There is a decrease in pressure as blood moves away from the heart.
Arteries have an outer layer of connective tissue containing elastic fibres, and a middle layer of 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.
The smooth muscle surrounding arteries can contract causing vasoconstriction and can relax causing vasodilation. This controls blood flow within the arteries.
Capillaries form dense networks around body tissues and have very thinwalls to allow efficient exchange of materials.
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.
