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Respiratory > Lec 7 - Chemical Control of Breathing > Flashcards

Lec 7 - Chemical Control of Breathing Flashcards

1
Q

What is the pH in the plasmas?

A

7.35 - 7.45

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2
Q

What is the concentration of bicarbonate in the plasma?

A

22 - 26 mmol/L

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3
Q

What is the PaO2?

A

9.3 - 13.3 kPa

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4
Q

What is the PaCO2?

A

4.7 - 6.0 kPa

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5
Q

What is the function of the respiratory system?

A
  1. To maintain oxygen and carbon dioxide partial pressure gradients to optimise transfer.
  2. To regulate pH of the extracellular fluid.
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6
Q

Define hypoxia?

A

Fall in pO2

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7
Q

Define hypocapnia

A

Fall in pCO2

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8
Q

Define hypercapnia

A

Rise in pCO2

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9
Q

Define hyperventilation

A

Ventilation increase without changing metabolism.

  • pO2 will rise.
  • pCO2 will fall.
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10
Q

Define hypoventilation

A

Ventilation decrease without changing metabolism.

  • pO2 will fall.
  • pCO2 will rise.
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11
Q

What happens if pO2 changes without a change in pCO2?

A
  • If pO2 changes without a change in pCO2, correction of pO2 will cause pCO2 to drop.
  • This leads to hypocapnia.
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12
Q

What happens in the carbonic acid-bicarbonate buffer system?

A
  • It is a major buffer system in blood.
  • It is highly effective because the amount of dissolved CO2 is controlled by respiration.
  • In addition the concentration of HCO3- is regulated by the kidneys.
  • pH = pK + log [HCO3-] / [H2CO3-].
  • because H2CO3- is in eqm with CO2 so can be substituted for it.
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13
Q

What is the effect of pCO2 on plasma pH?

A

pH = pK + log ([HCO3-]/(pCO2 x o.23))

  • If [HCO3-} remains unchanged the following happens:
    • If pCO2 increases then pH falls.
    • If pCO2 decreases then pH rises.
  • Small changes in pCO2 lead to large changes in pH.
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14
Q

What happens if plasma pH falls below 7.0?

A
  • enzymes become denatured.
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15
Q

What happens if plasma pH rises above 7.6?

A
  • free calcium concentration drops leading to tetany.
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16
Q

How does hypoventilation influence plasma pH?

A

It leads to an increase in pCO2

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17
Q

How does hypercapnia influence plasma pH?

A

It leads to a fall in plasma pH.

—> respiratory acidosis.

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18
Q

How does hyperventilation influence plasma pH?

A

It leads to a decrease in pCO2.

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19
Q

How does hypocapnia influence plasma pH?

A

It leads to a rise in plasma pH.

—> Respiratory alkalosis

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20
Q

What does plasma pH depend upon?

A

It depends upon the ratio of [HCO3-] to pCO2

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21
Q

What compensates changes in pCO2?

A

Changes in pCO2 can be compensated for by changes in [HCO3]-

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22
Q

What controls the concentration of HCO3-?

A

The kidney

23
Q

How is respiratory acidosis compensated for?

A

It is compensated by the kidneys increasing the concentration of HCO3-.

24
Q

How is respiratory alkalosis compensated for?

A

It is compensated by the kidneys decreasing the concentration of HCO3-.

25
Q

What happens in metabolic acidosis?

A
  • If the tissue produces acid, it reacts with HCO3-.

- The fall in [HCO3-] leads to a fall in pH.

26
Q

How is metabolic acidosis compensated for?

A
  1. Compensated for by changing ventilation.
  2. Increased ventilation lowers pCO2.
  3. This restores pH towards normal.
27
Q

What happens in metabolic alkalosis?

A
  • If plasma [HCO3-] rises e.g after vomiting.

- Plasma pH will rise.

28
Q

How is metabolic alkalosis compensated for?

A

It can be compensated by decreasing ventilation.

29
Q

How are metabolic changes in pH compensated for?

A

By breathing ( ventilation)

30
Q

How are respiratory driven changes in pH compensated for?

