Carbon dioxide is carried in the blood mainly as

Options

A. Sodium bicarbonate
B. Potassium bicarbonate
C. Carbamino- haemoglobin
D. Dissolved gas in plasma

Answer

To answer the question "Carbon dioxide is carried in the blood mainly as," we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding Carbon Dioxide Transport**: Carbon dioxide (CO2) is produced by cells during metabolism and needs to be transported back to the lungs for exhalation.

2. **Dissolution in Plasma**: A small percentage of CO2 (about 7%) is dissolved directly in the blood plasma. This is the first method of transport.

3. **Formation of Carboamino Compounds**: Another portion of CO2 (approximately 23%) binds to hemoglobin and other proteins in red blood cells to form carbamino compounds, specifically known as carboaminohemoglobin.

4. **Majority as Bicarbonate**: The majority of CO2 (about 70%) is converted into bicarbonate ions (HCO3-) in the presence of water and the enzyme carbonic anhydrase. This reaction can be summarized as follows:
- CO2 + H2O ⇌ H2CO3 (carbonic acid)
- H2CO3 ⇌ H+ + HCO3- (bicarbonate ion)

5. **Bicarbonate Ion Transport**: The bicarbonate ion (HCO3-) then moves out of the red blood cells into the plasma. To maintain electrical neutrality, chloride ions (Cl-) move into the red blood cells, a process known as the "chloride shift" or "Hamburger effect."

6. **Conclusion**: The majority of carbon dioxide in the blood is carried as sodium bicarbonate (NaHCO3), which is formed when bicarbonate ions react with sodium ions in the plasma.

### Final Answer:
Carbon dioxide is carried in the blood mainly as sodium bicarbonate.

---