Control of Ventilation Flashcards
Which specific nerve stimulates the muscles required for inspiration?
Phrenic nerves
C3-5
Which specific nerve stimulates the muscles required for expiration?
Intercostal nerves
Which type of nerve control ventilation on inspiration?
Somatic motor
What will happen to the heart if its nerve supply were to be cut off?
Would the lungs have the same effect?
It would continue to pump as it has its own intrinsic rhythm.
No, lungs would cease to breathe without nerve supply (i.e. spinal cord severed above C3-5)
Where is the actions of ventilation controlled from?
ill defined respiratory centres in the pons and medulla (brain stem).
What do the DRG and VRG do?
They co-ordinate the firing of the smooth repetitive cyclic activation of neurons responsible for respiratory cycle.
What does the DRG control?
Which nerves does it utilise?
Muscles for inspiration via .the phrenic and intercostal nerves.
What does the VRG control?
Muscles for expiration (some inspiration), tongue, pharynx and larynx muscles.
What is the main function of the VRG, particularly on expiration?
It maintains tone and patency of upper airways, therefore very important during the expiratory phase even during passive expiration as it maintains tone of pharynx, larynx and tongue muscles.
How can emotions have an effect on respiratory rate?
Limbic system is connected to the respiratory system.
Which part of the brain has the ‘final say’ when it comes to ventilation?
The brain stem (pons and medulla)
It’s stimulation can be overridden by voluntary signals from the higher brain centres but not completely (e.g. you cant hold your breath until you die).
What is the purpose of stretch receptors in the thoracic wall?
They are essentially a safety mechanism.
Stretch receptors in the thoracic wall detect stretch at full inspiration (i.e. at threshold) and respond by creating a reflex inhibition of expiration to prevent over-inflation of the alveoli (i.e. prevents rupture).
How does chemical composition of the blood affect respiratory rate?
Chemical chemoreceptors detect changes and subconsciously alter ventilation.
There are central and peripheral chemoreceptors.
Where are central chemoreceptors located?
Medulla
What is meant by the central chemoreceptors respond ‘indirectly’ to changes in CO2?
Central chemoreceptors respond directly to changes in H+ in the CSF, however H+ ions are unable to cross the blood brain barrier.
CO2 (a gas) is able to cross the blood-brain barrier and when it does, it creates more bicarbonate and H+ ions in the CSF. It is these H+ ions that bind to chemoreceptors.
What is the main thing dictating our rate and depth of breathing (essentially our ventilation)?
PaCO2 (not pH, not PaO2)
How does the central chemoreceptors respond to an increase in PaCO2 (i.e. hypercapnea)?
Increased PaCO2 Increased CO2 in CSF Increased H+ in CSF H+ binds to chemoreceptors Causes reflex stimulation of ventilation Hyperventilation kicks in to bring down CO2 levels to normal values.
When would the central chemoreceptors cause reflex inhibition of ventilation?
When CO2 levels fall
Hypoventilation would bring values back to normal.
When you hold your breath for a period of time, what is causing the forced sensation to want to inspire more air?
It is the build up of CO2
In free diving, why is it dangerous to hyperventilate before the dive in order to blow of CO2 levels?
Hyperventilating before going under water to blow of CO2 levels means they can hold their breath for longer as they lose that drive to breathe.
This can be quite dangerous if your O2 levels fall before you feel the drive to breathe again then you lose consciousness under water and drown.
10% increase in PaCO2 leads to a _____% increase in ventilation.
CO2 is extremely ______ to cells.
100%
toxic
What is meant by ‘Hypoxic drive’?
Ventilation is driven by hypoxia, by a fall in O2 rather than an increase in CO2 (which would be by central chemoreceptors).
Why do many people suffering from chronic lung disease rely more on their peripheral chemoreceptors as opposed to their central chemoreceptors?
Because they become desensitised to high levels of CO2 in the body and their central chemoreceptors are less efficient.
Their ventilation is driven by their peripheral chemoreceptors which detect changes in PaO2.
Where are peripheral chemoreceptors found?
Carotid and aortic bodies