`CO_2` dissociates from carbaminohaemoglobin in the alveoli when

Options

A. `pCO_2` is high and `pO_2` is low
B. `pO_2` is high and `pCO_2` is low
C. `pCO_2 and pO_2` are equal
D. `pCO_2` is high and `pO_2` is low with lesser

Answer

To solve the question regarding the dissociation of CO2 from carbaminohemoglobin in the alveoli, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Carbaminohemoglobin**:
- Carbaminohemoglobin is a form of hemoglobin that is bound to carbon dioxide (CO2). It plays a crucial role in transporting CO2 from the tissues to the lungs.

2. **Location of Dissociation**:
- The dissociation of CO2 from carbaminohemoglobin primarily occurs in the alveoli of the lungs, where gas exchange takes place.

3. **Role of Oxygen Concentration**:
- In the alveoli, the concentration of oxygen (O2) is relatively high due to inhalation. This high concentration of O2 influences the behavior of hemoglobin.

4. **Partial Pressure Dynamics**:
- The partial pressure of oxygen (PO2) in the alveoli is high, which leads to a decrease in the partial pressure of carbon dioxide (PCO2) in the blood. This difference in partial pressures drives the dissociation of CO2 from carbaminohemoglobin.

5. **Mechanism of Dissociation**:
- When the PO2 is high, hemoglobin has a higher affinity for oxygen and a lower affinity for carbon dioxide. Therefore, CO2 is released from carbaminohemoglobin into the alveoli.

6. **Conclusion**:
- Thus, CO2 dissociates from carbaminohemoglobin in the alveoli when the partial pressure of oxygen is high and the partial pressure of carbon dioxide is low.

### Final Answer:
CO2 dissociates from carbaminohemoglobin in the alveoli when the partial pressure of oxygen (PO2) is high and the partial pressure of carbon dioxide (PCO2) is low.

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