Transport of carbon dioxide
Introduced| English | Meaning |
|---|---|
| carbonic anhydrase/kɑːˈbɒnɪk ˈænhaɪdreɪz/ | The red-cell enzyme that rapidly converts carbon dioxide and water to carbonic acid. |
| carbonic acid/kɑːˈbɒnɪk ˈæsɪd/ | The weak acid formed when carbon dioxide reacts with water, in equilibrium with hydrogen and hydrogencarbonate ions. |
| hydrogencarbonate/ˈhaɪdrəʊdʒeŋkɑːbɒneɪt/ | hydrogencarbonate |
| chloride shift/ˈklɔːraɪd ʃɪft/ | The movement of chloride ions into red blood cells to balance charge as hydrogencarbonate leaves. |
| carbaminohaemoglobin/ˌkɑːbəˌmɪnəʊˌhiːməˈɡləʊbɪn/ | Haemoglobin with carbon dioxide bound to amino groups on its protein chains, forming one means of carbon dioxide transport. |
| buffer/ˈbʌfə/ | A substance or solution that limits changes in pH when small amounts of acid or base are added. |
Carrying carbon dioxide
- Carbon dioxide made by respiring cells must be carried to the lungs.
- A little dissolves in the plasma — but most is carried a cleverer way.
- The action happens inside the red blood cells.
Most carbon dioxide is carried in the blood as ______ ions in the plasma.
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Formed from CO₂ and water in the red blood cells, then carried in the plasma.
The reaction in red blood cells
- the enzyme carbonic anhydrase 碳酸酐酶 speeds up: carbon dioxide + water → carbonic acid 碳酸.
- the carbonic acid splits into hydrogen ions and hydrogencarbonate 碳酸氢根 ions.
- the hydrogencarbonate ions move out into the plasma — this is the main way CO₂ is carried.
Most CO₂ travels as hydrogencarbonate ions, made in the red blood cells by carbonic anhydrase
Most carbon dioxide is carried in the blood as:
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The largest share is carried as hydrogencarbonate ions in the plasma.
The enzyme carbonic anhydrase speeds up the reaction of:
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Carbonic anhydrase catalyses CO₂ + water → carbonic acid, inside the red blood cell.
Match each term to its role in carrying CO₂.
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The enzyme makes carbonic acid; it splits into H⁺ and HCO₃⁻; chloride balances the charge; haemoglobin buffers the H⁺.
The chloride shift 氯转移
- As negative hydrogencarbonate ions leave, chloride ions move in to keep the charge balanced — the chloride shift.
- The leftover hydrogen ions join haemoglobin to form haemoglobinic acid — this mops them up and keeps the pH steady.
- Some CO₂ also joins haemoglobin directly as carbaminohaemoglobin 氨甲酰血红蛋白.
Carrying carbon dioxide
Step through what happens to CO₂ in a red blood cell — most of it ends up as hydrogencarbonate in the plasma.
In the chloride shift, chloride ions move OUT of the red blood cell as hydrogencarbonate ions leave.
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False. As negative HCO₃⁻ ions leave the red blood cell, negative chloride ions move in to balance the charge.
The hydrogen ions produced are dealt with by:
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H⁺ binds haemoglobin (haemoglobinic acid), buffering the blood so the pH does not fall sharply.
Put the journey of CO₂ in a red blood cell in order.
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CO₂ in → carbonic acid → splits → HCO₃⁻ out (chloride in) → H⁺ buffered.
Carbon dioxide and blood pH
- Dissolved CO₂ forms carbonic acid, which would lower blood pH.
- Haemoglobin buffers 缓冲 the hydrogen ions, keeping the blood pH stable as CO₂ is carried.
You've got it
- most CO₂ is carried as hydrogencarbonate ions in the plasma
- carbonic anhydrase: CO₂ + water → carbonic acid → H⁺ + hydrogencarbonate
- chloride shift: chloride ions move in as hydrogencarbonate moves out (balances charge)
- H⁺ joins haemoglobin (haemoglobinic acid) to buffer pH; some CO₂ → carbaminohaemoglobin
Write from the chloride shift
- Carbon dioxide enters a red blood cell.
- Hydrogencarbonate ions then leave the cell.
What enters to balance the charge?
Chloride replaces the negative ions that leave.
What enters the red blood cell in the chloride shift?
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Chloride balances the hydrogencarbonate that leaves.