Blood vessels 2

• Arteries carry blood away from blood and into arterioles
• Arterioles

  smaller arteries that control blood flow from arteries to capillaries
• Capillaries

  Tiny vessels linking arterioles to veins
• Veins

  Carry blood from capillaries back to the heart
• Arteries arterioles and veins all have the same structure but different relative proportions of each other

  • Tough fibrous outer layer: resist pressure changes
  • Muscle layer: contract to control blood flow
  • Elastic layer: maintain blood pressure by stretching and recoiling
  • Think inner lining (endothelium) : smooth reducing friction and thin for diffusion
  • Lumen: central cavity of blood vessels through where blood flows
• Artery FUNCTION

  Transport blood rapidly under high pressure from heart to tissues
• Arteries STRUCTURE

  • Thick muscle layer: smaller arteries constricted and dilated to control volume of blood passing
  • Thick elastic layer: high blood pressure important in arteries, stretching and recoil maintain pressure. Systole elastic stretch, recoil diastole (relax)
  • Thick wall: prevents bursting from high pressure
  • No valves, blood flow constant high pressure, no backflow
• Arterioles FUNCTION

  Carry blood under lower pressure than arteries from artery to capillary, controlling flow of blood
• Arterioles STRUCTURE

  • Thicker muscle layer than arteries: contraction of muscle layer allow constriction of lumen = restricting blood flow, controlling movement into capillaries
  • This elastic layer: Lower blood pressure
• Vein FUNCTION

  Transports blood slowly under low pressure from capillaries in tissue to heart
• Vein STRUCTURE

  • Thin muscle layer, vein carry blood away from tissues so constriction and dilation cannot control blood flow to tissues
  • Thin elastic layer: lower blood pressure so won't burst
  • Small thickness of wall: pressure too low to burst, aids flow of blood as they flatten easily
  • Valves due to low pressure
• Capillary FUNCTION

  Exchanges metabolic materials egg oxygen, glucose and carbon dioxide between blood and cells. Blood flow is slower allowing time to exchange materials
• Capillaries STRUCTURE

  • Thin wall consisting only of lining layer: short diffusion pathway
  • Numerous and branched: large surface area for exchange
  • Narrow diameter: No cell too far from capillary and short diffusion pathway
  • Narrow lumen: Red blood cell squeezed flat against side of capillary, close to the cell in which is supplying oxygen to, reduced diffusion distance
  • Spaces in lining (endothelial) allow white blood cells to escape to deal with infection in tissues.