Blood vessels

What are the 3 main blood vessels

• Arteries

• Veins

• Capillaries

Describe the arteries

• Maintains high pressure by elastic tissue which stretches/recoils.

• It has a small lumen and smooth muscle which contracts and relaxes to widen or constrict lumen.

• Has thick walls which contain collagen

• Endothelium is folded, unfolds when artery stretches

Describes the veins

• Blood flows at low pressure to heart due to thinner layers of collagen, smooth muscle and elastic tissue

• Has a large lumen

• Have valves to prevent backflow

• Found in skeletal muscle contraction of muscle moves blood along

Describe the capillaries

• Very narrow lumen 7 micrometres wide which is the diameter of one RBC

• Narrow lumen increases time for exchange by diffusion

• Leaky walls to allow plasma and dissolved substances to leave blood

• Walls are one cell thick

What are the tissues found in blood vessels

• Elastic fibres

• Collagen

• Smooth muscle

Describe role and structure of elastic fibres

• Made of elastin and gives stretch and flexibility to blood vessels

• Can stretch when force applied and recoil when force removed

Describe role and structure of collagen

• It is a strong structural protein, made up of strong fibres

• Give support to maintain the shape and volume of blood vessels

• Found in tendons, cartilage, ligaments and skin

Describes the role and structure of smooth muscle

Contracts and relaxes to change lumen size

What are arterioles

• Link arteries and capillaries

• Have more smooth muscle in their walls than arteries this means that:

They can constrict/ dilate to divert blood to individual organs. Vasoconstriction prevents blood flowing into a capillary bed. Vasodilation allows blood back into capillary

• Less elastin as pulse is weak

What is the capillary beds

• Network of capillaries running through tissue

• Contain precapillary sphincters which help regulate flow of blood to tissues ( A bit like valves open and close to regulate blood flow)

What are venules

• Link capillaries to veins

• Combine to form veins

• Collect blood from capillary bed and carry towards veins

• Thin walls, small amount of smooth muscle, elastin and collagen

Describe how valves in veins work

Prevent backflow of blood as blood moves forward when muscles nearby contract, when muscles relax pressure drops so valves close.