The 'Hering-Breuer reflex' is primarily a response to:

 # The 'Hering-Breuer reflex' is primarily a response to:

 A. High levels of CO2

 B. Over-inflation of the lungs

 C. Low levels of O2

D. Irritants in the airway

The correct answer is B. Over-inflation of the lungs.

The Hering-Breuer reflex is a protective mechanism that prevents over-inflation of the lungs. It is triggered by stretch receptors in the airways and lungs that detect excessive lung expansion during inspiration. When activated, the reflex sends signals via the vagus nerve to the respiratory center in the brain, inhibiting further inspiration and promoting expiration to prevent lung damage.

• A. High levels of CO2: CO2 levels primarily stimulate the respiratory center through chemoreceptors, not the Hering-Breuer reflex.
• C. Low levels of O2: Low oxygen levels are detected by peripheral chemoreceptors, which stimulate breathing but are not related to the Hering-Breuer reflex.
• D. Irritants in the airway: Airway irritants trigger reflexes like coughing or bronchoconstriction, not the Hering-Breuer reflex.