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Why does blood clot when removed?

  1. Jun 29, 2010 #1
    Hello everyone,

    If blood is taken to a tube it clots after a while. If the tube is glass, since it is a wettable surface the process is hastened, but my question is normally in the body when blood is flowing, anticoagulents are dominant over coagulents. Now if the blood is moving slow inside the body or out, why do coagulents become more dominant.

    Also in capillaries there is only endothelium right no collagen. So how do platelets bind if a capillary wall is damaged, platelets bind to collagen right?

    Thanks a lot :smile:
    Last edited: Jun 29, 2010
  2. jcsd
  3. Jun 29, 2010 #2
    Blood clotting occurs after the blood is exposed to certain proteins outside the endothelium. This is what you would need to look at to understand why blood clots in a test tube:

    Now it's important to differentiate between blood drying and blood clotting, they are different. Is the speed of the blood flowing a factor in clotting? I'm not sure, I don't think so though. I think the amount of clotting found in a test tube is negligible, especially in ones that have anti-coagulation mixtures in them. (If properly used).

    The collagen question is answered if you follow the way blood clots. Collagen is extremely abundant in the human body and it is recruited by von Willebrand Factor. It also recruits other things but if you follow the links above I think it should clear up the questions you've asked.

    If not just holler :)
  4. Jun 30, 2010 #3
    Thanks for the help :smile: I read about the things you have mentioned however I'm still little bit off in my thinking. Ok so if you get some blood into a test tube, where does the trauma occur. I mean the surrounding vessel is not damaged, I just put some blood into a test tube, what creates the trauma and make platelets release tissue factor.

    Also a capillary is made only of endothelium, so how can platelets bind to sub endothelium collagen creating intrinsic pathway, in capillaries does extrinisic pathway take place. Thanks again :smile:
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