The respiratory centre in medulla is sensitive to

Options

A. high `Co_(2)` concentration
B. low `O_(2)` concentration
C. high `O_(2)` concentration
D. all of the above

Answer

### Step-by-Step Solution

1. **Understanding the Respiratory Center**: The respiratory center is located in the medulla oblongata of the brain. It plays a crucial role in regulating the process of respiration.

2. **Function of the Respiratory Center**: The primary function of the respiratory center is to control the rate and depth of breathing. It responds to changes in the levels of gases in the blood, particularly carbon dioxide (CO2) and oxygen (O2).

3. **Sensitivity to Carbon Dioxide**: The medulla oblongata is particularly sensitive to the concentration of carbon dioxide in the blood. When the levels of CO2 rise, it indicates that the body is producing more acid (due to the formation of carbonic acid), which lowers the pH of the blood.

4. **Response to High CO2 Levels**: When there is a high concentration of CO2, the medulla oblongata triggers an increase in the respiratory rate. This is because the body needs to expel more CO2 and take in more oxygen to restore balance.

5. **Considering Other Options**: While the medulla also responds to low oxygen levels, the primary stimulus for the respiratory center is the concentration of CO2. High oxygen levels do not stimulate the respiratory center.

6. **Conclusion**: Therefore, the respiratory center in the medulla is most sensitive to high carbon dioxide concentration.

### Final Answer
The respiratory center in the medulla is sensitive to **high carbon dioxide concentration**.

---