which of the following will cause a left shift in oxyhaemoglobin dissociation curve?

Options

A. high pCO_20
B. high H^+ concentration
C. high pH
D. low pH

Answer

To determine which factor causes a left shift in the oxyhemoglobin dissociation curve, we need to understand the conditions that influence this curve. The oxyhemoglobin dissociation curve illustrates how readily hemoglobin binds to and releases oxygen under varying conditions.

### Step-by-Step Solution:

1. **Understanding the Oxyhemoglobin Dissociation Curve**:
- The curve represents the relationship between the partial pressure of oxygen (pO2) and the percentage saturation of hemoglobin with oxygen. A left shift indicates that hemoglobin has a higher affinity for oxygen, meaning it binds oxygen more readily.

2. **Factors Influencing the Shift**:
- A left shift in the curve can occur due to several physiological changes:
- **Decreased pCO2 (partial pressure of carbon dioxide)**: Lower levels of carbon dioxide promote hemoglobin's affinity for oxygen.
- **Increased pH (alkalosis)**: A higher pH means fewer hydrogen ions (H+), which also increases hemoglobin's affinity for oxygen.
- **Lower temperature**: A decrease in temperature enhances oxygen binding to hemoglobin.

3. **Analyzing the Options**:
- **High pCO2**: This would cause a right shift, not a left shift, as increased carbon dioxide decreases hemoglobin's affinity for oxygen.
- **High H+ concentration**: This also leads to a right shift since more hydrogen ions lower the affinity for oxygen.
- **High pH**: This condition indicates fewer hydrogen ions and thus a left shift in the curve, meaning hemoglobin binds oxygen more tightly.

4. **Conclusion**:
- The factor that causes a left shift in the oxyhemoglobin dissociation curve is **high pH**.

### Final Answer:
The correct answer is **high pH**.