Blood Vessels

Elastic fibres - can stretch and recoil providing vessel walls with flexibility.

Smooth muscle - contracts or relaxes able to change the size of the lumen.

Collagen - provides structural support to maintain the shape and volume of the vessel.

Carry blood away from the heart.

• carry oxygenated blood.
• walls contain elastic fibres, smooth muscle and collagen.
• arterioles have more smooth muscle and less elastin.

Link the arterioles and venules.

• small lumen.
• substances are exchanged through the capillary wall.
• provide a very large surface area for diffusion.
• total area of capillaries is larger so the rate of blood flow falls, giving more time for exchange.
• very thin wall, one endothelial cell thick.

Carry blood away from the heart.

• carry deoxygenated blood.
• no pulse.
• low blood pressure.
• one-way valves to prevent back flow.
• walls contain lots of collagen.
• wide lumen.
• smooth, thin lining.
• many of the bigger veins run between big,active muscles so when they contract they squeeze the vein, forcing blood twoards the heart.
• breathing movements of chest act as a pump.