Hering-Breuer Receptors Activation

Hering-Breuer receptors are activated when lung volume becomes ______ times of tidal volume:

Correct Answer: 3

The Hering-Breuer inflation reflex is activated when lung volume becomes approximately 3 times the tidal volume (i.e., roughly 3 × 500 ml = ~1500 ml in humans).

Hering-Breuer Reflex

• Pulmonary stretch receptors (slowly adapting receptors — SARs) are located in the smooth muscle of airways.
• When lungs are over-inflated (volume reaches ~3× tidal volume), these receptors are activated → send signals via the vagus nerve → inhibit the inspiratory center (DRG in medulla) → inspiration stops, expiration begins.
• This prevents over-distension of the lungs during deep or forced breathing.
• At normal tidal volumes, this reflex is relatively inactive in adult humans/animals during quiet breathing. It is more active in neonates and smaller animals.

Clinical Significance

• Vagotomy (cutting vagus nerve) → prolonged, deep inspirations (apneustic breathing) because Hering-Breuer reflex is abolished.
• The reflex is more prominent in animals with high respiratory rates (small animals, neonates, birds).