SM 157a - Control of Breathing Flashcards
The PreBötC signals to the _________________, in order to generate [inspiration/expiration]
The PreBötC signals to the inspiratory bulbospinal neurons in the rostral ventral respiratory column** , in order to generate **inspiration
What is the difference between the Breur-Hering inspiratory terminating reflex and the Breur-Hering expieratory facilitating reflex?
They are two parts of the same reflex
- Inspiratory terminating reflex
- Activated when lung inflation is 3*VT
- Terminates current inspiration and initiates expiration
- Expiratory facilitating reflex
- Activated when lung inflation is prolonged
- Slows breathing
- Prolongs expiration
- Activates abdominal expiratory muscles
If the body’s response to increases in PaCO2 is to hyperventilate, why do patients with chronic respiratory insufficiency hypoventilate?
The body adapts to chronically elevated PaCO2
- Compensatory increases in arterial [HCO3-] lead to increased [HCO3-] in the brain
- This resets medullary (central) chemoreceptors, leading to decreased respiratory drive
- The body basicallly becomes more okay with chronic high levels of PaCO2
The parafacial respiratory group signals to the _________________, in order to generate [inspiration/expiration]
The parfacial respiratory group signals to the expiratory bulbospinal neurons in the caudal ventral respiratory column** , in order to generate **expiration
A sigh or augmented breath is a reflex caused by activation of the ____________ pulmonary stretch receptors
A sigh or augmented breath is a reflex caused by activation of the rapidly adapting pulmonary stretch receptors
Peripheral chemoreceptors begin to really respond to hypoxemia when PaO2 decreases below _____ mmHg
Peripheral chemoreceptors begin to really respond to hypoxemia when PaO2 decreases below 60 mmHg
What stimulus activates the slowly adapting pulmonary stretch receptors?
What is their response?
The slowly adapting pulmonary stretch receptors are activated by lung inflation or bronchoconstriction
They will continue rapid firing as long as inflation is maintained
They function to terminate the current inspiration and initiate expiration
Which pathophysiologic stimulus will most strongly activate the body’s ventilatory response?
- Increased PaCO2
- Decreased pH
- Decreased PaO2
a. Increased PaCO2
What does the pre Bötzinger complex (preBötC) do?
Where is it located?
The preBötC is responsible for generating inspiratory breathing rhythm
It is located in the rostral ventral respiratory column (VRC), which is located in the ventrolateral medulla
Describe the ventilatory response to increased PaCO2
Increased PaCO2 causes…
-
Central and peripheral chemoreceptor activation
- Central chemoreceptors have the strongest response
-
Increase alveolar ventilation by increasing minute ventilation (V̇E)
- There is a linear increase in V̇E as PaCO2 increases
- Steeper slope = more sensitive chemoreceptor
Most of the response to short-term decreases in pHa can be attributed to which receptors?
Peripheral chemoreceptors
Describe the body’s compensatory response to chronically elevated PaCO2
Chronically elevated PaCO2 causes…
- Compensatory increase in arterial [HCO3-] over days
- Due to increase in kidney retention of HCO3-
- Eventually, the brain [HCO3-] will increase
- This resets medullary (central) chemoreceptors
- Increased [HCO3-] in the brain decreases respiratory drive
- CO2 sensitivity is reduced
- The slope of the V̇E/PaCO2 curve decreases
- This resets medullary (central) chemoreceptors
Describe the central chemoreceptor response to lactic acidosis
The central chemoreceptors are not very good at responding to changes in pH; H+ ions don’t typically cross the blood-brain barrier
However, the central chemoreceptors are very responsive to high PaCO2 - they trigger a ventilatory response
Activation of c-fibers + rapidly adapting receptors results in a [cough/sneeze]
Activation of c-fibers + rapidly adapting receptors results in a cough
Why is V̇A/Q̇ higher in the apical regions of the lung than the basal regions (in an upright person)?
The apex of the lung has a lower compliance (-> lower V̇) and lower blood flow (Q̇) than the base.
However, the decreased compliance, and therefore decreased V̇, is less than the decrease in blood flow.
This means that V̇A/Q̇ will be higher in the apex of the lung than the base, if a person is sitting upright
Where are the slowly adapting pulmonary stretch receptors located?
Airway smooth muscle
Which pontomedullary cardiorespiratory cell group contains teh central pattern generator for expiration?
The parafacial respiratory group
Irritation above the oropharynx results in a [cough/sneeze]
Irritation above the oropharynx results in a sneeze
What stimulus activates the rapidly adapting pulmonary stretch receptors? (RARs)
What is the effect?
The RARs are also known as irritant receptors
They are activated by irritation to the airways
Activation ->
- Facilitates inspiratory efforts
- Contributes to airway protective reflexes
- Cough, sneeze
- Increases mucus production
- Bronchoconstriction
What does the ventral respiratory column (VRC) do?
Where is it located?
The VRC is the dominant site of nerual circuitry that generates breathing rhythm.
It is located in the ventrolateral medulla.
It contains the PreBötC which generates inspiratory rhythm, and the pFRG which generates expiratory rhythm.
