22 - modulation of breathing Flashcards
what 3 things do chemoreceptors respond to?
PO2, PCO2, and pH
Where are the carotid bodies located?
in the bifurcation of the common carotid artery into the external and internal carotid arteries
What are the aortic and carotid bodies innervated by?
aortic - Vagus nerve
carotid - glossopharyngeal
Where are aortic bodies located?
in the aortic arch?
What are the similarities between aortic and carotid bodies?
they share the same afferents and are near their respective sinuses
What are in the carotid and aortic sinuses?
baroreceptors, they share heir innervation with the respective chemoreceptors
What is the carotid body made of?
glomus cells
What happens when there is a fall in oxygen?
AP’s go haywaire
there is a graded response of hypoxia
What does the carotid body contribute to ventilatory responses?
all ventialtory response to PO2 changes
it is also stimulated by metabolic acidosis
contributes 20% of the response to CO2
What is the relationship between PaO2 and chemoafferent discharde frequency?
higher PaO2, lower chemoafferent discharge frequency, this relationshiip is a hyperbolic function
What effect does metabolic acidosis have on the stimulus response curve of the carotid body?
shifts it up and right
basically increases the amount of discharge for any given level of oxygen
How does hypoxia lead to neurosecretion?
reduces ATP production AMP increases activation of AMPK inhibits BK / TASK K+, inhibiting K+ efflux membrane depolarisation Ca2+ influx through opened VGC's neurosecretion
What happens to the carotid body in its’ response to hypoxia?
gets bigger, hyperplasia, hypertrophy
this can be useful at altitude
but it can cause a benign carotid body tumour
Which areas of the brain are associated with central chemoreceptors?
ventral medulla:
rostral zone, intermmediate zone, caudal zone, all around the basilar artery
What proportion of the ventilatory response to CO2 is provided for by central chemoreceptors?
Do they respond to Hypoxia?
80%
No, but they are inhibited by it
What lies between the neurones of central chemoreceptors and the blood?
How can central chemoreceptors still be stimulated?
BBB
stops H+ from crossing, so CO2 crosses and then forms H+ instead
How do central chemoreceptors acclimatise?
in extended periods of adverse alkalosis / acidosis, the pH is gradually attenuated by active transport of HCO3- from blood to ECF / CSF or other way round
Is CCR acclimatisation fast?
Why?
the BB makes it a slow response
What happens to patients with chronic lung disease and their attentuation?
they have an attenuated ability to increase ventilation in a high CO2
What is the relationship between arterial blood pH and CSF steady state pH?
linear relationship, an increase in arterial pH will see an increase in CSF steady state pH
Which of variations in PaCO2 and H+ changes unrelated to ventilation, have a greater effect on CSF steady state pH over a given arterial pH change?
acid-base changes due to variations in PaCO2
What effect will CSF pH have on ventilation?
an increase in CSF pH will decrease ventilation
What is the relationship betweenPaCO2 and alveolar ventilation?
linear response curve (but steep!!!! so big increases in ventilation for small PaCO2 increments)
How does the relationship between PaCO2 and alveolar ventilation change with:
low PaO2
High PaO2 or anaesthesia?
low - steeper line shifted left
high / A - smaller gradient shifted right
what is dyspoea?
shortness of breath
What is the common afferent between all 3 of pulmonary mechanical receptor?
Vagus nerve to DRG
What are the 3 types of pulmonary mechanical receptors?
rapidly adapting irritant receptors
slowly adapting stretch receptors
J type (Juxtacapillary) or C-type fibres
Where are rapidly adapting irritant receptors, what are they activated by, and what do they stimulate?
between airway epithelia (large airway)
activated by sudden lung distension and certain irritants
cause cough, bronchoconstriction, and hyperpnea
What is the character of the signal sent by RAIR’s?
rapidly adapting within 1s of response, decrease in discharge over time
Where are slowly adapting stretch receptors located, what are they activated by, and what do they stimulate?
between smooth muscle cells in trachea and lower airway
activated by lung distention
Hering Breuer reflex, bronchodilation and tachycardia
What is the Hering breuer reflex?
What significance does it have for humas?
inhibtion of inspiration and promotion of expiration
if you rapidly inspire it’s terminated quite quickly by this reflex
younger humans have a greater reflex, implying it’s a defence mechanism (cortical development may take over)
What is the character of the signal sent by SASR’s?
slowly adapting, so the firing rate is sustained during the stretch
Where are J type fibres, what to the sense, and what do they stimulate?
terminals on alveoli and pulmonary capillaries
activated by interstitial fluid, pulmonary congestion, oedema
they cause apnoea, bronchocontriction, increases mucus secretion, hypotension, bradycardia
What is the characteristic of the signal sent by J-type fibres?
rapidly adapting (to change), but slowly conducting as they are C-type
