Control of breathing

Question 1

Where is the respiratory centre?

Answer 1

Pons and Medulla (in brainstem)

Question 2

What would happen to respiration if the brainstem was sectioned above the Pons?

Answer 2

Respiration could continue essentially normally

Question 3

What would happen to respiration if the brainstem was sectioned below the Medulla?

Answer 3

Respiration would cease as brainstem would be disconnected from the spinal cord

Question 4

Where are inspiratory and expiratory neurones found?

Answer 4

Inspiratory neurones are found in both the dorsal and ventral respiratory groups.

Expiratory neurones are found in the ventral group only.

Question 5

What are the 3 components of the feedback cycle?

Answer 5

1. Central controller (pons, medulla, other parts of brain)
2. Effectors (receive output from central controller and send messages to sensors)
3. Sensors (include chemoreceptors, lungs and other receptors and send input back to the central controller)

Question 6

Where are central chemoreceptors found?

Answer 6

Medullary surface of brainstem

Question 7

What is the function of central chemoreceptors?

Answer 7

Sense composition (pH) of CSF:

Low pH (caused by increased pCO2) leads to increased ventilation rate 
High pH (caused by increased HCO3-) leads to decreased ventilation rate

Question 8

What are the physiological effects of hypoventilation?

Answer 8

Hypoventilation causes fall in PaO2 and rise in PaCO2

Question 9

What is the function of peripheral chemoreceptors?

Answer 9

Stimulate response to hypoxia when detected by sensors in carotid bodies.

Impulse sent to respiratory centre via the glossopharyngeal nerve.

Leads to increased ventilation rate

Question 10

What is the physiological response to hypercapnia?

Answer 10

Buffer systems (i.e. increased bicarbonate production)

Question 11

What is the physiological response to hypocapnia?

Answer 11

Decreased ventilation

Question 12

Define ‘base excess’

Answer 12

The amount of strong acid that must be added (or removed) for each litre of fully oxygenated blood to return the pH to normal (7.4) at a temperature of 37 degrees and a pCO2 of 5.3kPa

Question 13

How is an arterial blood sample analysed?

Answer 13

1. Identify hypoxia (PaO2 of less than 8.3kPa)
2. Identify direction of pH change (acidosis or alkalosis )
3. Identify magnitude of pH change
4. Identify compensation

[Nb. other things to identify = serum lactate, base excess]

Question 14

What are the 5 causes of metabolic acidosis?

Answer 14

Lactic acidosis
Ketoacidosis
Acute renal failure
Excessive loss of bicarbonate 
Other causes e.g. poisons (aspirin, methanol etc.)