blood vessels

• arteries:

  • carry blood away from heart to rest of body
  • thick, muscular walls and elastic tissue to stretch and recoil as the heart beats, which helps maintain high pressure
  • the inner lining (endothelium) is folded, allowing the artery to expand to maintain high pressure
• arterioles:

  • arteries branch into arterioles, which are much smaller
  • layer of smooth muscle but less elastic tissue
  • smooth muscle allows them to expand or contract, controlling the amount of blood that flows into tissues
• capillaries:

  • arterioles branch into capillaries --> smallest blood vessel
  • substances like glucose and oxygen are exchanged between cells and capillaries
  • one cell thick = efficient diffusion + thin lumen = one RBC passes at a time
• capillaries connect into venules, which have thin walls that can contain some muscle cells. venules join together to form veins
• veins:

  • take blood back to the heart under low pressure
  • wider lumen than arteries, with very little elastic or muscle tissue
  • veins contain valves to stop the backflow of blood
  • blood flow through the veins is helped by the contraction of the body muscles surrounding them