Control of Ventilation Flashcards
Which muscles need to be stimulated for ventilatory control
Skeletal muscles of inspiration
Which nerves allows skeletal muscle stimulation for inspiration
Phrenic (to diaphragm) and intercostal nerves (to external intercostal muscles)
Which parts of the brain are involved in respiration and what are they called
Pons and Medulla
Respiratory centres
State 4 features of ventilatory control
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
Where does a spinal cord injury have to occur to cause breathing to cease
Above origin of phernic nerve (C3-5)
Name two functions of respiratory centres
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
Which 4 things can modulate the respiratory centres
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
Which of the 4 things which can modulate respiratory centers is the most important
The chemical composition of the blood (PCO2, PO2 and pH) – detected by chemoreceptors
What is the DRG and VRG
DRG: Dorsal Respiratory Group of neurons
VRG: Ventral Respiratory Group of neurons
What type of chemoreceptors are there
Central
Peripheral
Where are central chemoreceptors found and what do they respond to
Medulla
Respond directly to H+ which directly reflects PCO2
Where are peripheral chemoreceptors found and what do they respond to
Carotid and aortic bodies
Respond primarily to plasma [H+] and PO2 (less to PCO2)
What is the primary and secondary ventilatory drive
Primary ventilatory drive - Central chemoreceptors
Secondary ventilatory drive - Peripheral
What do central chemoreceptors detect
Changes in the [H+] in CSF around brain
What do changes in the [H+] in CSF around brain cause
Reflex stimulation of ventilation following a rise in [H+] (driven by raised PCO2 = Hypercapnea)
CO2 + H2O produces
H2CO3 (carbonic acid) which is converted to H+ and HCO3- (bicarbonate)
How can ventilation be reflexly inhibited
By a decrease in arterial PCO2 which reduces CSF [H+] causing hyper ventilation
What will central chemoreceptors not respond to
Direct changes in plasma [H+]
What will an increase in arterial Pco2 cause
Causes CO2 to cross blood brain barrier
Feedback occurs through the respiratory centres to increase ventilation
What do central chemoreceptors monitior
Pco2 indircetly in the CSF
What does a decrease in arterial Pco2 do
Slows ventilation rate
What do peripheral chemoreceptors detect
Changes in the arterial PO2 and [H+]
What do peripheral chemoreceptors cause
reflex stimulation of ventilation following a significant fall in arterial PO2 or a rise in [H+]
What do peripheral chemoreceptors respond to
Arterial PO2 not the oxygen content
In regards to peripheral chemoreceptors what normmaly accompanies and increased [H+]
Rise in arterial PCO2
What do changes in plasma pH cause
They alter ventilation through the peripheral chemoreceptor pathways
What happens if plasma pH falls ([H+] increases)
Ventilation will be stimulated (acidosis)
What happens if plasma pH increases ([H+] decreases)
Ventilation will be inhibited
E.g. vomiting (alkalosis)
In what direction will the equation move when ventilation is increased
To the left to blow off CO2 and lower [H+]
In what direction will the equation move when ventilation is decreased
To the right to retain CO2 and increase [H+]
What do descending neural pathways from the cerebral cortex to the respiratory motor neurones allow
A large degree of voluntary control over breathing
What can the descending neural pathways from the cerebral cortex to the respiratory motor neurones not overide
The involuntary stimuli such as arterial PCO2 or [H+]
Name 3 other ways in which breathing can be controlled
Breath holding
Hyperventilation
Respiration is inhibited when swallowing to avoid aspiration of foods or fluids into the airways
What does breathing in CO2 cause
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
What do barbiturates and opioids do
Depress the respiratory centre (overdose normally results in death because of respiratory failure)
What do gaseous anaesthetic agents do
Increase respiratory rate but decrease TV so decrease AV
What does nitrous oxide (commn sedative) do
Blunts peripheral chemoreceptor response to falling PaO2
Why is swallowing followed by expiration
So that any particles are dislodged outwards from the region of the glottis
