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Capillary Hydrostatic Pressure

Introduction to capillary hydrostatic pressure

Capillary hydrostatic pressure: is the force that is exerted by a fluid against the capillary wall. It helps in the movement of fluid between capillaries and the interstitial fluid. Highest capillary hydrostatic pressure is observed at the arteriolar end of the capillary and lowest pressure is observed at the venular end. Capillary hydrostatic pressure created due to the pumping action of heart.

Role of capillary hydrostatic pressure in movement of fluid between capillaries and the interstitial fluid:

The net filtration pressure is the pressure which determines the movement of fluid between capillaries and interstitial fluid. It is the difference between the capillary hydrostatic pressure and the osmotic pressure.

If the capillary hydrostatic pressure is greater than osmotic pressure then fluid will leave the capillary and if the capillary hydrostatic pressure is less than that of osmotic pressure fluid will enter into the capillary.

Capillary hydrostatic pressure > Osmotic pressure ----- fluid leave the capillary

Capillary hydrostatic pressure < Osmotic pressure ----- fluid enters the capillary

At the arterial end of a capillary the blood pressure on the average is about 32 mm, which is higher than the pressure of the tissue fluid outside the capillaries, this helps to force water out of the capillaries.

At arterial end of the capillary:

Capillary hydrostatic pressure = 30 mmHg

Osmotic Pressure = 25 mmHg

Fluid moves into the capillary with net filtration pressure 5 mmHg

Due to the increased cross-sectional area and frictional resistance of the capillaries, the pressure decreases to about 15 mm Hg at the venous end of the capillary bed, which helps to draw water into the capillaries.

At venous end of the capillary:

Capillary hydrostatic pressure = 20 mmHg

Osmotic Pressure = 25 mmHg

Fluid moves out of the capillary with net filtration pressure -5 mmHg

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Capillary Hydrostatic Pressure Diagram

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capillary hydrostatic pressure

Fig1.capillary hydrostatic pressure


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