BRAINCAKEVeins and venules
Venules collect blood from the capillary beds. They are small vessels with very thin walls containing little or no muscle. Venules join together to form veins, which carry blood back to the heart. Most veins carry deoxygenated blood; the pulmonary vein is the exception, carrying oxygenated blood from the lungs to the left atrium.
By the time blood reaches the veins it has passed through the arterioles and capillaries, so it is at low pressure and flows smoothly without pulses. The structure of veins reflects this:
Thin wall. Veins have the same three layers as arteries, but the middle layer has much less smooth muscle and elastic tissue. The blood pressure is low, so a thick, elastic wall is not needed.
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More in Circulatory Systems
- Blood Vessels
- Arteries
- Arterioles
- Capillaries
- Tissue Fluid
- Oncotic Pressure
- Hydrostatic Pressure
- Arterial End of Capillaries
All 33 lessons in Circulatory Systems · All Edexcel AS-level Biology topics