5. Explain the relationship between the structure and function of arteries, capillaries and veins

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Arteries have a thick outer layer of longitudinal collagen and elastic fibers to avoid leaks. It also contains a thick wall to deal with the high pressures, as well as a narrow lumen to maintain these high pressures and thick layers of muscle fibers to help pump the blood after a hearth beat. Its function is to carry blood away from the heart to the body, under high pressure.

Veins are responsible for returning the blood to the heart, under low pressure. It is composed of a thin outer layer of longitudinal collagen and elastic fibers, since there is no risk or leaking and bursting. It also has a thin walls that allows the vein to be pressed by muscles, helping to move the blood. It contains thin layers of muscle fibers, since the blood does not flow in pulses, and the lumen is wide because of the slow-flowing blood.

The capillaries' walls are made of a single layer of thin cells so the distance for diffusion is small. It has a very narrow lumen so that the capillary can fit into small spaces and contains pores between the cells to allow some of the plasma to leak out and from tissue fluid.