Blood vessels

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  • Created by: Laura
  • Created on: 03-05-14 21:25
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  • Blood vessels and their functions
    • Arteries - carry blood rapidly away from the heart under high pressure and into arterioles
      • Thick muscle layer - this means arteries can be constricted and dilated in order to control the volume of blood passing through them
      • Thick elastic layer - important that blood pressure in arteries is kept high if blood is to reach the extremities of the body. The elastic layer is stretched at every beat of the heart, this creates high pressure
      • Overall thickness of the wall is large - resists vessel bursting under pressure
      • There are no valves - (except in arteries leaving the heart) because blood is under constant high pressure and therefore does not tend to flow backwards
    • Arterioles - are smaller arteries that carry and control blood flow, under low pressure, from arteries to capillaries
      • Muscle layer thicker than in arteries - this allows constriction of the lumen which restricts the flow of blood
      • Thinner elastic layer than arteries - because blood pressure is lower
    • Capillaries - are tiny vessels that link arteries to veins
      • Walls consist only of the lining layer - makes them extremely thin so the distance for diffusion is short. This allows for rapid diffusion of materials from blood to cells
      • Numerous and highly branched - large surface area for diffusion
      • They have a narrow diameter - so permeate tissues  which means no cell is far from a capillary
      • There are spaces between the lining cells - allow white blood cells to escape in order to deal with infections within tissues
    • Veins - carry blood from capillaries back to the heart
      • Thin muscle layer - carry blood away from tissues so no need to control flow of blood to them
      • Thin elastic layer - low pressure of blood will not cause them to burst
      • there are valves throughout - to ensure blood does not flow backwards as blood pressure is so low


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