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Heart disease

Arteries and veins

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:

  • thick outer walls
  • thick layers of muscle and elastic fibres.


The blood in veins is under lower pressure than the blood in arteries. The veins have:

  • thin walls
  • thin layers of muscle and elastic fibres.

Unlike arteries, veins have one-way valves in them to keep the blood moving in the correct direction.

Cross-section of a vein


Capillary cross-section

Capillary cross-section shows thin walls

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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