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Respiratory > Week 5 - Chemical control of breathing > Flashcards

Week 5 - Chemical control of breathing Flashcards

1
Q

How does increasing breathing correct hypoxia and hypercapnia?

A
  • More O2 taken in so increased pO2

- More CO2 breathed off so decreases pCO2

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2
Q

Define hyper/hypoventilation

A

-Ventilation increase/decrease without a change in metabolism

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3
Q

What happens to pO2 or pCO2 during hyperventilation?

A

-pO2 rises and pCO2 falls

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4
Q

What effect does hypoventilation have on pO2 and pCO2?

A

-pO2 decreases pCO2 increases

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5
Q

What will happen if pO2 decreases without a change in pCO2?

A

-Increased breathing to correct pO2 but hypocapnia will ensue

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6
Q

At what kPA can pO2 reach before O2 saturation is affected?

A

-8

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7
Q

If pCO2 rises without a change in bicarb what happens to plasma pH?

A

-Decreases

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8
Q

What effect does pH have on calcium?

A

-If pH rises above 7.6 free ca conc drops leading to tetany

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9
Q

What is the physiological cause of respiratory acidosis/alkalosis?

A
  • acidosis -> Hypercapnia (increased pCO2)

- Alkalosis -> hypocapnia (decreased pCO2)

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10
Q

What can compensate for changes in pCO2?

A

-HCO3-

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11
Q

How is resp acidosis compenasted for?

A

-Increase in HCO3- by kidneys

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12
Q

How is resp alkalosis compensated for?

A

-Decreased bicarb by kidneys

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13
Q

Is compensation for respiratory acid-base distrubances immediate?

A

-No takes 2-3 days

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14
Q

What causes metabolic acidosis?

A

-Acids produced by metabolically active tissues reacting with HCO3 reducing its plasma concentration

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15
Q

How is metabolic acidosis compensated for?

A

-Increased ventilation to lower pCO2

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16
Q

When does metabolic alkalosis occur? When does this most commonly occur?

A
  • When there is a rise in plasma HCO3 concentration

- After vomiting (H+ decreases which causes HCO3 to rise as not being used up)

17
Q

What compensates for metabolic alkalosis and why is this limited?

A
  • Decreased breathing to increase pCO2

- Limited by increasing risk of hypoxia

18
Q

What determines plasma ph?

A

-The ratio of HCO3 to CO2

19
Q

What controls the rate of ventilation?

A

-Chemoreceptors located in the CNS and the periphery work to feed information about pO2 and pCO2 back to the respiratory control centre in the brainstem which adjusts accordingly

20
Q

How do peripheral chemoreceptors work?

A
  • Sense large falls in pO2 in the fluid they are exposed to
  • Causes increased breathing, increased HR (deliver more volume and thus more O2) and changes in bloodflow distribution (prioritise kidneys/brain)
21
Q

How do central chemoreceptors work?

A
  • Detect small changes in arterial pCO2 via CO2 diffusing across BBB into CSF -> broken down by CA and chemoreceptors detect level of H+
  • Rise in pCO2 increases ventilation to decrease CO2
  • Decrease in pCO2 decreases ventilation to increase CO2
22
Q

What is the response to persistently high pCO2 by the chemoreceptors?

A

-Stimulate choroid plexus cells to produce HCO3 for csf as cannot cross BBB

23
Q

Why is the choroid plexus so sensitive to pCO2 changes?

A
  • HCO3 cannot cross BBB so has no buffering capacity

- Elevated CO2 -> increases H+ in CSF whilst HCO3 is constant and CSF pH falls

24
Q

What is the short-term outcome of activation of central chemoreceptors?

A

-Alter ventilation

25
Q

How do the central chemoreceptors determine what pCO2 keeps CSF pH steady?

A
  • Persistently long changes in pCO2 result in the choroid plexus cells producing HCO3
  • Once the HCO3 increases and the pCO2 has been matched so pH is normal, the control system is set at that level of pCO2
26
Q

Describe what will happen regarding the chemoreceptors if there is persisting hypoxia with low pCO2

A
  • Hypoxia detected by peripheral chemoreceptors -> increased ventilation
  • Decreases pCO2 further
  • CSF compensates for altered pCO2 by adding H+ into CSF and central chemoreceptors accept pCO2 as normal
27
Q

Describe what will happen regarding the chemoreceptors in persistent hypercapnia

A
  • Detected by chemoreceptors as pH of CSF decreases
  • Breathing is stimulated
  • Acidic pH is undesirable for neurones and the choroid plexus pumps HCO3- into CSF
  • Chemoreceptors accept this new high pCO2 as normal
28
Q

Why do you have to be careful when administering high flow oxygen to someone with Co2 retention (regarding chemoreceptors)?

A

-Because the central chemoreceptors have reset to the steady pCO2 and the pH of the CSF is normal, respiratory drive is driven by low oxygen concentration. Administering high flow oxygen abolishes this and hypoventilation occurs

29
Q

What is hypercapnia? hypocapnia?

A

-Rise/fall in CO2

Respiratory (17 decks)

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