Tissue fluid

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  • Created by: Laura
  • Created on: 04-05-14 13:48
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  • Tissue fluid and its formation
    • Tissue fluid is a watery liquid that contains glucose, amino acids, fatty acids, salts and oxygen.
    • Formation of tissue fluid
      • Blood pumped by the heart passes along arteries, arterioles and then capillaries. This creates a pressure called hydrostatic pressure
      • This hydrostatic pressure forces tissue fluid out the blood plasma. This pressure however is opposed by two things
        • Hydrostatic pressure of the tissue fluid outside the capillaries, which prevents outward movement of liquid
        • The lower water potential of the blood die to the plasma proteins, that pulls water back into the blood within the capillaries
      • The combined effect of all these forces is to create an overall pressure that pushes tissue fluid out of the capillaries.
        • This pressure is only enough to force small molecules out of the capillaries, leaving all cells and proteins in the blood. this is called ultrafiltration
    • Return of tissue fluid to the circulatory system
      • Once tissue fluid has exchanged metabolic materials with the cells it bathes, it must be returned to the circulatory system
      • Most tissue fluid returns to the blood plasma directly via the capillaries. It returns as follows
        • The loss of tissue fluid from the capillaries reduces the hydrostatic pressure inside them
          • By the time the blood has reached the venous end of the capillary network its hydrated pressure is less than that of the tissue fluid outside
            • Therefore tissue fluid is forced back into the capillaries by the higher hydrostatic pressure outside them
              • In addition the osmotic forces resulting form the proteins in the blood plasma pull water back into the capillaries
      • The tissue fluid has lost most of its oxygen and nutrients by diffusion into the cell that it bathed, but it has gained carbon dioxide and waste materials
      • Not all the tissue fluid can return to the capillaries, the remainder is carried back via the lymphatic system
        • This is a system of vessels that begin in the tissues. Initially they resemble capillaries but they gradually merge into larger vessels that form a network throughout the body
          • These larger vessels drain their contemns back into the bloodsteam via two ducts that join veins close to the heart
            • Contents of the lymph are not moved by the pumping of the heart they are moved by hydrostatic pressure of the tissue fluid that has left the capillaries and the contraction of body muscle that squeeze the lymph vessels
  • Not all the tissue fluid can return to the capillaries, the remainder is carried back via the lymphatic system
    • This is a system of vessels that begin in the tissues. Initially they resemble capillaries but they gradually merge into larger vessels that form a network throughout the body
      • These larger vessels drain their contemns back into the bloodsteam via two ducts that join veins close to the heart
        • Contents of the lymph are not moved by the pumping of the heart they are moved by hydrostatic pressure of the tissue fluid that has left the capillaries and the contraction of body muscle that squeeze the lymph vessels

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