Control of Ventilation

Question 1

Which muscles need to be stimulated for ventilatory control

Answer 1

Skeletal muscles of inspiration

Question 2

Which nerves allows skeletal muscle stimulation for inspiration

Answer 2

Phrenic (to diaphragm) and intercostal nerves (to external intercostal muscles)

Question 3

Which parts of the brain are involved in respiration and what are they called

Answer 3

Pons and Medulla

Respiratory centres

Question 4

State 4 features of ventilatory control

Answer 4

It lies within ill defined centres located in the pons and medulla
Is normally subconscious
Can be subject to voluntary modulation
Is entirely dependent on signalling from the brain

Question 5

Where does a spinal cord injury have to occur to cause breathing to cease

Answer 5

Above origin of phernic nerve (C3-5)

Question 6

Name two functions of respiratory centres

Answer 6

1) To set an automatic rhythm of breathing by coordinating the firing of smooth and repetitive bursts of action potentials in the dorsal respiratory group (DRG) travel to inspiratory muscles
2) To adjust this rhythm in response to stimuli

Question 7

Which 4 things can modulate the respiratory centres

Answer 7

Emotion (through limbic system in the brain)
Voluntary over-ride (through higher centres in the brain)
Mechano-sensory input from the thorax (e.g. stretch reflex)
Chemical composition of the blood (PCO2, PO2 and pH) – detected by chemoreceptors

Question 8

Which of the 4 things which can modulate respiratory centers is the most important

Answer 8

The chemical composition of the blood (PCO2, PO2 and pH) – detected by chemoreceptors

Question 9

What is the DRG and VRG

Answer 9

DRG: Dorsal Respiratory Group of neurons
VRG: Ventral Respiratory Group of neurons

Question 10

What type of chemoreceptors are there

Answer 10

Central

Peripheral

Question 11

Where are central chemoreceptors found and what do they respond to

Answer 11

Medulla

Respond directly to H+ which directly reflects PCO2

Question 12

Where are peripheral chemoreceptors found and what do they respond to

Answer 12

Carotid and aortic bodies

Respond primarily to plasma [H+] and PO2 (less to PCO2)

Question 13

What is the primary and secondary ventilatory drive

Answer 13

Primary ventilatory drive - Central chemoreceptors

Secondary ventilatory drive - Peripheral

Question 14

What do central chemoreceptors detect

Answer 14

Changes in the [H+] in CSF around brain

Question 15

What do changes in the [H+] in CSF around brain cause

Answer 15

Reflex stimulation of ventilation following a rise in [H+] (driven by raised PCO2 = Hypercapnea)

Question 16

CO2 + H2O produces

Answer 16

H2CO3 (carbonic acid) which is converted to H+ and HCO3- (bicarbonate)

Question 17

How can ventilation be reflexly inhibited

Answer 17

By a decrease in arterial PCO2 which reduces CSF [H+] causing hyper ventilation

Question 18

What will central chemoreceptors not respond to

Answer 18

Direct changes in plasma [H+]

Question 19

What will an increase in arterial Pco2 cause

Answer 19

Causes CO2 to cross blood brain barrier

Feedback occurs through the respiratory centres to increase ventilation

Question 20

What do central chemoreceptors monitior

Answer 20

Pco2 indircetly in the CSF

Question 21

What does a decrease in arterial Pco2 do

Answer 21

Slows ventilation rate

Question 22

What do peripheral chemoreceptors detect

Answer 22

Changes in the arterial PO2 and [H+]

Question 23

What do peripheral chemoreceptors cause

Answer 23

reflex stimulation of ventilation following a significant fall in arterial PO2 or a rise in [H+]

Question 24

What do peripheral chemoreceptors respond to

Answer 24

Arterial PO2 not the oxygen content

Question 25

In regards to peripheral chemoreceptors what normmaly accompanies and increased [H+]

Answer 25

Rise in arterial PCO2

Question 26

What do changes in plasma pH cause

Answer 26

They alter ventilation through the peripheral chemoreceptor pathways

Question 27

What happens if plasma pH falls ([H+] increases)

Answer 27

Ventilation will be stimulated (acidosis)

Question 28

What happens if plasma pH increases ([H+] decreases)

Answer 28

Ventilation will be inhibited

E.g. vomiting (alkalosis)

Question 29

In what direction will the equation move when ventilation is increased

Answer 29

To the left to blow off CO2 and lower [H+]

Question 30

In what direction will the equation move when ventilation is decreased

Answer 30

To the right to retain CO2 and increase [H+]

Question 31

What do descending neural pathways from the cerebral cortex to the respiratory motor neurones allow

Answer 31

A large degree of voluntary control over breathing

Question 32

What can the descending neural pathways from the cerebral cortex to the respiratory motor neurones not overide

Answer 32

The involuntary stimuli such as arterial PCO2 or [H+]

Question 33

Name 3 other ways in which breathing can be controlled

Answer 33

Breath holding
Hyperventilation
Respiration is inhibited when swallowing to avoid aspiration of foods or fluids into the airways

Question 34

What does breathing in CO2 cause

Answer 34

Increases PaCO2 which impairs the partial pressure gradient which normally allows the removal of CO2 from pulmonary artery
CO2 remains in blood causing the partial pressure gradient at the periphery which pulls CO2 out of cells to be lost causing CO2 to build up in the cells

Question 35

What do barbiturates and opioids do

Answer 35

Depress the respiratory centre (overdose normally results in death because of respiratory failure)

Question 36

What do gaseous anaesthetic agents do

Answer 36

Increase respiratory rate but decrease TV so decrease AV

Question 37

What does nitrous oxide (commn sedative) do

Answer 37

Blunts peripheral chemoreceptor response to falling PaO2

Question 38

Why is swallowing followed by expiration

Answer 38

So that any particles are dislodged outwards from the region of the glottis