How is alveolar ventilation regulated?
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.
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 | Stimulus | Afferent nerve |
|
Carotid body glomus |
|
Glossopharyngeal |
| Aortic glomus cells - in the aortic arch, subclavian arteries and pulmonary trunk |
|
Aortic nerve (branch of the vagus) |
| Central chemoreceptors |
|
- |
| Mechanoreceptors in bronchial and lung tissue |
|
Vagus |
| 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 |
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