Aortic and carotid chemoreceptors respond the quickest when PO2 levels fall below 60 mmHg.

Question

BlackTom AI · Accepted Answer

Peripheral (aortic and carotid) chemoreceptors are most sensitive to hypoxemia and markedly increase their firing when arterial PO2 falls below about 60 mmHg.

1) Relevant knowledge points and concepts
- Peripheral chemoreceptors (carotid bodies primarily, aortic bodies to a lesser extent) detect arterial PO2, PaCO2, and pH; they are the principal sensors for acute hypoxia.
- Central chemoreceptors (medulla) respond mainly to changes in PaCO2 via CSF pH, not directly to O2.
- The oxyhemoglobin dissociation curve becomes steep below a PaO2 of ~60 mmHg, so small drops in PO2 produce large drops in O2 saturation — a stimulus for increased chemoreceptor activity.

2) Step-by-step reasoning
- At normal arterial PO2 (~95–100 mmHg) carotid/aortic chemoreceptor firing is low.
- As PO2 decreases into the steep portion of the dissociation curve, receptor activity rises sharply.
- Clinically and experimentally, a threshold around 60 mmHg is recognized: below this, ventilatory drive from peripheral chemoreceptors increases significantly.

3) Calculations / intermediate values
- Typical values: PaO2 ≈ 100 mmHg → SaO2 ≈ 97–100%.
- PaO2 ≈ 60 mmHg → SaO2 ≈ 90%.
- The drop from near-100% to ~90% saturation occurs across this range, demonstrating why chemoreceptors respond strongly once PO2 < 60 mmHg.

4) Why the correct answer is correct
- Because peripheral chemoreceptors are tuned to detect dangerous hypoxemia and the steep part of the O2 dissociation curve begins near PaO2 = 60 mmHg, they “respond the quickest” when PO2 falls below that value, triggering increased ventilation.

5) Why the other option is incorrect
- “False” would imply chemoreceptors do not preferentially respond below 60 mmHg; this contradicts physiological evidence and the known threshold for peripheral chemoreceptor activation. Central chemoreceptors also do not substitute because they sense CO2/pH, not PO2.

Conclusion: The statement is True, matching the provided answer.

Aortic and carotid chemoreceptors respond the quickest when PO2 levels fall below 60 mmHg.判断题

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