Phys - Control of breathing

Question 1

Where does involuntary control of breathing happen in brain?

Answer 1

Pons and medulla (brainstem)

Question 2

Three brainstem neuron groups involved in breathing

Answer 2

1. Medullary respiratory center
2. Apneustic center (pons)
3. Pneumotaxic center (pons)

Question 3

Two divisions of medullary respiratory center and their functions

Answer 3

1. Inspiratory center - controls rate of breathing by setting frequency
2. Expiratory center - usually a passive process so really only active during exercise

Question 4

How do chemoreceptors relay info to inspiratory center?

Answer 4

CN 9 and 10

Question 5

How does inspiratory center relay motor output to diaphragm?

Answer 5

Phrenic N

Question 6

What does the apneustic center do?

Answer 6

Prolong inspiration by exciting inspiratory center

Question 7

What does pneumotaxic center do?

Answer 7

Regulates respiratory rate; inhibits inspiratory center so decrease rate

Question 8

Describe how breathing rate is set by inspiratory center.

Answer 8

Rhythm-generating neurons have short bursts of AP that suddenly stop; corresponds with diaphragmatic contraction followed by quiescence

Question 9

Three central inputs to medulla

Answer 9

1. Cerebrum
2. Apneustic center
3. Pneumotaxic center

Question 10

5 peripheral inputs to medulla

Answer 10

1. Pulmonary stretch receptors
2. Baroreceptors
3. Gamma receptors
4. Respiratory muscles
5. Carotid and aortic bodies (chemoreceptors)

Question 11

What do gamma receptors do?

Answer 11

They’re in muscle and sense PO2 to determine whether muscle moved

Question 12

Normal PO2

Answer 12

95

Question 13

Normal PCO2

Answer 13

40

Question 14

Normal pH

Answer 14

7.4

Question 15

Two divisions of chemoreceptors

Answer 15

Central and peripheral

Question 16

Goal of central chemoreceptors

Answer 16

Short-term regulation of arterial gases by responding to changes in PaCO2

Question 17

BBB is impermeable to ____ and permeable to ____

Answer 17

HCO3- and H+

CO2

Question 18

If BBB is impermeable to H+, how do H+-sensitive chemoreceptors sense a change in pH?

Answer 18

CO2 diffuses into CSF and forms H+ and HCO3-

Question 19

Reduced pH sensed by central chemoreceptors has what effect on respiratory rate?

Answer 19

Increase (blow off more CO2)

Question 20

What does the HCO3- formed in the CSF do?

Answer 20

Diffuses across BBB via an unknown transporter to whichever side has a lower pH

Question 21

Receptors in aortic body vs. carotid body

Answer 21

Aortic = O2 and CO2 only
Carotid = O2, CO2, and H+

Question 22

How do peripheral chemoreceptors send info to medulla?

Answer 22

CN 9 and 10

Question 23

When do O2 chemoreceptors stimulate medulla?

Answer 23

At PaO2<60 mmHg

remember this is when O2-Hb curve becomes steep

Question 24

What role do CO2 chemoreceptors play?

Answer 24

Not as important as central H+ chemoreceptors or peripheral O2 chemoreceptors

Question 25

What affects PaCO2?

Answer 25

NOTHING but VCO2/Valv!!!!!

Question 26

Explain how central respiratory drive gets reset in pt with chronic lung disease.

Answer 26

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

Question 27

What would happen if pt with chronic lung disease was suddenly taken off ventilator?

Answer 27

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

Question 28

Mechanism for carotid body-mediated stimulation of medullary respiratory center

Answer 28

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

Question 29

Which determines ventilation via peripheral chemoreceptors: content of O2 or arterial O2?

Answer 29

Arterial

Question 30

What is the relationship between PaCO2/pH and PaO2?

Answer 30

Increased PaCO2/decreased pH increases the sensitivity of PaO2 chemoreceptors such that PaO2<70 results in rapid ventilation

Question 31

Explain how central respiratory drive gets reset at high altitudes

Answer 31

(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

Question 32

Explain via alveolar gas equation how resetting central respiratory drive increases PAO2 at lower PACO2

Answer 32

PAO2 = PIO2 - PaCO2/R

Decreased PaCO2 = increased PAO2

Question 33

How does acetazolamide prevent mountain sickness?

Answer 33

High altitudes cause respiratory alkalosis (reset to lower PaCO2); acetazolamide (CA inhibitor) wastes HCO3- through kidney to create compensatory metabolic acidosis

Question 34

How does plasma pH affect VA?

Answer 34

H+ sensed by peripheral chemoreceptors in carotid body and directly stimulate medullary respiratory center; respiratory compensation for metabolic acidosis

Question 35

Why is hyperventilation a feature of DKA?

Answer 35

Decreased insulin –> increased fat breakdown –> increased fatty ACIDS –> decreased pH –> peripheral H+ chemoreceptors in carotid body activated –> medullary respiratory center activated –> increased VA