Describe the control of alveolar ventilation.

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College Answer

The most comprehensive answers were those structured as sensor-controller-effector with an 
explanation of each part and how homeostasis was maintained. Insufficient detail was generally 
provided as to how central and peripheral chemoreceptors were stimulated. A description of 
central control was required, rather than listing nuclei or areas.
Many failed to address all three components of a control question and focused primarily on the 
sensors. Many answers were just too brief and did not present enough information to 
demonstrate understanding

Discussion

This is a question which Nunn's takes twenty pages to answer, so condensing it requires a bit of preparation. Ideally, the exam candidate will have a prefabricated answer stored in their cheek pouch, ready to regurgitate.  Tabulated answers are almost always the best, and so here a series of tables  which hopefully "present enough information to demonstrate understanding".

Sensor Organs involved in the Control of Respiratory Function
Sensor Stimulus Afferent nerve

Carotid body glomus
(Type I cells) - sited at the bifurcation of the common carotid

  • PaO2
  • PaCO2
  • pH
  • Temperature
  • Glucose (hypoglycaemia)
Glossopharyngeal
Aortic glomus cells - in the aortic arch, subclavian arteries and pulmonary trunk
  • PaO2
  • Changes in O2 delivery (anaemia, carboxyhaemoglobin, hypotension)
  • PaCO2
Aortic nerve
(branch of the vagus)
Central chemoreceptors
  • pH
-
Mechanoreceptors in bronchial and lung tissue
  • Inflation and deflation (i.e. Hering-Breuer reflex)
Vagus
Respiratory Control Centres
Controller Role Efferents and effectors
Nucleus retroambigualis Expiratory function

Upper motor neuron axons to contralateral expiratory muscles

Nucleus paraambigualis Inspiratory function

Upper motor neuron axons to contralateral inspiratory muscles

Nucleus ambiguous Airway dilator function

Vagus nerve: to (larynx, pharynx and muscularis uvulae)

Glossopharyngeus muscle to stylopharyngeus muscle

Pre-Bötzinger complex Respiratory pacemaker ("central pattern generator") Interneurons connecting to other respiratory control regions
Bötzinger complex Expiratory function

Inhibitory interneurons to phrenic motor neurons and other respiratory control regions

Pontine respiratory group

Integrates descending control of respiration from the CNS

Interneurons connecting to other respiratory control regions
Cerebral cortex Volitional and behavioural  respiratory control Pontine respiratory group

References

References

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