Arteries, Veins and Capillaries

• • Vessel: Artery
  • Function: Transport high pressure blood away from heart
  • Structure:
  • Elastic walls expand and relax as blood is forced out; causes pulse
  • Thick walls withstand high pressure
  • Rings of muscle narrow or widen artery to control blood flow.
• • Vessel: Vein
  • Function: Transport low pressure blood to the heart
  • Structure:
  • Valves prevent backflow of blood.
  • Blood is at low pressure, but nearby muscles squeeze veins and help push blood to the heart
  • Large diameter and thin walls reduce resistance to flow of blood
• • Vessel: Capillary
  • Function: Allow substances to diffuse into cells
  • Structure:
  • One cell thick wall for easy diffusion
  • Highly branched; large surface area
  • Capillary beds constantly supplied with fresh blood, so diffusion occurs