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Thursday 1st September 2016
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How do blood cells know to let go of oxygen in the right place?


Blood cells go through the lungs, picking up oxygen and picking up carbon dioxide, then do the opposite in the muscles. How does the blood cell know when pick up and let go of the oxygen?
Chris, Berkhamstead


** Definitive **
Name: Professor Hal
Qualification: Mystery Hour’s Resident Agony Uncle
Answer: It’s to do with oxygen-binding efficiency. Blood cells have a haem group, which is what gives them their colour.  In the lungs, there is a high oxygen tension and a low carbon-dioxide tension.  Haem is created to get oxygen to stick to it, just enough for it to be transportable – if it stuck to it permanently, it wouldn’t come off at the other end.  When it gets to the respiring cells, it drops off the oxygen because respiring cells create carbon dioxide and carbon dioxide when it dissolves in plasma causes carbonic acid, so the PH changes. When there is acid, haem is less able to stick to oxygen so it starts unloading the oxygen. That’s how it knows.

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