Blood vessels

• What are the 3 layers found in both arteries and veins?

  -tunica intima

  -tunica media

  -tunica externa
• What is the tunica intima?

  -the innermost layer of arteries and veins

  -single layer of endothelium

  -it is a smooth lining to reduce friction for blood flow

  -some arteries have it supported by elastin-rich collagen
• What is the tunica media?

  -middle layer of arteries and veins

  -contains elastic fibres and smooth muscle

  -thicker in arteries than veins

  -a pulse is felt in arteries as the elastic fibres recoil and push blood through the vessel

  -contraction of the muscle regulates blood flow and maintains blood pressure
• What is the tunica externa?

  -outer layer of arteries and veins

  -contains collagen fibres which resist overstretching
• What are the functions of arteries?

  -carries blood away from the heart

  -thick, muscular walls withstand high blood pressure

  -arteries branch into smaller vessels called arterioles, that further divide into capillaries
• What are the functions of veins?

  -they have larger lumens and thinner walls with less muscle than arteries

  -blood pressure and flow rate are lower than arteries

  -semi-lunar valves prevent backflow

  -for veins above the heart, blood returns to the heart by gravity. It moves through other veins by the pressure from surrounding muscles
• What are the functions of capillaries?

  -form a vast network that penetrates all the tissues and organs of the body

  -blood from capillaries collects into venules, which take blood into veins, which return it to the heart