Phys - Control of breathing Flashcards
Where does involuntary control of breathing happen in brain?
Pons and medulla (brainstem)
Three brainstem neuron groups involved in breathing
- Medullary respiratory center
- Apneustic center (pons)
- Pneumotaxic center (pons)
Two divisions of medullary respiratory center and their functions
- Inspiratory center - controls rate of breathing by setting frequency
- Expiratory center - usually a passive process so really only active during exercise
How do chemoreceptors relay info to inspiratory center?
CN 9 and 10
How does inspiratory center relay motor output to diaphragm?
Phrenic N
What does the apneustic center do?
Prolong inspiration by exciting inspiratory center
What does pneumotaxic center do?
Regulates respiratory rate; inhibits inspiratory center so decrease rate
Describe how breathing rate is set by inspiratory center.
Rhythm-generating neurons have short bursts of AP that suddenly stop; corresponds with diaphragmatic contraction followed by quiescence
Three central inputs to medulla
- Cerebrum
- Apneustic center
- Pneumotaxic center
5 peripheral inputs to medulla
- Pulmonary stretch receptors
- Baroreceptors
- Gamma receptors
- Respiratory muscles
- Carotid and aortic bodies (chemoreceptors)
What do gamma receptors do?
They’re in muscle and sense PO2 to determine whether muscle moved
Normal PO2
95
Normal PCO2
40
Normal pH
7.4
Two divisions of chemoreceptors
Central and peripheral
Goal of central chemoreceptors
Short-term regulation of arterial gases by responding to changes in PaCO2
BBB is impermeable to ____ and permeable to ____
HCO3- and H+
CO2
If BBB is impermeable to H+, how do H+-sensitive chemoreceptors sense a change in pH?
CO2 diffuses into CSF and forms H+ and HCO3-
Reduced pH sensed by central chemoreceptors has what effect on respiratory rate?
Increase (blow off more CO2)
What does the HCO3- formed in the CSF do?
Diffuses across BBB via an unknown transporter to whichever side has a lower pH
Receptors in aortic body vs. carotid body
Aortic = O2 and CO2 only Carotid = O2, CO2, and H+
How do peripheral chemoreceptors send info to medulla?
CN 9 and 10
When do O2 chemoreceptors stimulate medulla?
At PaO2<60 mmHg
remember this is when O2-Hb curve becomes steep
What role do CO2 chemoreceptors play?
Not as important as central H+ chemoreceptors or peripheral O2 chemoreceptors
What affects PaCO2?
NOTHING but VCO2/Valv!!!!!
Explain how central respiratory drive gets reset in pt with chronic lung disease.
Can’t get air out –> increased PaCO2 –> decreased pH of CSF –> can’t increase ventilation b/c of lung disease but pH of brain is too high –> HCO3- enters brain via that unknown transporter and raises pH –> pH of brain back to normal despite increased PaCO2
What would happen if pt with chronic lung disease was suddenly taken off ventilator?
They’re PaCO2 set point is higher than normal; once taken off ventilator they’re PaCO2 would drop so they’d stop breathing until it went up to new set point; must wean off vent to reset set point
Mechanism for carotid body-mediated stimulation of medullary respiratory center
O2-sensitive K+ channels senses low PaO2 –> inhibits channel –> cell depolarizes –> sends excitatory signal via CN 9 –> medullary respiratory center stimulated –> low PaO2 causes increased ventilation
Which determines ventilation via peripheral chemoreceptors: content of O2 or arterial O2?
Arterial
What is the relationship between PaCO2/pH and PaO2?
Increased PaCO2/decreased pH increases the sensitivity of PaO2 chemoreceptors such that PaO2<70 results in rapid ventilation
Explain how central respiratory drive gets reset at high altitudes
(Central chemoreceptors insensitive to PaO2 so must work via PaCO2/pH)
Peripheral receptors sense decreased PaO2 –> increase ventilation –> decreased PCO2 –> should decrease ventilation but HCO3- moves out of brain –> brain pH normal at lower CO2 –> reset
Explain via alveolar gas equation how resetting central respiratory drive increases PAO2 at lower PACO2
PAO2 = PIO2 - PaCO2/R
Decreased PaCO2 = increased PAO2
How does acetazolamide prevent mountain sickness?
High altitudes cause respiratory alkalosis (reset to lower PaCO2); acetazolamide (CA inhibitor) wastes HCO3- through kidney to create compensatory metabolic acidosis
How does plasma pH affect VA?
H+ sensed by peripheral chemoreceptors in carotid body and directly stimulate medullary respiratory center; respiratory compensation for metabolic acidosis
Why is hyperventilation a feature of DKA?
Decreased insulin –> increased fat breakdown –> increased fatty ACIDS –> decreased pH –> peripheral H+ chemoreceptors in carotid body activated –> medullary respiratory center activated –> increased VA
