Transport of carbon dioxide
| English | Chinese | Pinyin |
|---|---|---|
| carbonic anhydrase | 碳酸酐酶 | tàn suān gān méi |
| carbonic acid | 碳酸 | tàn suān |
| hydrogencarbonate | 碳酸氢根 | tàn suān qīng gēn |
| chloride shift | 氯转移 | lǜ zhuǎn yí |
| carbaminohaemoglobin | 氨甲酰血红蛋白 | ān jiǎ xiān xuè hóng dàn bái |
| buffer | 缓冲 | huǎn chōng |
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.
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:
The largest share is carried as hydrogencarbonate ions in the plasma.
The enzyme carbonic anhydrase speeds up the reaction of:
Carbonic anhydrase catalyses CO₂ + water → carbonic acid, inside the red blood cell.
Match each term to its role in carrying CO₂.
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 INTO the red blood cell to balance the charge as hydrogencarbonate ions leave.
As negative HCO₃⁻ ions exit, negative chloride ions move in to keep the electrical charge balanced.
The hydrogen ions produced are dealt with by:
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.
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