Functions of arteries, veins and capillaries.

• ARTERIES

STRUCTURE:

Relatively thick wall

Smooth muscle

Elastic fibres

Lined with smooth layer of endothelial cells and narrow lumen

FUNCTIONAL SIGNIFICANCE:

• Withstannds high blood pressure
• Alters diameter of lumen to vary blood flow
• Allow walls to stretch when blood is pumped into the artery and then recoil, smoothing blood flow
• Low friction

CAPILLARIES

STRUCTURE

Very thin wall (just one cell thick)

FUNCTIONAL SIGNIFICANCE

• Allows rapid exchange between blood and tissues

VEINS

STRUCTURE

Relatively thin wall

Very little smooth muscle/elastic fibres

Wide lumen

Valves- to prevent back flow

FUNCTIONAL SIGNIFICANCE

• Blood under low pressure
• No pulse of blood so no stretching and recoiling
• Large volume acts as blood reservoir
• Stop backflow (valves)