Session 5 Flashcards

(31 cards)

1
Q

Define Hypercapnia

A

An increase in pCO2

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2
Q

Define Hypocapnia

A

A decrease in pCO2

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3
Q

Below what value is classified as Hypoxia?

A

8kPa - as has to drop to about this before Hb saturation is severely effected

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4
Q

Define Hyperventilation

A

Breathing more than you need to

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5
Q

Define Hypoventilation

A

Breathing less than you need to

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6
Q

What happens to gas levels in Hyperventilation?

A

pCO2 falls

pO2 rises

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7
Q

What happens to has levels in Hypoventilation?

A

pCO2 rises

pO2 falls

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8
Q

Why can you not correct a fall in pO2 by breathing more if pCO2 is the same?

A

Because correcting the Hypoxia will cause Hypocapnia

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9
Q

How do pCO2 effect pH? (When HCO3- is constant)

A

If pCO2 rises, pH drops

If pCO2 drops, pH rises

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10
Q

What happens if plasma pH drops below 7?

A

K+ rises

Enzymes become denatured

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11
Q

What happens if plasma pH rises above 7.6?

A

The free Ca2+ concentration decreases as Ca2+ goes into bones. This causes Tetany

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12
Q

Why do you have respiratory acidosis?

A

Hypoventilation occurs leading to Hypercapnia which causes plasma pH to fall

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13
Q

Why do you have respiratory alkalosis?

A

Hyperventilation occurs leading to Hypocapnia which causes plasma pH to rise

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14
Q

What does plasma pH depend on?

A

The ratio of pCO2 to HCO3-. This means that changes in pCO2 can be compensated for by changes in HCO3-

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15
Q

What controls HCO3-?

A

The kidneys

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16
Q

What compensates for respiratory alkalosis/acidosis?

A

The kidneys, but it takes 2-3 days as it is made and excreted relatively slowly

17
Q

What is Metabolic acidosis?

A

The tissues produce acid which reacts with HCO3-. This decrease in HCO3- leads to a fall in pH

18
Q

How is Metabolic acidosis compensated for?

A

Changing ventilation - Increased ventilation means decreased pCO2 so the pH will be restored to normal

19
Q

What is Metabolic alkalosis?

A

The plasma HCO3- rises (e.g. due to vomiting as H+ in stomach replaced and H+ production has by product of HCO3-) which causes plasma pH to rise.

20
Q

How is Metabolic alkalosis compensated for?

A

Decreased ventilation

21
Q

How are respiratory changes in pH compensated for?

A

By the kidney

22
Q

How are metabolic changes in pH compensated for?

23
Q

What determines breathing?

A

pH (pCO2) then pO2 as O2 doesn’t need to be tightly controlled as long as it is above 8kPa

24
Q

What monitors arterial pO2?

A

Chemoreceptors in the carotid bodies and aortic bodies (They do not work unless the pO2 is very low)

25
What does a large decrease in pO2 stimulate?
Increased breathing Changes in heart rate Blood diversion to the brain
26
What senses changes in pCO2?
Central chemoreceptors in the medulla of the brain | Peripheral chemoreceptors too, but these are insensitive
27
How do central chemoreceptors detect changes in pCO2?
They respond to changes in pH of the Cerebrospinal fluid
28
How do the central chemoreceptors respond if pCO2 is too high?
They increase ventilation
29
How do the central chemoreceptors respond if pCO2 is too low?
They decrease ventilation
30
What happens if there is a short term increase in pCO2?
There is an increase in pH of the Cerebrospinal fluid which causes an increase in breathing
31
What happens if there is a long term increase in pCO2?
The Choroid plexus alters HCO3- concentration. This takes a few hours