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Why does reduced blood flow in veins cause numbness?

  1. Oct 21, 2009 #1
    Last topic I made was misunderstood and locked so basically what I want to know is the mechanism behind numbness in legs. I don't have a numbness problem or seeking medical advice.

    If veins have reduced blood flow how does this create numbness. The nerves are still supplied by the arteries. If veins have reduced flow are arteries also affected. Isn't it reduced artery flow that creates numbness, how does veins cause it.

    Thanks :smile:
     
  2. jcsd
  3. Oct 21, 2009 #2
    Veins carry oxygen-poor blood cells back to the heart and lungs to be re-oxygenated, so it is reduced blood flow in the arteries that can cause a drop in sensation in the legs, arms, hands, etc. Arteries contain freshly oxygenated blood and carry it throughout the body. As you mentioned, it is the capillaries that directly provide the nutrients to nerve cells which in turn allows for signal transduction to occur, but it is the arteries that supply the capillaries with fresh blood.

    Nerve cells require a continuous flow of nutrients, especially Ca2+ and Na+ ions in order to properly function. As you may recall, nerve signal transduction depends on the nerve cell being able to route a wave of depolarization across the length of the axon. Without the vital nutrients and oxygen that fresh blood supplies, the electrical gradient can't be produced, resulting in no signal being sent to the brain. Your body interprets this lack of signal as numbness. You can try this out on your own by pressing against the large artery on the inside of your upper arm. After a few minutes you'll notice a drop in the sensation of your entire limb, which is due to your nerve cells not having fresh nutrients.

    As for veins, blocking a vein will only lower the amount of blood that is being re-oxygenated, but there are hundreds of veins in your body that can compensate for a single vein being blocked, so it is very unlikely that blocking a single vein will have any effect. The only way that vein blockage could cause problem is if it is completely blocked off, resulting in a buildup of oxygen-poor blood not being able to leave a site, at which point numbness will be the least of your worries, and gas gangrene and swelling will become more pressing issues.
     
  4. Oct 21, 2009 #3
    Nicely explained :smile: Thanks :smile:
     
  5. Oct 24, 2009 #4

    Moonbear

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    Can you explain more clearly what you mean by reduced blood flow in veins? I can think of several different scenarios that could potentially be described that way, and the answer would be different for each one. For example, do you mean pooling of blood in veins, such as with varicose veins when the blood runs backward through defective valves, or do you mean a blood clot within the veins, or could you mean lack of blood getting to the veins (which might imply there is also a reduced arterial flow)?
     
  6. Oct 25, 2009 #5
    Any of the examples you gave would be good ones to illustrate what is meant by reduced blood flow in veins. I wasn't referring to any specific cause for reduced blood flow in veins, just saying that, in the event of reduced blood flow, those symptoms would be what would result.
     
  7. Oct 29, 2009 #6

    Moonbear

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    Your answer is not complete in the case of a blocked vein or veins with incompetent valves, only in terms of an arterial source of reduced blood flow, which is why I'm trying to find out from the OP which condition s/he is referring to.
     
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