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Within ourselves, does blood have an expiry date?

  1. Mar 4, 2009 #1
    I would assume that blood, within us, is only good for so long but, I could be wrong. Also, if it does become "bad", where does it go? How do we get rid of "garbage blood"?
  2. jcsd
  3. Mar 4, 2009 #2


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    Red blood cells last about 3 months and then die. They are expelled in the feces. That is partly what gives feces its characteristic colour.

    (BTW, thier limited lifespan is of great use to Diabetics. Sugar buillds up in the Hemoglobin of RBCs in direct proportion to its levels in the body. As these RBCs are replenished, their concentration reflects a history of the body's sugar levels. By doing a test callled HbA1c, doctors can get a very good idea of how a patient's blood sugars have been doing over the previous three months. This is of much greater use than any number of on-the-spot tests.)
  4. Mar 5, 2009 #3

    Andy Resnick

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    The plasma is circulated through the kidneys (25% of the blood is directed there), corresponding to 130 liters/day. Molecules smaller than (approximately) albumin enter the ultrafiltrate and pass through nephrons, where material is selectively reabsorbed to maintain homeostasis, and waste products (small molecules like urea, sodium, etc) excreted.

    That's a good question about other blood products- lymphocytes, macrophages, neutrophils, all kinds of cells, cell fragments, proteins, lipoproteins... circulate. I don't know how material passes from the blood to the gut. That's actually a really good question....
  5. Mar 5, 2009 #4

    Andy Resnick

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    I took this over to a colleague and discussed.

    Ok- there are two main routes of things out of the body, either via the kidney or via the liver (bile acids). Cellular debris, from lysed cells or whatever, is processed in the liver and broken back down into the elemental components- the same process happens, to some degree, in each cell (proteosomes, lysosomes, endosomes..) and the components re-used as much as possible.

    Fat soluable wastes in particular, are put into the bile and excreted into the ileum and moves along the gut. Hemoglobin is broken down in the liver and re-used; the 'life cycle' of iron in the body is marginally understood.

    What's amazing is not how little we know, it's how much we *do* know.
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