Bulk of carbon dioxide `(CO_(2))` released from body tissues into the blood is present as

Options

A. bicarbonate in blood plasma and RBCs
B. free `CO_(2)` in blood plasma
C. 70% carbamino-haemoglobin and 30% as bicarbonate
D. carbomino-haemoglobin in RBCs

Answer

To determine the bulk of carbon dioxide (CO₂) released from body tissues into the blood, we can follow these steps:

### Step 1: Understand the forms of CO₂ in the blood
Carbon dioxide can exist in different forms in the blood. The primary forms include:
- Dissolved CO₂ in plasma
- Bicarbonate ions (HCO₃⁻)
- Carbamino compounds (bound to hemoglobin)

### Step 2: Identify the predominant form of CO₂
When CO₂ is released from body tissues, it primarily enters the bloodstream. The majority of CO₂ is converted into bicarbonate ions through a series of reactions involving carbonic acid (H₂CO₃).

### Step 3: The conversion process
In the red blood cells (RBCs), CO₂ reacts with water to form carbonic acid, which then dissociates into bicarbonate ions and hydrogen ions:
\[ \text{CO₂} + \text{H₂O} \leftrightarrow \text{H₂CO₃} \leftrightarrow \text{HCO₃⁻} + \text{H⁺} \]

### Step 4: Quantifying the forms of CO₂
Research indicates that about 70% of CO₂ is transported as bicarbonate ions in the plasma and red blood cells, while a smaller percentage is transported as dissolved CO₂ or as carbamino compounds.

### Step 5: Conclusion
Based on the above understanding, the bulk of carbon dioxide released from body tissues into the blood is present as bicarbonate in blood plasma and red blood cells.

### Final Answer
The correct answer is **bicarbonate in blood plasma and RBCs**.

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