Unit 2 AQA Biology - Blood Vessels

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Blood vessels
Arteries: Carry blood away from the heart
Arterioles: Control blood flow from arteries to capillaries
Capillaries: Link arterioles to veins
Veins: Carry blood towards the heart
Structure of blood vessels:
Tough outer layer ­ resists pressure
Muscle layer ­ can contract and control the flow of blood
Elastic layer ­ can stretch and recoil to maintain blood pressure
Endothelium ­ smooth layer to prevent friction
Lumen ­ not a layer ­ a cavity
Arteries:

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Thick muscle layer ­ control the flow of blood
Thick elastic layer ­ smooth surges from the heart
No valves
Arterioles:
Thicker muscle layer than arteries
Thinner elastic layer than arteries
No valves
Veins:
Thin muscle layer
Thin elastic layer
Valves
Capillaries
No muscle
No elastic
No valves
Thin layer of cells only
How does this relate to its function?
Thin layer of cells ­ short diffusion distance.
Numerous and highly branched ­ large SA for diffusion.
Narrow diameter ­ keep all cells close by.…read more

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