Drive to breathe Flashcards
What does the dorsal respiratory group do (DRG)? (2)
Normal breathing Inspiratory neurons (to diaphragm and ext. intercostals)
What does the ventral respiratory group do (VRG)? (3)
Forced breathing (e.g. exercise)
Inspiratory & EXPIRATORY neurons
pre-Botzinger complex
What is the pre-Botzinger complex and where is it located?
Respiratory rhythm generator –> sets basal respiratory rate
Located in VRG
What does the apneustic centre do? (2)
Stimulates DRG
Increases intensity of inhalation (deep breaths)
What does the pneumotaxic centre do? (3)
Inhibits apneustic centre
Promotes expiration
Shallow, frequent breaths (to prevent hyperventilation)
What inhibits the apneustic centre?
Pneumotaxic centre
Where are the DRG and VRG located?
Medulla
Where are the apneustic and pneumotaxic centres located?
Pons
What are slowly adapting stretch receptors (SASRs) activated by?
Lung distension
During high activity, what do SASRS do?
Inhibit further inspiration to begin expiration
What happens to SASRs if lung inflation is maintained?
They slowly adapt to low-frequency firing
What are rapidly adapting stretch receptors (RASRs) activated by?
Lung distention and irritants
During high activity, what do RASRs cause?
Bronchoconstriction
Characteristic of RASR’s response to stimulation?
Produce brief burst of activity
What are C fibres J receptors activated by?
Increase in interstitial fluid and thus pressure
What do C fibres J receptors do? (4)
Rapid, shallow breaths
Bronchoconstriction
CV depression
Dry cough
Where are peripheral chemoreceptors located?
Carotid bodies
Aortic bodies
What do peripheral chemoreceptors respond to?
Decreased PaO2
Increased arterial [H+] due to increased CO2
How do peripheral chemoreceptors respond on detection of hypoxia? (2)
Stimulate medullary inspiratory neurons
Increases ventilation
Why aren’t peripheral chemoreceptors sensitive to small reductions of PaO2?
Begin firing when PaO2 is near 60mmHg as Hb is 90% saturated.
Increasing ventilation before this would have little increase in PaO2
Why is there no peripheral chemoreceptor input in presence of CO?
PaO2 is unaffected
CO doesn’t affect amount of O2 dissolved in blood or oxygen-diffusion capacity of the lung
Where are central chemoreceptors located?
Medulla oblongata
What do central chemoreceptors respond to?
Increased [H+] of CSF
Very small increases in PaCO2
How do central chemoreceptors respond to small increases in PaCO2? (2)
Stimulate medullary inspiratory neurons
Increases ventilation
Why are central chemoreceptors more sensitive to small increases in PaCO2?
CO2 diffuses into CSF and contributes to CSF pH
Why are changes in blood [H+] poorly reflected in the CSF?
BBB impermeable to H+
What causes the drive to breathe?
Increased CO2 in blood, not necessarily the low O2
What is hypoxia?
Deficiency of O2 at tissue level
What the 4 common causes of hypoxia?
- Hypoventilation
- Diffusion impairment
- Shunting
- Ventilation-perfusion mismatch (most common cause)
What is hypercapnia?
CO2 retention and increased PaCO2
Main drive to breathe!
What happens in type 1 respiratory failure?
1 change: low pO2, normal/low PaCO2
What happens in type 2 respiratory failure?
2 changes: low pO2, high PaCO2
