8 Chemical Control of Breathing Flashcards

1
Q

What is hypoxaemia?

A

Fall in arterial pO2

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2
Q

What do hypocapnia and hypercapnia mean?

A
  • Hypercapnia: Rise in alveolar (hence arterial) pCO2
  • Hypocapnia: Fall in alveolar (hence arterial) pCO2
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3
Q

Hypoventilation can result in respiratory acidosis. Explain why?

A

pH has decreased and ventilation rate decrease

Removal of CO2 from lungs= less rapid

pCO2 in alveoli has increased

[dissolved CO2] increases relative to [HCO3-] so ratio not 20:1

(Opposite for hyperventilation)

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4
Q

How do the kidneys respond to persistent respiratory acidosis?

A

Reduce excretion of HCO3-

(Opposite for hyperventilation)

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5
Q

What happens to the HCO3- concentration in the blood if there is excess metabolic production of acid (eg diabetic ketoacidosis)? What is the consequence of this?

A

Excess acid- buffered by HCO3- so used up–> concentration decreases

pH falls- metabolic acidosis

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6
Q

What are the 2 ways in which disturbances in the pH of the blood can be countered?

A
  • Alteration of alveolar pCO2 - alter ventilation rate
  • Corrected by kidneys (excretion of HCO3-)
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7
Q

What effect will these changes have on ventilation rate?

Drop in pO2

Large increase in pCO2

Drop in pH

A
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8
Q

How are the ventilation changes brought about (as a result of changes in pO2/pCO2/pH)?

A

Chemoreceptors- detect changes in arterial pO2/pCO2/pH

Send impulses to respiratory centres in brainstem–> modulate rate and depth of ventilation

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9
Q

What are the 2 types of chemoreceptors that respond to changes in blood pO2/pCO2/pH?

A

Peripheral and central

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10
Q

What can peripheral chemoreceptors detecting changes in pO2/pCO2/pH be found and what nerves carry the impulses to the brainstem respiratory centre?

A
  • Carotid bodies
    • Glossopharyngeal nerves (IX)
  • Aortic bodies
    • Vagus nerves (X)
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11
Q

What changes in the blood pO2 do peripheral chemoreceptors detect and what changes do the bring about? (Carotid and aortic bodies)

A
  • Changes detected: Respond to large falls in pO2
  • Changes made: Increase tidal volume, rate of respiration, direct more blood to brain and kidneys, increased pumping of blood by the heart

(Respiratory drive from hypoxia remains in persitent hypoxia)

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12
Q

What changes in the blood pCO2 and pH ​do peripheral chemoreceptors detect and what changes do the bring about? (Carotid and aortic bodies)

A
  • Changes detected:
    • Directly activated by changes in pH
    • (respond to LARGE changes in pCO2)
  • Changes made:
    • Low pH: increased respiratory rate and tidal volume
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13
Q

Where can central chemoreceptors be found?

A

Ventral surface of medulla

Exposed to cerebro-spinal fluid

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14
Q

What do the central chemoreceptors respond to and what changes do they bring about?

A

Respond to: rise in arterial pCO2 (pH decrease)

Changes: impulses from chemoreceptors travel to brainstem respiratory centres - change respiration

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15
Q

Why is CSF pH corrected more quickly than blood pH?

A

Small volume of CSF

Lower protein content- overall buffering capacity is less

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16
Q

CSF is separted from the blood by a blood-brain barrier. How is its pH therefore determined?

A

Free passage of CO2 across blood-brain barrier (NOT HCO3-)

pH determined by its own HCO3- conc to dissolved CO2 buffer system

[HCO3-] determined by activity of choroid plexus cells in CSF

17
Q

What happens to the central chemoreceptors if pCO2 remains elevated for any length of time? (eg with lung disease)

A

Choroid plexus cells - reset central chemoreceptors–> no longer sensitive to existing pCO2

(So in long standing hypocapnia- drive from increased ventilation is due to hypoxia (hypoxic drive) via peripheral chemorecpetors)

18
Q

Define hyperventilation.

A

Ventilation increase without change in metabolism

19
Q

Write out the equation that demostrates how pH of the blood is determined by the concentration of dissolved CO2 in the blood and [HCO3-]

A
20
Q

What happens in the body if pH rises above 7.6?

A

Free calcium concentration drops (tetany: condition marked by intermittent muscular spasms)

21
Q

What may cause metabolic alkalosis? How can it be compensated for?

A

Vomiting (loss of protons)

Plasma [HCO3- rises]

Decrease degree of ventilation

22
Q

For info:

A
23
Q

What will happen to total oxygen content of the blood if a normal individual breathes air at twice normal atmospheric pressure?

A
24
Q

Fill in the missing gaps in the table:

A