The arteries carry blood from the heart while veins return blood to it. With both, their structure is related to their function.
Blood in the arteries is under high pressure generated by the heart. The arteries have:
The blood in veins is under lower pressure than the blood in arteries. The veins have:
Unlike arteries, veins have one-way valves in them to keep the blood moving in the correct direction.
The function of capillaries is to allow food and oxygen to diffuse to cells while waste is diffused from cells. Capillaries have thin walls - only one cell thick - that allow them to effectively perform their function.
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