The respiratory centre in the brain is stimulated by

Options

A. carbon dioxide content in venous blood
B. carbon dioxide content in artierial blood
C. oxygen content in venous blood
D. oxygen content in artierial blood

Answer

### Step-by-Step Solution

1. **Identify the Respiratory Center**: The respiratory center in the brain is primarily located in the medulla oblongata and pons. These areas are responsible for controlling the process of respiration.

2. **Stimuli for the Respiratory Center**: The respiratory center is stimulated mainly by the levels of carbon dioxide (CO2) in the arterial blood. An increase in CO2 concentration is a key factor that triggers the respiratory center.

3. **Mechanism of Detection**: The body has specialized receptors located in the carotid arteries that detect changes in CO2 levels. When CO2 levels rise, these receptors send signals to the respiratory center.

4. **Effect of CO2 on pH**: An increase in CO2 concentration leads to a decrease in blood pH, making the blood more acidic. This change in pH is another signal that stimulates the respiratory center.

5. **Response of the Respiratory Center**: In response to high CO2 levels or low oxygen levels (O2), the respiratory center increases the rate and depth of breathing. This helps to expel excess CO2 and increase oxygen intake.

6. **Conclusion**: Thus, the primary stimulus for the respiratory center in the brain is the concentration of carbon dioxide in the arterial blood.