Blood, Tissue Fluid and Lymph

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  • Blood, Tissue Fluid & Lymph
    • Blood
      • consists of a watery fluid called plasma - containing many dissolved substances (O2, CO2, salts, plasma proteins, glucose etc)
      • contains red blood cells (erythrocytes) and white blood cells (leucocytes) and platelets
    • Tissue Fluid
      • transports oxygen and nutrients from the blood to the cells and CO2 and waste products to the blood
      • artery reaches tissues and branches into smaller arterioles, then into a network of capillaries
        • blood under high pressure due to contraction of the heart - hydrostatic pressure
          • tends to push the blood out of the capillaries through tiny holes in their walls
            • the fluid that leaves consists of plasma with dissolved nutrients and oxygen and occasionally a few white blood cells
              • everything else is too large to pass through the holes
                • fluid surrounds the cells so that gaseous exchange can occur across cell surface membranes
                  • tissue fluid has some hydrostatic pressure which will tend to push the fluid back into the capillaries
                    • both the blood and the fluid also contain solutes, giving them a negative water potential - the tissue fluids is less negative than the bloods
                      • water moves back into the blood via osmosis
                        • at the other end of the capillaries, the blood reaches venules (that lead to veins)
                          • here the blood has lost its hydrostatic pressure - combined with the hydrostatic pressure in the tissue fluid and the osmotic force of the plasma proteins fluid moves back into the capillary
                            • it carries dissolved substances such as CO2
    • Lymph
      • the tissue fluid that doesn't return to the capillaries is drained away into the lymphatic system
        • it is drained via tubes similar to capillaries from the tissues to the blood system in the chest cavity
      • contains same solutes as tissue fluid - less O2/nutrients, more CO2/waste
        • more fatty material that has been absorbed from the intestines
      • contains many lymphocytes, produced in the lymph nodes that are swellings found at intervals along the system, that filter any bacteria and foreign material from the lymph fluid
        • phagocytes can then engulf and destroy these bacteria and foreign particles


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