Hering-Breuer inflation reflex is mediated by which receptor type and pathway, and what is its primary physiological role in adult humans?
- A J receptors (juxtacapillary receptors) in the alveolar wall via C fibres; triggers rapid shallow breathing in response to oedema
- B Rapidly adapting irritant receptors in the bronchial epithelium via myelinated vagal fibres; maintains functional residual capacity
- C Slowly adapting pulmonary stretch receptors (SARs) in airway smooth muscle via vagal afferents to the apneustic centre; limits excessive tidal volume, mainly active above 1 litre ✓
- D Central chemoreceptors in the ventrolateral medulla; directly modulates breath termination based on CO2 level
Explanation
The Hering-Breuer inflation reflex is triggered by slowly adapting pulmonary stretch receptors (SARs) located in airway smooth muscle. Afferents travel via the vagus to the pontine and medullary respiratory centres, inhibiting inspiration and promoting exhalation (switch-off mechanism). In adult humans, this reflex is relatively weak at normal tidal volumes and becomes physiologically significant only at tidal volumes above approximately 1 litre. It is more important in newborns and anaesthetised states. J receptors mediate dyspnoea/oedema responses; irritant receptors mediate cough and bronchoconstriction.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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