Blood vessels

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  • Created by: Steff06
  • Created on: 12-04-16 10:26
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  • Blood vessels
    • In an OPEN circulatory system, the blood is NOT always in vessels. In a CLOSED circulatory system, the blood always remains in vessels.
    • Not all animals have an open system, because LARGER organisms rely on blood to transport oxygen and carbon dioxide. Blood remains at LOW PRESSURE in an open circulatory system and flow is slow.
      • This would be INSUFFICIENT to supply the needs of muscles in a large, active animal and other parts of the body may not receive sufficient oxygen or nutrients.
    • Closed circulatory systems: TISSUE FLUID bathes the tissues and cells. Enables heart to pump blood at HIGHER pressure so it flows more quickly. This means it can deliver oxygen and nutrients quicker and remove CO2 and wastes more quickly.
    • Fish have a CLOSED, SINGLE circulation which means blood remains in vessels that carry it on a single pathway. Exchange surfaces at gills and body tissues to allow exchange of materials.
    • Blood vessels:
      • All have an INNER LAYER or lining, made from a single layer of cells called the ENDOTHELIUM. This is a THIN layer that is SMOOTH to reduce friction with flowing blood.
    • Arteries:
      • Carry blood AWAY from the heart. Blood is at HIGH PRESSURE, so artery wall must be able to withstand this.
      • LUMEN is SMALL to maintain HIGH pressure. Wall is THICK and contains COLLAGEN to give it STRENGTH to withstand pressure.
      • Wall has ELASTIC TISSUE that allows wall to STRETCH + RECOIL when the heart pumps. Recoil maintains HIGH pressure.
      • Wall contains SMOOTH muscle that can contract+constrict artery. Constriction NARROWS lumen. ENDOTHELIUM is FOLDED+can unfold when artery stretches.
    • Veins:
      • Carry blood TO the heart. Blood is at LOW pressure+walls do not need to be thick. LUMEN is LARGE to ease flow of blood. Walls have THINNER layers of COLLAGEN, SMOOTH MUSCLE+ELASTIC TISSUE.
      • Walls do NOT need to stretch+recoil+are not constricted to reduce blood flow. Contain VALVES to help blood flow back TO HEART+prevent it flowing in OPPOSITE direction.
      • As walls are THIN, vein can be FLATTENED by action of skeletal muscle. Pressure applied to blood, forcing blood to move along in a direction dictated by valves.
    • Capillaries:
      • Very THIN WALLS. Allow EXCHANGE of materials between BLOOD and cells of TIISSUES via TISSUE FLUID.
        • Walls consist of a SINGLE LAYER of FLATTENED ENDOTHELIAL CELLS that REDUCES diffusion distance for exchange of materials.
      • LUMEN is very NARROW  to ensure RED BLOOD CELLS are SQUEEZED as they pass along capillaries.
        • This helps them give up oxygen as it presses them close to capillary wall, REDUCING DIFFUSION PATH to tissues.


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