Question
In which of the following conditions are peripheral chemoreceptors most sensitive?
| A. |
Hypoxia |
| B. |
Hypercapnia |
| C. |
Alkalosis |
| D. |
Acidosis |
Show Answer
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Correct Answer � A Explanation |
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Peripheral Chemoreceptors
Peripheral chemoreceptors, located in the carotid bodies and aortic bodies, monitor changes in the arterial blood and primarily respond to:
Decreased oxygen levels (hypoxia):
- Peripheral chemoreceptors are most sensitive to a fall in arterial PO₂ (<60 mmHg).
- Hypoxia is the primary stimulus, especially when oxygen levels drop significantly.
- Mechanism: Decreased PO₂ leads to chemoreceptor activation, which increases afferent signaling to the respiratory center, stimulating ventilation.
Increased carbon dioxide levels:
- Hypercapnia (elevated CO₂ levels) also stimulates peripheral chemoreceptors, but it is primarily sensed by central chemoreceptors in the medulla.
- Peripheral chemoreceptors respond more robustly to hypoxia than hypercapnia.
Alkalosis (increased blood pH) decreases the activity of peripheral chemoreceptors, as it is not a strong stimulus for them.
Acidosis stimulates peripheral chemoreceptors, especially when associated with increased arterial CO₂ levels (respiratory acidosis).However, this response is secondary to hypoxia in terms of sensitivity.
Key Points About Peripheral Chemoreceptors
Primary Function: Detect decreases in arterial oxygen tension (PO₂).
Threshold: Activated strongly when arterial PO₂ falls below 60 mmHg.
Other Roles: Secondary response to hypercapnia and acidosis.
Clinical Correlation: Hypoxia-driven stimulation of peripheral chemoreceptors is crucial in conditions like chronic obstructive pulmonary disease (COPD), where oxygen levels are chronically low.