Physiology: Control of Ventilation Flashcards
Which nerves are stimulated in ventilation?
Stimulation from skeletal muscles of inspiration - ie the phrenic nerve to the diaphragm and intercostal nerves to the external intercostal muscles
Where are the respiratory control centres?
Pons and the medulla
Is respiration subconscious?
Normally yes however can be voluntarily modulated
Where does signalling to the respiratory system occur on the spinal cord?
C3-5
C3,4,5 keeps the diaphragm a alive
What is the function of the Respiratory centres?
Set automatic rhythm by co-ordinating firing smooth and repetitive action potentials in the Dorsal Respiratory Group (DRG) which travel to the inspiratory muscles
Adjusting the rhythm to stimuli
What modulates the Respiratory Centres?
- Emotion (Limbic System)
- Voluntary Over-ride (Higher brain centres)
- Mechano-sensory input from thorax (stretch sensitive)
- Chemical composition of blood (chemoreceptors)
What is the most significant modulator of respiratory centres?
Chemoreceptor input
What does the Dorsal Respiratory Group of neurons (DRG) supply?
Inspiratory muscles through phrenic and intercostal nerves
What does the Ventral Respiratory Group of neurons (VRG) supply?
Tongue
Pharynx
Larynx
Expiratory Muscles
What are the 2 types of Chemoreceptors?
Peripheral (Secondary Ventilatory Control) and Central (Primary Ventilatory Control)
Where are the Central Chemoreceptors found?
Medulla
What do Central Chemoreceptors Detect?
Changes in H+ concentration in CSF of the brain
What does a rise of H+ ions caused by raised PCO2 ie hypercapea?
Stimulates Ventilation
Does Ventilation directly respond to changes H+ concentration in plasma?
No
Can CO2 cross the blood brain barrier?
Yes
Can H+ cross the blood brain barrier?
No
How do central chemoreceptors monitor partial arterial pressure of CO2?
The monitor PCO2 indirectly
What products are formed when CO2 crosses the blood brain barrier?
Bicarbonate and H+
The receptors respond to H+
What does increased arterial PCO2 do the ventilation?
Increases Ventilation Rate
What does decreased arterial PCO2 do to ventilation?
Slows Ventilation Rate
Define the condition Hypoxic Drive?
De-sensitivity to PCO2 and instead relys on PO2 to stimulate ventilation
What Disease can cause hypoxic drive?
Chronic Lung Disease due to the elevated PCO2
Where are the Peripheral Chemoreceptors found?
Carotid and aortic bodies
What do peripheral chemoreceptors detect?
Changes in arterial PO2 (ie arterial oxygen pressure not total oxygen content) and H+ concentration (related to PCO2 in arteries)
How do Peripheral Chemoreceptors have an effect of ventilation?
Reflex stimulation of ventilation after a fall of PO2 or rise in H+ concentration
How does a fall in plasma pH affect ventilation?
Peripheral chemoreceptors detect increase [H+] and ventilation will be stimulated due to acidosis
How does increase in plasma pH affect ventilation?
Peripheral chemoreceptors detect decrease in [H+] (through vomiting) and ventilation will be inhibited due to alkalosis
How can we control our breathing?
Neural pathway from cerebral cortex to Resp motor neurons allows voluntary control
Are we able to overide our involuntary control?
No due to our chemoreceptors take primary control
When is ventilation reflexly inhibited?
Increase in PO2 in arteries and decrease in arterial PCO2 causing Hyperventilation
What does breathing in CO2 into our lungs cause to our body?
Bodies are programmed to get rid of CO2 therefore increased alveolar partial pressure of CO2 decreases pressure gradient and therefore increased arterial pressure of CO2 causing high distress
What is more uncomfortable, high PaCO2 and normal PaO2, or low PaO2 and No PaCO2?
High PaCO2 and normal PaO2 as your body is made to get rid of CO2
What happens respiration during swallowing?
Respiration is inhibited and is followed by expiration to remove any left over food going down the epiglottis
Name some drugs that have an effect on the Resp System
Barbiturates and opioids - depress Resp system
Anaesthetic agents increase RR
Nitrous Oxide (NO) blunts peripheral chemoreceptors response to PaO2 falling
Why shouldn’t NO be used on patients who have chronic Lung Disease?
As the patients rely on hypoxic drive
