BRAINCAKEHydrostatic Pressure
Hydrostatic pressure is the pressure a fluid exerts on the walls of its container. In the circulation, it is the pressure of the blood pushing against the walls of the vessels, and it is generated by the contraction of the heart's ventricles.
In a capillary, hydrostatic pressure pushes fluid out through the gaps between the endothelial cells. It therefore acts in the opposite direction to oncotic pressure, which draws water back in.
Hydrostatic pressure is not constant along a capillary. Blood enters from an arteriole, so pressure is highest at the arterial end. As blood moves along the narrow capillary, pressure falls, because of friction with the capillary wall and because fluid is lost from the blood.
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Key terms in this lesson
- oedema
- The build-up of excess fluid in the tissues, for example when too much tissue fluid is formed or too little is drained away.
More in Circulatory Systems
- Capillaries
- Veins and venules
- Tissue Fluid
- Oncotic Pressure
- Arterial End of Capillaries
- Venous End of Capillaries
- Formation of Lymph
- Lymph Nodes
All 33 lessons in Circulatory Systems · All Edexcel AS-level Biology topics