Unit 2.5

Arteries have an outer layer of connective tissue containing elastic fibres and a middle layer containing smooth muscle with more elastic fibres. The elastic walls of the arteries stretch and recoil to accommodate the surge of blood after each contraction of the heart. Biggest

2nd smallest (Archie v Charlie) Veins have an outer layer of connective tissue containing elastic fibres but a much thinner muscular wall than arteries. They contain valves to prevent the backflow of blood.

Capillaries allow exchange of substances with tissues through their thin walls. Smallest

Archie vs Charlie it needs to withstand the pressure heart produces whereas vein are usually low pressure (from Lewis dms)