Session 5

Question 1

Define Hypercapnia

Answer 1

An increase in pCO2

Question 2

Define Hypocapnia

Answer 2

A decrease in pCO2

Question 3

Below what value is classified as Hypoxia?

Answer 3

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

Question 4

Define Hyperventilation

Answer 4

Breathing more than you need to

Question 5

Define Hypoventilation

Answer 5

Breathing less than you need to

Question 6

What happens to gas levels in Hyperventilation?

Answer 6

pCO2 falls

pO2 rises

Question 7

What happens to has levels in Hypoventilation?

Answer 7

pCO2 rises

pO2 falls

Question 8

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

Answer 8

Because correcting the Hypoxia will cause Hypocapnia

Question 9

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

Answer 9

If pCO2 rises, pH drops

If pCO2 drops, pH rises

Question 10

What happens if plasma pH drops below 7?

Answer 10

K+ rises

Enzymes become denatured

Question 11

What happens if plasma pH rises above 7.6?

Answer 11

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

Question 12

Why do you have respiratory acidosis?

Answer 12

Hypoventilation occurs leading to Hypercapnia which causes plasma pH to fall

Question 13

Why do you have respiratory alkalosis?

Answer 13

Hyperventilation occurs leading to Hypocapnia which causes plasma pH to rise

Question 14

What does plasma pH depend on?

Answer 14

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

Question 15

What controls HCO3-?

Answer 15

The kidneys

Question 16

What compensates for respiratory alkalosis/acidosis?

Answer 16

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

Question 17

What is Metabolic acidosis?

Answer 17

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

Question 18

How is Metabolic acidosis compensated for?

Answer 18

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

Question 19

What is Metabolic alkalosis?

Answer 19

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.

Question 20

How is Metabolic alkalosis compensated for?

Answer 20

Decreased ventilation

Question 21

How are respiratory changes in pH compensated for?

Answer 21

By the kidney

Question 22

How are metabolic changes in pH compensated for?

Answer 22

By breathing

Question 23

What determines breathing?

Answer 23

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

Question 24

What monitors arterial pO2?

Answer 24

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

Question 25

What does a large decrease in pO2 stimulate?

Answer 25

Increased breathing
Changes in heart rate
Blood diversion to the brain

Question 26

What senses changes in pCO2?

Answer 26

Central chemoreceptors in the medulla of the brain

Peripheral chemoreceptors too, but these are insensitive

Question 27

How do central chemoreceptors detect changes in pCO2?

Answer 27

They respond to changes in pH of the Cerebrospinal fluid

Question 28

How do the central chemoreceptors respond if pCO2 is too high?

Answer 28

They increase ventilation

Question 29

How do the central chemoreceptors respond if pCO2 is too low?

Answer 29

They decrease ventilation

Question 30

What happens if there is a short term increase in pCO2?

Answer 30

There is an increase in pH of the Cerebrospinal fluid which causes an increase in breathing

Question 31

What happens if there is a long term increase in pCO2?

Answer 31

The Choroid plexus alters HCO3- concentration. This takes a few hours