Drive to breathe

Question 1

What does the dorsal respiratory group do (DRG)? (2)

Answer 1

Normal breathing
Inspiratory neurons (to diaphragm and ext. intercostals)

Question 2

What does the ventral respiratory group do (VRG)? (3)

Answer 2

Forced breathing (e.g. exercise)
Inspiratory & EXPIRATORY neurons
pre-Botzinger complex

Question 3

What is the pre-Botzinger complex and where is it located?

Answer 3

Respiratory rhythm generator –> sets basal respiratory rate

Located in VRG

Question 4

What does the apneustic centre do? (2)

Answer 4

Stimulates DRG

Increases intensity of inhalation (deep breaths)

Question 5

What does the pneumotaxic centre do? (3)

Answer 5

Inhibits apneustic centre
Promotes expiration
Shallow, frequent breaths (to prevent hyperventilation)

Question 6

What inhibits the apneustic centre?

Answer 6

Pneumotaxic centre

Question 7

Where are the DRG and VRG located?

Answer 7

Medulla

Question 8

Where are the apneustic and pneumotaxic centres located?

Answer 8

Pons

Question 9

What are slowly adapting stretch receptors (SASRs) activated by?

Answer 9

Lung distension

Question 10

During high activity, what do SASRS do?

Answer 10

Inhibit further inspiration to begin expiration

Question 11

What happens to SASRs if lung inflation is maintained?

Answer 11

They slowly adapt to low-frequency firing

Question 12

What are rapidly adapting stretch receptors (RASRs) activated by?

Answer 12

Lung distention and irritants

Question 13

During high activity, what do RASRs cause?

Answer 13

Bronchoconstriction

Question 14

Characteristic of RASR’s response to stimulation?

Answer 14

Produce brief burst of activity

Question 15

What are C fibres J receptors activated by?

Answer 15

Increase in interstitial fluid and thus pressure

Question 16

What do C fibres J receptors do? (4)

Answer 16

Rapid, shallow breaths
Bronchoconstriction
CV depression
Dry cough

Question 17

Where are peripheral chemoreceptors located?

Answer 17

Carotid bodies

Aortic bodies

Question 18

What do peripheral chemoreceptors respond to?

Answer 18

Decreased PaO2

Increased arterial [H+] due to increased CO2

Question 19

How do peripheral chemoreceptors respond on detection of hypoxia? (2)

Answer 19

Stimulate medullary inspiratory neurons

Increases ventilation

Question 20

Why aren’t peripheral chemoreceptors sensitive to small reductions of PaO2?

Answer 20

Begin firing when PaO2 is near 60mmHg as Hb is 90% saturated.
Increasing ventilation before this would have little increase in PaO2

Question 21

Why is there no peripheral chemoreceptor input in presence of CO?

Answer 21

PaO2 is unaffected

CO doesn’t affect amount of O2 dissolved in blood or oxygen-diffusion capacity of the lung

Question 22

Where are central chemoreceptors located?

Answer 22

Medulla oblongata

Question 23

What do central chemoreceptors respond to?

Answer 23

Increased [H+] of CSF

Very small increases in PaCO2

Question 24

How do central chemoreceptors respond to small increases in PaCO2? (2)

Answer 24

Stimulate medullary inspiratory neurons

Increases ventilation

Question 25

Why are central chemoreceptors more sensitive to small increases in PaCO2?

Answer 25

CO2 diffuses into CSF and contributes to CSF pH

Question 26

Why are changes in blood [H+] poorly reflected in the CSF?

Answer 26

BBB impermeable to H+

Question 27

What causes the drive to breathe?

Answer 27

Increased CO2 in blood, not necessarily the low O2

Question 28

What is hypoxia?

Answer 28

Deficiency of O2 at tissue level

Question 29

What the 4 common causes of hypoxia?

Answer 29

• Hypoventilation
• Diffusion impairment
• Shunting
• Ventilation-perfusion mismatch (most common cause)

Question 30

What is hypercapnia?

Answer 30

CO2 retention and increased PaCO2

Main drive to breathe!

Question 31

What happens in type 1 respiratory failure?

Answer 31

1 change: low pO2, normal/low PaCO2

Question 32

What happens in type 2 respiratory failure?

Answer 32

2 changes: low pO2, high PaCO2