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 and inspiration
 * Pneumotaxic center (in upper pons): regulates length of inhalation 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 primarily to pCO2 change, also acidosis)
 * Activation leads to hyperventilation within 20-30 s

Peripheral

 * Carotid and aortic bodies
 * Sensitive to
 * decreases in pO2 < 10-13 kPa (baroreceptors)
 * increases in pCO2 (baroreceptors)
 * decreases in pH (chemoceptors)
 * heat (thermoreceptors)
 * stimulation leads to hyperventilation

Mechanoreceptors

 * Lung stretch receptors (in smooth muscle of airways): 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

Defensive respiratory responses to irritants
Lungs are protected from irritants via several mechanisms:

Mechanical protection

 * vibrissae in the nasal cavity trap dust particles
 * mucociliary escalator in conducting airways moves mucus into pharynx

Immune protection

 * pulmonary alveolar macrophages
 * IgA antibodies in bronchial secretion

Herring-Breuer
Prevents excess inspiration or exhalation


 * 1) Pulmonary stretch receptors sense tension abnormality
 * 2) Signal is conducted via vagus nerve to medulla (inspiration regulation) or pontine center (expiration regulation)
 * 3) Appropriate inspiratory/expiratory reflex generated

Cough

 * 1) Irritation of airway receptors, pharynx, pleura, diaphragm, perichondrium, stomach, auditory canal or tympanic membrane
 * 2) Signal conducted via CNs V, IX, X and phrenic nerves to medulla
 * 3) CN X, phrenic nerve, and spinal motor nerve generate response of respiratory muscles:
 * 4) *small inspiration followed by forced expiration against closed glottis
 * 5) * pressures in thorax and abdomen build up
 * 6) * glottis is forced open
 * 7) air rushes out, loosens mucus and irritants (usually fine particles)

Sneeze

 * 1) Irritation of nasal mucosa or excess fluid in airway stimulates olfactory receptors or CN V endings
 * 2) Signal is conducted to medulla: nucleus solitarius and reticular formation
 * 3) CNs V, VII, IX, and X generate response of pharyngeal, tracheal, and respiratory muscles:
 * 4) * deep inspiration
 * 5) * pressures in thorax and abdomen rise, but pharynx constricts
 * 6) * air is forced through nose and mouth, facial and nasal muscles also constrict
 * 7) air rushes out, loosens mucus and irritants

Hiccup

 * 1) Abrupt intake of excess air (ex: via eating) stimulates sympathetic, phrenic, and vagus nerves (can also be stimulated by neural damage)
 * 2) Signal is conducted to midbrain
 * 3) Motor fibers of phrenic nerve and accessory nerves stimulate diaphragm and intercostal muscles
 * 4) Spasmotic contraction of diaphragm closes glottis