Blood Vessels & their functions

Arteries carry blood away from the heart,

arterioles control blood flow from arteries to capillaries,

capillaries link arterioles to veins,

veins carry blood back to the heart,

structures:

Tough outer layer- resists pressure changes,   muscle layer-contracts and controls blood flow,   elastic layer-helps to maintain blood pressure by stretching and springing back,   thin inner endothelium-smooth toprevent friction and thin to allow diffusion.

• Thick muscle layer- smaller arteries can be constricted and dilated to control the volume of blood passing through them
• Thick elastic layer- to keep the blood pressure high-stretching and recoiling helps to maintain high pressures
• Thick wall-resist the vessel bursting under pressure
• No valves- blood is under high pressure therefore does not flow backwards.

• Thick muscle- contraction of muscle allows constriction of lumen which restricts the flow of blood
• Thin elastic layer- blood pressure is lower

• Thin muscle layer- veins carry blood away from tissues so their constriction and dilation cannot control the flow of blood to the tissues
• Thin elastic layer- low pressure within veins does not cause them to burst, pressure too low to create recoil action
• Thickness of wall is small- pressure within veins is low to create risk of bursting, allows them to be flattened easily aiding the flow of blood
• valves- ensure blood doesnt flow backwards

• Walls consist of only the lining layer- makes them thin-short diffusion distance-allows rapid diffusion of material between blood and cells
• Numerous & highly branched- providing large SA
• Narrow lumen- brings them closer to the cells to which they supply oxygen- reduces diffusion distance
• Spaces between endothelial cells- allow white blood cells to escape to deal with infections