Veins

• Veins


  Blood vessels that carry deoxygenated blood to the heart
• Structure of veins


  • Thinner walls than arteries
  • Larger lumen than arteries
  • Carry greater volume of blood than arteries
  • Smooth muscle and elastic layers are thinner than in arteries
  • No elastic recoil
• Veins have an internal lining of endothelial cells which reduces friction between the blood and the vein wall
• Valves in veins


  Help keep the blood moving in the forward direction towards the heart
• How valves in veins work

  1. Muscles squeezing the veins forces the blood along

  2. If blood moves forward, valves remain open

  3. If blood starts to move backwards, valves shut
• When we inhale


  The decrease in chest cavity pressure helps the blood in the chest veins move towards the heart
• The structure of veins is adapted to their function of carrying deoxygenated blood back to the heart at low pressure
• Veins


  • Have thinner muscle layer than arteries / arterioles and so have thinner walls
  • Have large diameter (lumen) than arteries
  • Have reduced pressure to arteries
  • Have valves to ensure blood flow is in one direction only
• Tunica Media


  • Lumen
  • Smooth muscle + elastic tissue
• Tunica Adventitia


  • Outer layer
  • Elastic + collagen fibres
• Tunica Intima


  Layer of endothelium cells