BRAINCAKEVenous End of Capillaries
As blood flows along a capillary, it loses fluid and meets resistance, so its hydrostatic pressure falls. The plasma proteins stay in the blood, so the oncotic pressure stays about the same (it even rises slightly, because the proteins become a little more concentrated as water leaves).
By the time blood reaches the venous end, the hydrostatic pressure is lower than the oncotic pressure. There is now a net inward pressure. Because the plasma has a lower water potential than the tissue fluid, water moves back into the capillary by osmosis.
net inward pressure = oncotic pressure − hydrostatic pressure
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Key terms in this lesson
- hydrostatic pressure
- The pressure a fluid exerts on the walls of its container; in a capillary it pushes fluid out through the gaps between the endothelial cells.
- oncotic pressure
- The pressure created by plasma proteins, which are too large to leave the capillaries, that draws water back into the capillaries by osmosis.
- 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
- Hydrostatic Pressure
- Arterial End of Capillaries
- Formation of Lymph
- Lymph Nodes
All 33 lessons in Circulatory Systems · All Edexcel AS-level Biology topics