Chloride shift occurs in respond to

Options

A. `H^(+)`
B. `K^(+)`
C. `Na^(+)`
D. `HCO_(3)`

Answer

**Step-by-Step Solution:**

1. **Understanding Chloride Shift**: The chloride shift refers to the process that occurs in red blood cells (RBCs) during the transport of carbon dioxide (CO2) from tissues to the lungs. It involves the exchange of bicarbonate ions (HCO3-) and chloride ions (Cl-).

2. **Role of Carbon Dioxide**: When CO2 enters the RBCs, it reacts with water to form carbonic acid (H2CO3), which quickly dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+). This reaction is facilitated by the enzyme carbonic anhydrase.

3. **Movement of Bicarbonate Ions**: The bicarbonate ions produced in the RBCs are then transported out of the cells into the plasma. This movement is crucial for maintaining the acid-base balance in the blood.

4. **Chloride Ion Movement**: To maintain electrical neutrality and balance the charge, chloride ions from the plasma enter the RBCs in exchange for the bicarbonate ions that are leaving. This exchange is what is referred to as the chloride shift.

5. **Conclusion**: The chloride shift occurs specifically in response to the movement of bicarbonate ions out of the RBCs into the plasma. Therefore, the correct answer to the question is the bicarbonate ion.

**Final Answer**: The chloride shift occurs in response to the bicarbonate ion (Option 4).

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