Chemical Control of Breathing

Question 1

What are the sensors involved in the regulation of involuntary breathing rhythm?

Answer 1

central chemoreceptors
peripheral chemoreceptors
stretch receptors

Question 2

What do the central chemoreceptors measure?

Answer 2

pCO2 in the CSF via HCO3 at the medula

Question 3

What do the peripheral chemoreceptors measure?

Answer 3

the PO2, PCO2 and pH in the blood and mixed lung gases

Question 4

What sensors are the peripheral chemoreceptors?

Answer 4

carotid body

neuroepithelial bodies

Question 5

What do the stretch receptors do?

Answer 5

Hering-Breuer reflex
inhibit lung over-inflation
increase breathing frequency following rapid lung deflation

Question 6

Which breathing response can be altered by training?

Answer 6

the central chemoreceptors

Question 7

What has the biggest contribution to normal control of breathing?

Answer 7

central chemoreceptors - 80%

Question 8

What do the central chemoreceptors primarily detect?

Answer 8

pH changes caused by increase PaCO2

Question 9

What do the peripheral chemoreceptors primarily detect?

Answer 9

decrease in PaO2 in blood and airway

Question 10

Which breathing response is fastest?

Answer 10

the peripheral chemoreceptors

Question 11

What cannot cross the blood brain barrier?

Answer 11

HCO3 and H

Question 12

What does high HCO3 cause?

Answer 12

reaction reversal

Question 13

What does the reaction reversal of HCO3 do?

Answer 13

creates CO2 which can diffuse in to the CSF where HCO3 is made again

Question 14

Why is the reaction to HCO3 slower in the brain?

Answer 14

there is no carbonic anhydrase

Question 15

What allows small changes in pH to be detected?

Answer 15

there is no pH buffering system in the brain

Question 16

Where does the signal go from the medulla?

Answer 16

increased firing to DRG

Question 17

What change in pACO2 doubles total ventilation?

Answer 17

40-45mmHg

Question 18

Why does hypoxia make the response steeper?

Answer 18

hypoxia may bring central chemoreceptors closer to firing threshold

Question 19

What causes yawning?

Answer 19

relaxation gives pCO2 time to build up slowly overtime…yawn is a reboot through the CCR

Question 20

What may be used to overide the CCR response?

Answer 20

narcotics

Question 21

What is the adaptive ability of CCRs relevant to?

Answer 21

disease
high altitude
free diving
drug action

Question 22

How do free divers end up in shallow water black out?

Answer 22

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

Question 23

What are the peripheral chemoreceptors?

Answer 23

the carotid body - carotid sinus
aortic body - aortic arch
neuroepithelial bodies

Question 24

What is the issue with peripheral CRs?

Answer 24

they are only located in the arterial system and so cannot detect metabolic perturbations during exercise

Question 25

What is likely to have the biggest influence on breathing patterns during exercise?

Answer 25

conscious control

Question 26

When will peripheral chemoreceptors influence breathing?

Answer 26

only if arterial pO2 falls such as exercise with hypoxia or hypoxic respiratory diseases

Question 27

What do PCRs do at altitude?

Answer 27

act to maintain alveolar pO2 closer to inspired pO2

Question 28

What do PCRs respond to?

Answer 28

primarily hypoxia but because of the Bohr-Haldane effects also the pH and PaCO2

Question 29

Why are PCRs not in the venous vasculature?

Answer 29

they are an emergency response

Question 30

How can you get the rate of ventilation per litre of oxygen consumed?

Answer 30

Dividing ventilation rate per minute by oxygen consumption

Question 31

Why is breathing at altitude exhausting?

Answer 31

there are more breaths per ml of O2 consumed

Question 32

What happens to the work of breathing at altitude?

Answer 32

it utilises almost all the O2 consumed hence need suplementary oxygen

Question 33

How does the cell transmit hypoxia signals?

Answer 33

depolarises the cell through O2 or pH sensor Opens VGCC NT release Glossopharyngeal nerve goes to DRG and RRG

Question 34

What are the responses of the brain stem?

Answer 34

hypoxic ventilatory response | hypoxic pulmonary vasoconstrictor response

Question 35

What channels sense O2 and pH levels?

Answer 35

TASK 3 K+ channels

Question 36

What is the effect of O2 and hypoxia on the TASK channel?

Answer 36

closes the channel - both proton and hypoxia create a larger effect

Question 37

How does acidosis cause closure ?

Answer 37

acidifcation of the cytosol stimulates closure of a hinge-like loop across the pore of the channel

Question 38

How does hypoxia stimulate closure?

Answer 38

suppressing the rate at which IC superoxide is made by NADPH oxidase - which normally prevents hinge loop from closing