Unit 1 Section 5.4 Blood Vessels

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  • Blood Vessels
    • Arteries, Capillaries and Veins
      • Arteries
        • arteries carry blood from the heart to the rest of the body. their walls are thick and muscular and have elastic tissue to cope with the high pressure produced by the heartbeat
        • The inner lining is folded, allowing the artery to expand - this also helps it to cope with high pressure, all arteries carry oxygenated blood except for the pulmonary arteries, which take deoxygenated blood to the lungs
      • Capillaries
        • arteries branch into capillaries, which are the smallest of the blood vessels. substances like glucose and oxygen are exchanged between cells and capillaries, so they are adapted for sufficient diffusion
      • Veins
        • veins take blood back to the heart under low pressure. they're wider than equivalent arteries, very little elastic or muscle tissue.
        • veins contain valves to stop the blood flowing backwards. blood flow through the veins is helped by contraction of the body muscles surrounding them.
        • all veins carry deoxygenated blood. except for pulmonary veins, which carry oxygenated blood to the heart from the lungs
    • Tissue Fluid
      • is the fluid that surrounds cells in tissues. its made from substances that leave the blood
      • cells take in oxygen and nutrients from tissue fluid, and release metabolic waste into it
      • In a capillary bed substances move out of the capillaries, into the tissue fluid, by pressure filtration
      • Pressure Filtration
        • at the start of the capillary bed, nearest the arteries, the hydrostatic pressure inside the capillaries is greater than the pressure in the tissue fluid
        • This Difference in pressure forces fluid out of the capillaries and into the spaces around the cells, forming tissue fluid
        • as fluid leaves, the pressure reduced in the capillaries - so the pressure is much lower at the end of the capillary bed that's nearest to the veins
        • due to the fluid loss, the water potential at the end of the capillaries is nearest the veins is lower than the water potential in the tissue fluid
          • so some water re-enters the capillaries from the tissue fluid at the vein end by osmosis
    • Lymph Vessels
      • Not all of the tissue fluid re - enters the capillaries at the vain end of the capillary bed.
        • some excess tissue fluid is left over. this extra fluid eventually gets returned to the blood through the lymphatic system
          • the lymphatic system is a kind of drainage system made up of lymph vessels
      • the smallest lymph vessels are the lymph capillaries
      • excess tissue fluid passes into lymph vessels
        • once inside its called lymph, valves in the lymph vessels stop the lymph going backwards
    • Blood, Tissue Fluid and Lymph
      • Blood Tissue Fluid and lymph are all quite similar - tissue fluid is formed from blood and lymph is formed from tissue fluid. the main differences are shown in the table


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