A

By the kidney, so by [HCO3-} changes

31
Q

Describe the changes in pH, pCO2 and HCO3- that indicates respiratory acidosis?

A
  1. pH decreased
  2. pCO2 increased
  3. HCO3-, normal or increased.
32
Q

Describe the changes in pH, pCO2 and HCO3- that indicates respiratory alkalosis?

A
  1. pH increased.
  2. pCO2 decreased
  3. HCO3-, normal or decreased.
33
Q

Describe the changes in pH, pCO2 and HCO3- that indicates metabolic acidosis?

A
  1. pH decreased
  2. pCO2, normal or decreased.
  3. HCO3- decreased
34
Q

Describe the changes in pH, pCO2 and HCO3- that indicates metabolic alkalosis?

A
  1. pH increased
  2. pCO2, normal or increased.
  3. HCO3- increased.
35
Q

What do central chemoreceptors detect?

A

H+ ions

36
Q

What do peripheral chemoreceptors detect?

A

O2, CO2, H+

37
Q

What do pulmonary receptors detect?

A

stretch

38
Q

What do joint and muscle receptors detect?

A

stretch and tension

39
Q

What are the effectors in inspiration?

A
  • external intercostals

- Accessory muscles

40
Q

What are the effectors in expiration?

A
  • Internal intercostals

- Abdominal muscles

41
Q

What are peripheral chemoreceptors?

A

carotid and aortic bodies.

42
Q

What do large falls in pO2 stimulate?

A
  1. Increased breathing.
  2. changes in heart rate.
  3. changes in blood flow distribution such as increasing flow to brain and kidneys.
43
Q

Compare the sensitivity to pCO2 of peripheral and central chemoreceptors.

A
  • peripheral chemoreceptors will detect changes but are relatively insensitive to pCO2.
  • chemical chemoreceptors in the medulla of the brain are much more sensitive to pCO2.
44
Q

What does the blood-brain barrier do?

A

It prevents H+ and HCO3- from affecting brain ECF or CSF.

  • It also separates CSF from blood.
  • only gases can cross the blood brain barrier.
  • It is impermeable to HCO3-.
45
Q

What stimulates the acidification of central chemoreceptor neurons?

A

acidification of CSF and ECF stimulates central chemoreceptor neurons.

46
Q

What do central chemoreceptors do?

A
  1. detect changes in arterial pCO2.
  2. Small rises in pCO2 increase ventilation.
  3. Small falls in pCO2 decrease ventilation.
  4. It also responds to changes in the pH of cerebro-spinal fluid (CSF)
47
Q

Describe the negative feedback control of breathing?

A
  1. There Is an increase in pCO2.
  2. This increase is detected by central chemoreceptors.
  3. This stimulates breathing.
  4. Blows off CO2.
  5. pCO2 returns to normal then repeat loop.
48
Q

What controls the HCO3- concentration in CSF?

A

Controlled by choroid plexus cells.

49
Q

What determines pCO2 in CSF?

A

Arterial pCO2.

50
Q

What determine CSF pH and how is it affected by pCO2?

A
  • determined by ratio of [HCO3-] to pCO2.
  • falls in pCO2 leads to rises in CSF pH.
  • rise in pCO2 leads to falls in CSF pH.
  • but persisting changes in pH are corrected by choroid plexus cells which change [HCO3-]
51
Q

What do the choroid plexus cells do?

A

Their role is in secretion and excretion of bicarbonate.

52
Q

What happens when there is a fall in CSF pH?

A
  1. The fall in CSF pH is detected by central chemoreceptors.
  2. It drives increased ventilation.
  3. This lowers pCO2, which restores CSF pH.
53
Q

What happens in persisting hypoxia?

A
  1. Hypoxia is detected by peripheral chemoreceptors.
  2. This increases ventilation.
  3. But pCO2 will fall further, hence there is a decrease in ventilation.
  4. So CSF composition compensates for the altered pCO2.
  5. Choroid plexus cells selectively add H+ or HCO3- into CSF.
  6. Central chemoreceptors accept the pCO2 as normal.

Respiratory (9 decks)

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