Control of Ventilation Flashcards
What is Dyspnea
Sensation of shortness of breath
What do the Pons respiratory centres do
Influence and modify activity of the medullary centres to smooth out transitions between inspiration and expiration
What does the Apneustic centre of the pons respiratory centre do
Sends signal to the Dorsal Respiratory Group (DRG) in the medulla to delay the inspiratory cut off from the pneumotaxic centre and vagus, it excites the inspiratory centres
What does the Pneumotaxic centre of the pons respiratory centre do
Acts as “off switch” neurons for inspiration. Stimulation of this centre terminates inspiration earlier to reduce tidal volume and cause higher respiratory frequency
What is the Dorsal Respiratory Group (DRG) also known as
The inspiratory centre
Where is the DRG located
Located near the root of the cranial nerve IX (glossopharyngeal) in the dorsomedial medulla (ventrolateral nucleus)
What does the DRG do
Excites the inspiratory muscles includes the diaphragm, external intercostals and the Ventral Respiratory Group (VRG) neurons
What inputs does the DRG receive
Pretty much all peripheral afferents (chemo., mechanism., proprio.) via the vagus and glossopharyngeal nerves
Apneustic centre
What do the inspiratory neurons of the Ventral Respiratory Group (VRG) activate
Accessory muscles of inspiration and external intercostals
What do the expiratory neurons of the Ventral Respiratory Group (VRG) activate
Internal intercostals and abdominal muscles
When are the expiratory neurons of the VRG active
Only during exercise but not during normal breathing
Where are the DRG and VRG located
In the Medulla Oblongata
What factor is the main driving force for breathing
PaCO2
Why are chemoreceptors more sensitive to CO2 than O2
Oxygen content of the blood decreases more slowly due to the large reservoir of oxygen attached to haemoglobin
What is the role of chemoreceptors
They provide the input to modify the rate and depth of breathing to maintain arterial PaCO2 at 40mmHg
What are the 2 kinds of chemoreceptor
Central
Peripheral
What are central chemoreceptors responsive to and what do they use to carry out their role
- responsive to increased arterial PaCO2
- Act by way of CSF [H+]
What are peripheral chemoreceptors responsive to
- Decreased arterial PaO2
- Increased arterial PaCO2
- Increased [H+]
Where are the central chemoreceptors located
0.2mm below the anterolateral surfaces of the medulla, close to the origins of the glossopharyngeal and vagus nerve
If PaCO2 increases what happens to the ventilation
It increases
What do the central chemoreceptors respond to
pH of the CSF.
How is carbonic acid formed in the CSF
CO2 combines with water to form carbonic acid that dissociates to form Hydrogen ions and bicarbonate
What body structure receives more blood flow than any other organ
The peripheral chemoreceptors
2000ml/100g/min
Despite the very high metabolic rate of the peripheral chemoreceptors, what keeps the capillary PO2 and PCO2 close to arterial values
the mad blood flow
What type of cell is a carotid body
chemoreceptor
What are the type 1 and type 2 cells of the carotid body
Type 1 = gloms cell
Type 2 = Sustentacular cell
What are the features of the glomus cells
- sensitive to local changes in PO2 (mainly), PCO2 and pH
- Lots of neurotransmitter cytoplasmic granules (Dop., NA., ACh.)
What are the features of the sustentacular cells
no granules function = ? Its an interstitial cel that wraps around glomus and nerve endings in the chemoreceptor
Inhibiting why channels leads to depolarisation in the glomus cell
K+ channels
What are the carotid and aortic bodies of the peripheral chemoreceptors sensitive to
Carotid = PaO2, PaCO2 and pH Aortic = PaO2, PaCO2 but not pH
Afferents of which nerves go to the carotid and aortic bodies of the peripheral chemoreceptors
Carotid = Glossopharyngeal Aortic = Vagus
Which bodies in the peripheral chemoreceptors respond the strongest
Carotid > Aortic
What structures in the medullary respiratory centres monitor arterial oxygen levels
Aortic and carotid bodies
What is needed for arterial PaO2 to become a major stimulus for increased ventilation
major drop in PaO2 (to 60mmHg)
How does PCO2 change as a stimulus if CO2 is not removed (like in emphysema and chronic bronchitis)
Chemoreceptors become unresponsive to PCO2
If CO2 isn’t removed and chemoreceptors become unresponsive what is then used as a stimulus
PaO2
If the pH falls does ventilation increase of decrease and what is this response mediated by
Ventilation increases and this is mediated by peripheral chemoreceptors
What are the 3 types of mechanoreceptors that are in the lungs and airways
Slowly adapting
Rapidly adapting
C-Fibre endings
What are the 3 mechanoreceptors innervated by
The vagus nerve
Pulmonary stretch receptors are responsible for which reflex
Hering-Breuer Reflex
What does stimulation of pulmonary stretch receptors cause when lungs are maximally inflated and when is this response important
Inhibits respiration - limiting tidal volume
Important in situations where there is a central drive increasing tidal volume - during exercise
What is unique about the firing of sensory signals of slowly adapting mechanoreceptors
they continue to fire as long as the stretch is held.
How are the pulmonary stretch receptors responsible for Respiratory Sinus Arrhythmia (tachycardia during I relative to E)
Stretch = Increased afferent vagal discharge --> Medullary Cardiovascular centre = Decreased parasympathetic and increased sympathetic activity = Increased Heart Rate
What are 2 types of unmyelinated free nerve endings involved in the mechanical control of respiration
Pulmonary C fibres
Bronchial C fibres
Where are Pulmonary C fibres (Juxta alveolar/J receptors) found and what are they sensitive to
Within the walls of pulmonary capillaries
Sensitive to products of inflammation (histamine, bradykinin etc)
What does the reflex of pulmonary c fibres result in
Rapid shallow breathing
Where are bronchial C fibres found
In the conducting airways
What are bronchial c fibres sensitive to
Products of inflammation
What does the reflex of bronchial c fibres do
bronchoconstriction
Increased airway vascular permeability
Hyperpnoea (deep inhalation)
Laryngeal constriction
What are irritant receptors
Respond to chemical and mechanical irritants
They have myelinated nerve endings
Name 2 upper airway irritant receptors
Nasal
Pharyngeal + Laryngeal
Branches of which afferent nerves are connected to nasal receptors
Trigeminal + Olfactory
What reflexes are nasal receptors responsible for
Sneezing
Diving - water instilled into the nose = apnea laryngeal closure, bronchoconstriction + bradycardia etc
Branches of which afferent nerves are connected to pharyngeal + laryngeal receptors
Laryngeal + Glossopharyngeal nerves
What reflexes are pharyngeal + laryngeal receptors responsible for
- Aspiration/sniff/swallowing reflexes
- Negative pressure induced abduction
Mechanoreceptors in the costovertebral joints are sensitive to what
Rib displacement
Why are the proprioceptors in the costovertebral joints though to be the main site of impulses causing conscious sensation of lung distension
The sensation is still present when the vagus is severed and input from the pulmonary and intercostal stretch receptors is lost
