Chemical Control of Breathing Flashcards
What are the sensors involved in the regulation of involuntary breathing rhythm?
central chemoreceptors
peripheral chemoreceptors
stretch receptors
What do the central chemoreceptors measure?
pCO2 in the CSF via HCO3 at the medula
What do the peripheral chemoreceptors measure?
the PO2, PCO2 and pH in the blood and mixed lung gases
What sensors are the peripheral chemoreceptors?
carotid body
neuroepithelial bodies
What do the stretch receptors do?
Hering-Breuer reflex
inhibit lung over-inflation
increase breathing frequency following rapid lung deflation
Which breathing response can be altered by training?
the central chemoreceptors
What has the biggest contribution to normal control of breathing?
central chemoreceptors - 80%
What do the central chemoreceptors primarily detect?
pH changes caused by increase PaCO2
What do the peripheral chemoreceptors primarily detect?
decrease in PaO2 in blood and airway
Which breathing response is fastest?
the peripheral chemoreceptors
What cannot cross the blood brain barrier?
HCO3 and H
What does high HCO3 cause?
reaction reversal
What does the reaction reversal of HCO3 do?
creates CO2 which can diffuse in to the CSF where HCO3 is made again
Why is the reaction to HCO3 slower in the brain?
there is no carbonic anhydrase
What allows small changes in pH to be detected?
there is no pH buffering system in the brain
Where does the signal go from the medulla?
increased firing to DRG
What change in pACO2 doubles total ventilation?
40-45mmHg
Why does hypoxia make the response steeper?
hypoxia may bring central chemoreceptors closer to firing threshold
What causes yawning?
relaxation gives pCO2 time to build up slowly overtime…yawn is a reboot through the CCR
What may be used to overide the CCR response?
narcotics
What is the adaptive ability of CCRs relevant to?
disease
high altitude
free diving
drug action
How do free divers end up in shallow water black out?
hyperventilation drives initial pACO2 down
O2 consumed during dive
low CCR sensitivity due to training
fails to trigger breathing response in time to prevent severe hypoaemia
loss of conciousness
What are the peripheral chemoreceptors?
the carotid body - carotid sinus
aortic body - aortic arch
neuroepithelial bodies
What is the issue with peripheral CRs?
they are only located in the arterial system and so cannot detect metabolic perturbations during exercise
What is likely to have the biggest influence on breathing patterns during exercise?
conscious control
When will peripheral chemoreceptors influence breathing?
only if arterial pO2 falls such as exercise with hypoxia or hypoxic respiratory diseases
What do PCRs do at altitude?
act to maintain alveolar pO2 closer to inspired pO2
What do PCRs respond to?
primarily hypoxia but because of the Bohr-Haldane effects also the pH and PaCO2
Why are PCRs not in the venous vasculature?
they are an emergency response
How can you get the rate of ventilation per litre of oxygen consumed?
Dividing ventilation rate per minute by oxygen consumption
Why is breathing at altitude exhausting?
there are more breaths per ml of O2 consumed
What happens to the work of breathing at altitude?
it utilises almost all the O2 consumed hence need suplementary oxygen
How does the cell transmit hypoxia signals?
depolarises the cell through O2 or pH sensor
Opens VGCC
NT release
Glossopharyngeal nerve goes to DRG and RRG
What are the responses of the brain stem?
hypoxic ventilatory response
hypoxic pulmonary vasoconstrictor response
What channels sense O2 and pH levels?
TASK 3 K+ channels
What is the effect of O2 and hypoxia on the TASK channel?
closes the channel - both proton and hypoxia create a larger effect
How does acidosis cause closure ?
acidifcation of the cytosol stimulates closure of a hinge-like loop across the pore of the channel
How does hypoxia stimulate closure?
suppressing the rate at which IC superoxide is made by NADPH oxidase - which normally prevents hinge loop from closing
