Which of the following chemoreceptors is responsible for detecting changes in arterial PaCO₂ and pH, and is located on the ventrolateral surface of the medulla?

Explanation

## Central Chemoreceptors: Location and Function **Key Point:** Central chemoreceptors are located on the ventrolateral surface of the medulla, bathed in cerebrospinal fluid (CSF). They are the primary sensors of arterial PaCO₂ and pH changes. ### Mechanism of Action Central chemoreceptors respond to: 1. **Increased PaCO₂** → CO₂ diffuses across the blood-brain barrier and forms H⁺ ions in the CSF 2. **Decreased pH** → Direct stimulation of chemoreceptor neurons 3. These changes trigger increased ventilation to restore normal PaCO₂ and pH ### Comparison with Peripheral Chemoreceptors | Feature | Central Chemoreceptors | Peripheral Chemoreceptors | |---------|------------------------|---------------------------| | Location | Ventrolateral medulla | Carotid and aortic bodies | | Primary stimulus | PaCO₂ and pH | PaO₂ (< 60 mmHg), PaCO₂, pH | | Response time | Slower (CSF diffusion) | Rapid (direct blood contact) | | Importance | 70-80% of ventilatory response to CO₂ | Hypoxia detection | **High-Yield:** Central chemoreceptors are more sensitive to chronic CO₂ changes because CO₂ readily crosses the blood-brain barrier, whereas H⁺ ions do not. This is why CSF pH becomes the effective stimulus over time. **Clinical Pearl:** In chronic hypercapnia (e.g., COPD), central chemoreceptors become desensitized to elevated CO₂, and the patient becomes dependent on hypoxia (via peripheral chemoreceptors) to drive ventilation. This is why supplemental O₂ must be given cautiously in these patients.