The respiratory mechanism is controlled by the :

Options

A. parasympathetic nervous system
B. sympathetic nervous system
C. central nervous system
D. peripheral nervous system

Explanation

### Step-by-Step Solution:

1. **Understanding the Respiratory Mechanism**: The respiratory mechanism is primarily responsible for the exchange of gases, which involves taking in oxygen and expelling carbon dioxide. This process is crucial for maintaining the body's metabolic functions.

2. **Role of the Lungs**: The lungs are the main organs involved in this process. They contain tiny air sacs called alveoli, where the actual gas exchange occurs. However, before gas exchange can take place, air must be conducted to the alveoli.

3. **Breathing Process**: The act of breathing (or pulmonary ventilation) is how air is moved in and out of the lungs. This process is not constant and can vary based on different physiological needs.

4. **Regulation of Breathing**: The rate and depth of breathing are regulated by the respiratory rhythm center located in the brain. Specifically, this center is found in the medulla oblongata, which is part of the central nervous system (CNS).

5. **Response to Carbon Dioxide Levels**: The respiratory rhythm center monitors the levels of carbon dioxide (CO2) and hydrogen ions (H+) in the blood. If these levels rise, indicating that the body needs to expel more CO2, the center will adjust the breathing rate accordingly.

6. **Conclusion**: Since the respiratory rhythm center is located in the medulla oblongata of the brain, we can conclude that the respiratory mechanism is controlled by the central nervous system.

### Final Answer:
The respiratory mechanism is controlled by the **medulla oblongata** in the brain, which is part of the central nervous system.

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