Blood Vessel Structure Related to Function

Tough Outer Collagen Layer

• The outer collagen layer is tough and prevents the artery from rupturing at high pressure

Thick layer of Elastic Fibres

• elastic tissue stretches under pressure when the heart contracts
• it then recoils
• this evens out blood pressure/blood flow

Thick layer of Muscle

• The muscle contracts
• this reduces the diameter of the lumen
• in this way the artery can change blood flow/ pressure

Epithelium

• epithelium is smooth which reduces friction so there are fewer blood clots

Veins

• same collagen layer as arteries
• they have a wider lumen than equivelent arteries
  • This is because they have less elastic and muscle fibre in their walls
  • they have less of this tissue since they don't need to accomodate high pressure as blood pressure in the veins is low
  • this is because they are carrying blood to the heart, rather than away from it
  • Veins also contain Valves to prevent backflow of blood
  • Same endothelium

Capillaries

• have no outer layer of collagen fibres
• Capillaries have no muscle or elastic tissue since they don't accomodate high pressure
• Capillaries have a very thin endothelium which decreases the diffusion pathway, making them adapted for gas exchange via diffusion.