated by cardiac output.