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Friday 24th October 2014
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How do blood cells know to let go of oxygen in the right place?

Question

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

Answer

** Definitive **
Name: Professor Hal
Qualification: Mystery Hourís Resident Agony Uncle
Answer: Itís 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 Ė if it stuck to it permanently, it wouldnít 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. Thatís how it knows.

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