What causes increased [HCO3-] in the brain?
What is the effect?
Increased [HCO3-] in the brain is caused by chronic hypercapnia (elevated PaCO2)
The result is decreased respiratory drive, leading to retention of CO2 in the blood
What is Rett syndrome?
What causes it?
A developmental disorder of the CNS due to a mutation in the x-linked Mecp2 gene
- Severe neurological symptoms
- Speech and movement disorders
- Irregular breathing (Cheyne-stokes)
- -> life-threatening apnea
- Onset 6-18 months
Where are the rapidly adapting pulmonary stretch receptors located?
Between airway epithelial cells in the trachea and larger bronchi
- Near postcapillary venules
- Activated by airway edema
- In epipharynx
- Activation -> aspiration reflex (strong inspiratory efforts)
Shallow, rapid breathing is a reflex caused by activation of the __________
Shallow, rapid breathing is a reflex caused by activation of the bronchopulmonary c-fibers
What does the parafacial respiratory group (pFRG) do?
Where is it located?
The pFRG is responsible for generating expiratory breathing rhythm
It is located in the caudal ventral respiratory column (VRC), which is located in the ventrolateral medulla
Which gas is the most potent pathophysiologic stimulus for breathing?
CO2
Ventilation can double wtih a 2 mmHg increase in PaCO2
What stimulates teh central chemoreceptors?
- High PaCO2
- Low pH
Central chemoreceptors are most responsive to High PaCO2
H+ ions don’t typically cross the blood-brain barrier, so there is a limited acute response to lactic acidosis
What stimulates the peripheral chemoreceptros in the carotid and aortic bodies?
- Low PaO2
- Low pHa
- High PaCO2
Irritation in or below the oropharynx results in a [cough/sneeze]
Irritation in or below the oropharynx results in a cough
The ventral respiratory column (VRC) is the dominant site for neural circuitry that generates breathing.
Within the VRC, which region is responsible for inspiratory rhythm?
Which region is responsible for expiratory rhythm?
Inspiratory: Pre Bötzinger complex (PreBötC)
Expiratory: Parafacial respiratory group (pFRG)
Activation of which receptors initiates the Breur-Hering inspiratory terminating reflex?
Slowly adapting pulmonary stretch receptors - when lung inflation is ~3*VT
This reflex works to terminate the current inspiration and initiate expiration
Activation receptors in the mucous membrane of the nose results in a [cough/sneeze]
Activation receptors in the mucous membrane of the nose results in a sneeze
Activation of which pulmonary mechanoreceptors…
Facilitates expiration?
Facilitates inspiration?
Expiration is facilitated by activation of the slowly adapting pulmonary stretch receptors
Inspiration is facilitated by activation of the rapidly adapting pulmonary strech receptors
Describe the Breur-Hering inspiratory terminating reflex
This reflex is mediated by slowly adapting pulmonary stretch receptors that signal to the brainstem to terminate the current inspiration and initiate expiration
It can also produce bronchodilation, prolong expiration, and activate abdominal expiraotry muscles
Which pontomedullary cardiorespiratory cell group contains the central pattern generator for inspiration?
The PreBötzinger complex
What causes Cheyne-stokes breathing?
What is the effect?
Cheyne-stokes breathing is caused by decreased sensitivity of central chemoreceptors due to decreased cardiac output
The effect is a delay between changes in PACO2 and detection by chemoreceptors. This can lead to life-threatening apnea
Which pontomedullary cardiorespiratory cell groups is important for the coordination fo respiratory control with activity in other systems?
The pontine respiratory group
Neurons involved in breathing are concentrated within which 3 regions of the medulla and the pons?
- Dorsal respiratory group (DRG)
- Ventral respiratory column (VRC)
- Pontine respiratory group (PRG)
Ventral respiratory column is the dominant site
If lung inflation continues into the expiratory period, which receptors are activated?
Which reflex is initiated?
Slowly adapting pulmonary stretch receptors initiate the Breuer-Hering expiratory facilitating reflex
- If lung inflation continues into the expiratory period, FRC increases and the slowly adapating pulmonary stretch receptors are activated
- This slows down breathing
- Expiration is prolonged
- Abdominal expiratory muscles are activated
What are C-fibers?
What do they do?
C-fibers are small, unmylinated nerve fibers near the alveoli
They are activated by the accumulation of pulmonary fluid or inhaled irriatants
When activated, they induce a rapid, shallow breathing pattern and produce a sensation of dyspnea
Where are central chemoreceptors located?
The retrotrapezoid nucleus
(Ventral to the facial nucleus near the ventral surface of the medulla)
Which receptors are the primary responders to hypoxia?
Peripheral chemoreceptors
Located in the carotid and aortic bodies
Activation of which pulmonary mechanoreceptors facilitates…
Bronchodilation?
Bronchoconstriction?
Bronchodilation is facilitated by activation of the slowly adapting pulmonary stretch receptors
Bronchoconstriction is facilitated by activation of the rapidly adapting pulmonary strech receptors
