Carbon dioxide enters a red blood cell in a tissue capillary…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Carbon dioxide enters a red blood cell in a tissue capillary.
- Which enzyme acts on carbon dioxide and water in the cell?
- Name the acid that forms first, and the two ions that it gives.
- What happens to the bicarbonate ions, and which ion moves in as they move out?
- What does the same reaction do in the alveolar capillaries?
Need a reminder? The key ideaShow
Carbon dioxide travels about per cent as bicarbonate, to per cent as carbamino-haemoglobin and about per cent dissolved. Carbonic anhydrase of the red blood cells makes go forward in the tissues and backward in the alveoli. Each mL of deoxygenated blood delivers about mL of carbon dioxide.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Carbonic anhydrase.
Step 2. (b) Carbonic acid, HCO, forms first. It gives a hydrogen ion and a bicarbonate ion.
Step 3. (c) Most bicarbonate ions move out of the cell into the plasma. Chloride ions move in as they move out. This is the chloride shift.
Step 4. (d) In the alveolar capillaries the pCO is low, so the reaction runs backward. Carbon dioxide and water are formed, and the carbon dioxide is released to the alveoli.
Answer: (a) carbonic anhydrase; (b) carbonic acid, giving H and HCO; (c) bicarbonate moves out, chloride moves in; (d) it runs backward and releases carbon dioxide.
Watch out. The enzyme does not decide the direction. The partial pressure of carbon dioxide does.
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