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Biology as level question? Tissue fluid watch

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    why is the volume of your blood greater going into your capillaries than it is when it goes into your veins?

    I dont really know how to answer this question, with reference to tissue fluid and ultrafiltration. Help?
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    (Original post by jakestevens70)
    why is the volume of your blood greater going into your capillaries than it is when it goes into your veins?

    I dont really know how to answer this question, with reference to tissue fluid and ultrafiltration. Help?
    I would have thought that the tissue fluid is pushed out of the capillaries and it bathes the cells and some of it is taken away by the lymphatic system? So less liquid overall?
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    So shouldnt there be less blood going to capillaries?
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    Tissue fluid is formed when the blood is moving under high pressure in the arterioles and some materials will be forced through capillaries into the space between the cells where they will be up-taken. However, when those materials leave the arterioles end, some water will move into the tissue, meaning that the water potential in the arterioles end is lower than the tissue (This is also due to the presence of plasma proteins) . Hence there will be an osmotic effect inwards (towards the arterioles end). However, the hydrostatic pressure in the arterioles is greater than the osmotic effect. So, there will be an overall flow of water outwards.

    In the venous end, the blood will be moving at much lower pressure. However, since the plasma proteins are still present, they will lower the water potential. Obviously the tissue will have a higher WP and so water will move into blood via osmosis from high to low across the capillaries. This means the osmotic effect will be greater than the hydrostatic pressure. Hence, there will be a net outflow of water to the blood.

    Any other wastes like Carbon Dioxide will be drained into the lymph vessels that have lymph which is part of the lymphatic system. These connect to a vein that is nearby the heart. This is done via the thoracic duct.

    I hope this helps - I recalled all this from memory...
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    Cheers mate, so what would i put as a 3 mark answer then for this?
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    Well, 3 marks ! I don't really know - However, I think they are looking for:

    1) Blood contains other things like water, oxygen, glucose, etc...
    2) These increase the volume of the blood.
    3) However as these materials are moving under high pressure in the arterioles, they are forced out into the tissue through capillaries.
    4) This means the blood is carrying less materials (Volume decreases)
    5) Hence, the volume at the venous end is lower.

    I think that should be enough - However, try to compare my answer with others and get the best one out.
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    thats great thanks!! anyone else got any others to compare?
 
 
 
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