How is alveolar ventilation regulated?

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College Answer

This is a core topic (syllabus Level 1) and a high level of understanding was expected. Overall 
candidates failed to demonstrate sufficient depth and breadth in their knowledge. A 
structured response considering the three basic elements underpinning the control of 
alveolar ventilation (the Sensors, Central integration and control and the Effectors) was core 
material. A detailed description of each was expected.

Discussion

This question is essentially identical to Question 13 from the second paper of 2015 and Question 1 from the first paper of 2015, except the examiner comments this time were much more cranky. 

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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