Carbon Dioxide In Blood And Chemical Control Of Breathing

Question 1

How much more carbon dioxide is there in arterial blood than oxygen?

Answer 1

2.5 x

Question 2

What is the total content of carbon dioxide in arterial blood?

Answer 2

21 mmol/L

Question 3

What is the total content of oxygen in arterial blood?

Answer 3

8.9 mmol/L

Question 4

What range must we keep arterial blood pH between?

Answer 4

7.35 - 7.45

Question 5

How do we work out the concentration of carbon dioxide dissolved?

Answer 5

Solubility of CO2 x partial pressure CO2

Question 6

What is the solubility factor of carbon dioxide at 37’C?

Answer 6

0.23 mmol/L/kPa

Question 7

How does carbon dioxide reaction with water?

Answer 7

CO2 and water reacts to form carbonic acid (H2CO3)
Very quickly dissociates to form H+ and HCO3-
Reversible reaction

Question 8

What does the pH of the blood depend on?

Answer 8

CO2 dissolved that reacts to form H+

Question 9

What is the partial pressure of CO2 in the alveoli determined by?

Answer 9

Rate of breathing

Question 10

What happens to the partial pressure of CO2 if we hyperventilate?

Answer 10

Decreases

Question 11

What happens to the partial pressure of CO2 if we hypoventilate?

Answer 11

PCO2 increases

Question 12

What is the normal concentration of HCO3- in the plasma?

Answer 12

25 mmol/L

Question 13

What is the cation mostly associated with HCO3-?

Answer 13

Na+

Question 14

How does a high HCO3- affect CO2?

Answer 14

Pushes the equation to the left
Prevents nearly all of the CO2 from reaction
Therefore plasma is alkaline

Question 15

What is the equation for calculating pH from pCO2 and HCO3-?

Answer 15

Henderson-Hasselbach Equation

pH = pK + log ([HCO3-] / (pCO2 x 0.23) )

pK = constant 6.1 at body temperature

Question 16

What is the normal ratio of HCO3- to CO2?

Answer 16

20:1

Question 17

Which enzyme speeds up the reaction of CO2 and water?

Answer 17

Carbonic anhydrase (CA)
In RBCs

Question 18

What happens to the products of the CO2 reaction in a RBC?

Answer 18

H+ ions bind to negatively charged Hb

Chloride bicarbonate exchanger (antiporter) transports HCO3- out of RBCs

Question 19

Where is the concentration of HCO3- in the body controlled?

Answer 19

Kidneys

Question 20

What happens when the body produces acids?

Answer 20

React with HCO3- to produce CO2

Removed via breathing

Question 21

What happens when venous blood arrives at the lungs?

Answer 21

Hb picks up oxygen - goes into R state
Hb gives up the extra H+ it took on in the tissues
H+ reacts with HCO3- to form CO2 which is breathed out

Question 22

Describe the formation of carbamino compounds

Answer 22

Carbon dioxide binds directly to proteins
Carbon dioxide binds directly to amine groups on globin of Hb
More carbamino compounds formed at the tissues because partial pressure of carbon dioxide higher

Question 23

Name the 3 forms in which carbon dioxide is transported

Answer 23

Dissolved carbon dioxide (10%)
As hydrogen carbonate (60%)
As carbamino compounds (30%)

Question 24

What is the concentration of carbon dioxide in the venous blood?

Answer 24

23 mmol/L

Question 25

What is the partial pressure range for CO2 in the blood?

Answer 25

4.2 - 6.0 kPa

Question 26

What is the partial pressure range for oxygen in the blood?

Answer 26

9.8 - 14.2 kPa

Question 27

What is the reference range for concentration of HCO3- in the blood?

Answer 27

21-29 mmol/L

Question 28

Why can the partial pressure of oxygen drop considerably before saturation is markedly affected?

Answer 28

Plateau at the top of the oxygen-Hb saturation curve

Cooperative binding of Hb

Question 29

How long does the compensation of acidosis or alkalosis take in the kidneys?

Answer 29

Correction to the needed level of HCO3- takes 2-3 days

Question 30

How is metabolic acidosis compensated by changing ventilation?

Answer 30

Increased ventilation
Decreases partial pressure of carbon dioxide
Increases the pH

Question 31

What do central chemoreceptors detect?

Answer 31

H+

Question 32

What do peripheral chemoreceptors detect?

Answer 32

Oxygen
Carbon dioxide
H+

Question 33

Where are peripheral chemoreceptors located?

Answer 33

Carotid and aortic bodies

Question 34

What do large falls in pO2 stimulate?

Answer 34

Increased breathing
Changes in HR
Changes in blood flow distribution

Question 35

What are peripheral chemoreceptors typically insensitive to?

Answer 35

pCO2

Question 36

Where are the central chemoreceptors located?

Answer 36

Medulla of brain

Question 37

What are the central chemoreceptors detecting?

Answer 37

The partial pressure of carbon dioxide

Changes in pH of the CSF

Question 38

What controls the concentration of HCO3- in the CSF?

Answer 38

Choroid plexus cells

Question 39

What is the pCO2 in the CSF determined by?

Answer 39

Arterial pCO2

Question 40

Why does the pH change in the CSF in response to change in pCO2?

Answer 40

HCO3- cannot compensate for the change in pCO2 because the BBB is impermeable to HCO3-
(Persisting changes in pH will be corrected by the choroid plexus cells but takes a long time)

Question 41

What happens when there is an elevated pCO2?

Answer 41

pH decreases 
Detected by the central chemoreceptors 
Increased ventilation 
Decreased pCO2
Restore CSF pH

Question 42

What happens in persisting hypoxia?

Answer 42

Detected by peripheral chemoreceptors
Increased ventilation
(This decreases CO2 which can be bad if a type 2 resp failure)

Question 43

What happens during persisting hypercapnia?

Answer 43

Respiratory acidosis
Decreased pH of CSF
Peripheral and central chemoreceptors increase ventilation