7.6 - Blood vessels an their functions

• What are the 4 blood vessels ?

  Arteries, veins, capillaries, arterioles
• What do arterioles do ?

  Control blood flow from arteries to capillaries
• What are the 5 layers that arteries, veins and arterioles have ?

  Tough fibrous layer, muscle, elastic layer, endothelium (inner lining), lumen
• What’s the function of the tough fibrous outer layer ?

  Resist internal and external pressure changes
• What’s the function of the muscle layer ?

  Constricts and dilates the vessel to control blood flow
• What’s the function of the elastic layer ?

  Stretches and recoils to maintain blood pressure
• What’s the function of the endothelium ?

  Smooth to reduce friction
• What layers do capillaries have ?

  Endothelium and lumen
• 4 ways in which artery structure is different to veins and how this helps with its function ?

  • Thicker muscle than veins - blood at higher pressure so can constrict and dilate to control volume of blood into arterioles
  • Thicker elastic layer than veins - stretch and recoils allows high pressure to be maintained
  • Thicker wall - ensures no bursting under high pressure
  • No valves - blood unlikely to back flow as at constant high pressure
• 2 ways in which arterioles structure is different to arteries and how it helps with their function ?

  • Thicker muscle than arteries - allows lumen to constrict to restrict and control blood flow into capillaries
  • Thinner elastic layer than arteries - more area so at lower pressure, not a much stretch or recoils allows high needed
• 4 ways in which vein structure is different to arteries and how this helps their function ?

  • Thinner muscle - blood not at high pressure, carry away from tissues
  • Thinner elastic - lower pressure, no need to stretch or recoil
  • Less thick walls - low pressure, allows flattening during skeletal contraction
  • Valves - low pressure so prevents backflow of blood
• 4 ways in which capillaries structure aids their function ?

  • Walls are mostly endothelium - thin so shorter diffusion distance for rapid diffusion
  • Numerous and highly branched - provides a larger surface area for exchange
  • Narrow lumen - squeezes RBCs against walls, reducing diff distance
  • Spaces between endothelial cells - all WBCs to move out and fight infection in tissues and tissue fluid formation
• What pressure does the pumping of the heart create?

  Hydrostatic pressure
• What is tissue fluid formed by ?

  The ultrafiltration of blood plasma
• Explain how tissue fluid is formed and returned back to the circulatory system

  • Ventricular systole means hydrostatic pressure is high at arterial end of capillaries
  • pressure causes small molecules (oxygen, water, ions, AA, glucose) to move out of blood plasma by ultrafiltration
  • hydrostatic pressure and water potential in the capillary is now lower than the tissue fluid outside
  • so water is forced back into capillary at venule end by the higher hydrostatic pressure also water leaves tissue fluid and enters blood via osmosis down a water potential gradient
• How is excess tissue fluid returned to the circulatory system ?

  • carried back in the lymphatic system
  • Drains into blood via 2 ducts into veins close to the heart
• In what 2 ways is the contents of the lymphatic system moved ?

  • Hydrostatic pressure of tissue fluid that left the capillaries
  • Contraction of body muscles squeeze lymph vessels