Control of ventilation

Question 1

Main features of the respiratory centres?

Answer 1

• They maintain a rhythmic rate of respiration
• They are situated in the pons and the medulla
• They are stimulate the inspiratory muscles through action potential sent through the dorsal region group of nerves

Question 2

Stimuli which trigger the respiratory centres

Answer 2

Emotion-via the lymbic system
Voluntary over-ride
Mechano-receptors in the thorax
Chemo-receptors which respond to change in the chemical composition of the blood

Question 3

Central chemoreceptors

Answer 3

Found in the medulla
Respond to change in PCO2
PCO2 and not H+ can cross the BBB.
Chemoreceptors indirectly control the concentration of CO2 in the blood.
When it increases there is an increase in the conc. of H+
This triggers the respiratory centres to increase ventilation.

Question 4

Peripheral chemoreceptors

Answer 4

The carotid and aortic bodies.
Respond to changes in P02 and H+.
They respond to partial pressure of 02 not arterial content.

Question 5

Other mechanisms of ventilation control

Answer 5

-Hyperventilation
-Holding of breath
-Descending neural pathways found from the cerebral cortex to the motor neurones of the inspiratory muscles.
- Swallowing of food-inhibition of respiration to prevent food particles entering the airways
-DRUGS:
= NO- prevents the peripheral chemoreceptors responding to changes in PaO2
= Opiods and barbiturates- depress the respiratory centres
= Gaseos anaestetics- increase the respiratory rate but decrease the Tidal volume so therefore decrease the Alveolar ventilation

Question 6

DRG and VRG

Answer 6

Dorsal region group- output to the inspiratory muscles via the phrenic nerve and intercostal nerves
Ventral region group- output to the tongue, larynx, Pharnyx and expiratory muscles

Question 7

Which nerves are involved?

Answer 7

The phrenic and intercostal nerves

Question 8

How does the peripheral chemoreceptor mechanism work?

Answer 8

• Decrease in P02- makes the K02 receptors less sensitive.
• K02 channels close which leads to a decrease in K inside the cell
• This leads to depolarisation which causes dopamine to be released from the cell by exocytosis
• The dopamine binds to receptors of afferent sensory neurones which causes an impulse to be sent to the medullary centres

Question 9

What is hypoxic drive and when does it present?

Answer 9

Oxygen chemoreceptors and used instead on co2 ones in the control of ventilation
Presents in chronic lung disease patients who are administered NO

Question 10

Dorsal region group of nerve supplies?

Answer 10

The inspiratory muscles

Question 11

Ventral region group of nerves supplies?

Answer 11

Tongue, pharynx, larynx, Expiratory muscles

Question 12

Hypercapnia

Answer 12

Increased levels of Co2 in arterial blood

Question 13

Indirect control of breathing tends to be through?

Answer 13

The central chemoreceptors

Question 14

Direct control of breathing tends to be through?

Answer 14

The peripheral chemoreceptors

Question 15

Different levels of distress based on Pc02 and P02 levels?

Answer 15

very distressed
high PCO2 
Normal 02
Mild discomfort
Normal PC02
Low P02