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 regulates blood flow to capillaries

• Less elastin as pulse is weak

Note:

Blood pressure lowers from arteries to arterioles to prevent rupture of capillaries. Achieved as they have more smooth muscle and a smaller lumen so increases resistance

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.

How are arteries and arterioles suited for their functions

Arteries:

Have small lumen but smooth muscle can constrict or relax to change its shape. Thick walls contain lots of elastic tissue and smooth muscle. Allows them to withstand high pressure of blood from heart, and elastic recoil helps maintain blood pressure

Arterioles:

Have a narrower lumen and more smooth muscle within their walls, which increases resistance and causes blood pressure to fall before it reaches capillaries, preventing damage. Smooth muscle allows vasoconstriction and vasodilation controlling amount of blood to capillary beds