Regulation of ventilation

CNS regulation
Ventilation is regulated by several groups of neurons in the brainstem:


 * Medullary respiratory center (in reticular formation)
 * Dorsal respiratory group: inspiration and breathing rate
 * Ventral respiratory group: active expiration
 * Pneumotaxic center (n upper pons): inspiratory volume and breathing rate via inhibition

Several chemoreceptors and mechanoreceptors are important in providing sensory input to regulatory groups in the CNS.

Central

 * In medulla
 * Sensitive to pH changes of CSF (due to either pCO2 change or acidosis)
 * Activation leads to hyperventilation within 20-30 s

Peripheral

 * Carotid and aortic bodies
 * Sensitive to
 * decreases in pO2 < 10-13 kPa
 * increases in pCO2
 * decreases in pH
 * stimulation leads to hyperventilation

Mechanoreceptors

 * Lung stretch receptors (in smooth muscle of airways): decrease respiratory rate – Hering-Breuer reflex
 * Irritant receptors (between airway epithelial cells): stimulated by noxious particles
 * Juxtacapillary receptors (in alveolar walls by capillaries): stimulated by engorgement of capillaries, leading to tachypnea
 * Joint and muscle receptors: activated to stimulate early breathing during exercise

Cough
Irritation of lower airway receptors → small inspiration followed by forced expiration against closed glottis → pressures in thorax and abdomen rise → glottis is forced open → air rushes out, loosens mucus and foreign particles. Irritation of laryngeal receptors does not lead to inspiration.

Sneeze
Irritation of nasal receptors → deep inspiration → pressures in thorax and abdomen rise but pharynx constricts → air is forced through nose and mouth, facial and nasal muscles also constrict → mucus and foreign bodies are loosened.