Control of Ventilation Flashcards
What are the muscles of inspiration?
The diaphragm and external intercostals
What are the expiration muscles?
Inner intercostal and abdominals (usually not required as PASSIVE)
What are the respiratory centre in the brain?
Signals sent from Medulla and Pons
What is the role of respiratory centres?
Medulla and Pons - set autonomic rhythm of breathing through co-ordinating the firing of smooth and repetitive bursts of APs in DRG - travel to inspiratory muscles
Will adjust the rhythm in response to stimuli
What is the ventral respiratory group (VRG)?
Nerves that innervate the muscles of expiration and innervates the larynx, pharynx (keeps airways patent) and tongue
What can modulate rhythm in respiratory centres?
- Emotion
- Voluntary over-side
- Mechano-sensory input from thorax (stretch reflex) - fire when thoracic cavity too full and send neg. feedback to prevent over inflation
- Chemoreceptors detect chemical composition in blood (PCO2, PO2, pH) - centres initiate change in breathing pattern to restore original pH
Describe central chemoreceptors
Located in medulla
Activated by changes in [H+] in CSF around brain (directly reflects PCO2)
Primary ventilatory drive
Cause reflex stim. of breathing after rise in [H+] (driven by raised PCO2 - hypercapnia) and rise versa (decrease in hyperventilation)
Describe mechanism of central chemoreceptors
- When arterial PCO2 increases, CO2 crosses blood brain barrier
- Central chemoreceptors monitor PCO2 indirectly in CSF
- Once it has crossed, it converts into HCO2 and H+ - and receptors respond to H+
- Feedback via resp. centres INCREASES ventilation in response to INCREASED arterial PCO2 (decreased PCO2 = decreased ventilation)
Describe peripheral chemoreceptors
- Located in the carotid and aortic bodies
- Responds to plasma [H+] and PO2 (made through processes and not just CO2)
- SECOND ventilatory drive
Cause reflex stim. of ventilation in response to decrease in PO2 or rise in [H+]
What is the effect of pH on ventilation, stimulated by peripheral chemoreceptors?
Decrease in pH ([h+] increase - acidosis) ventilation stimulated
Increase in pH ([H+] falls - alkalosis) ventilated inhibited
Drug effect on resp. centres
- Barbiturates and opioids depress resp. centre - overdoes can lead to death due to resp. failure
- Nitrous oxide (light anaesthetic) blunts peripheral chemoreceptor response to falling PaO2 - problem in lung disease where patient on hypoxic drive
Which nerves innervate the muscle of inspiration?
Phrenic to the diaphragm
Intercostal nerves to the external IC muscles
What is the Dorsal Respiratory Group (DRG)?
Nerves that innervate the inspiratory muscles via the phrenic and vagus nerve
What is the most significant input to the Respiratory Centres?
Chemoreceptor input
What is the general action of chemoreceptors
Maintains blood gas homeostasis
CO2 is main stimulus for change
