3. Gas Transport and Exchange

Question 1

What is Dalton’s Law?

Answer 1

Partial pressure of a gas mixture is equal to the sum of the partial pressures of gases in the mixture

Question 2

What is Fick’s law?

Answer 2

Molecules diffuse from regions of high conc to regions of low conc at a rate proportional to the concentration gradient, the exchange surface area and the diffusion capacity of the gas, and inversely proportional to the thickness of the exchange surface

Question 3

What is Henry’s Law?

Answer 3

At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid

Question 4

What is Boyle’s Law?

Answer 4

At a constant temperature, volume is inversely proportional to pressure

Question 5

What is Charle’s Law?

Answer 5

At a constant pressure, volume is directly proportional to temperature

Question 6

If the patient has a diffusion problem what must be done?

Answer 6

Oxygen therapy: Increase the oxygen given - essentially making the diffusion gradient steeper

Question 7

With altitude what happens with the gases?

Answer 7

The pressure of the atmosphere decreases but the proportions of the gases remains the same

Question 8

How many kPa of oxygen is in dry air?

Answer 8

21.3 kPa

Question 9

From dry air through the conducting airways how does the air change?

Answer 9

There is a slight reduction in pO2 and increase in pH20

Question 10

How many kPa of of oxygen is in the conducting airways?

Answer 10

20 kPa

Question 11

How many kPa of H2O is in the conducting airways?

Answer 11

6.3 kPa

Question 12

Why is there an increase in the kPa H2O?

Answer 12

Because dry air becomes warmed, humidified, slowed and mixed as it passes down the respiratory tree

Question 13

How many kPa of oxygen is in the respiratory airways?

Answer 13

13.5 kPa - this is 100% saturation

Question 14

What is the solubility of oxygen?

Answer 14

You can only dissolve 17 mL of oxygen in your body at 0.34 mL/dL

Question 15

What is the human oxygen consumption at rest?

Answer 15

250 mL/min

Question 16

What is the structure of haemoglobin?

Answer 16

Tetramer - 2 alpha and 2 beta chains, represented as HbA. Each chain has as a ferrous iron ion (Fe2+) which binds 1 molecule of O2.

Question 17

What chains are in HbA2?

Answer 17

2 alpha and 2 delta chains

Question 18

How many percent of haemoglobin does HbA2 make up?

Answer 18

2%

Question 19

What chains are in foetal haemoglobin (HbF)?

Answer 19

2 alpha chains and 2 gamma chain

Question 20

Describe the affinity to oxygen for haemoglobin?

Answer 20

Sigmoid shape - When there is no oxygen bound there is a low affinity. However when the first oxygen binds there is a conformational change increasing its affinity to oxygen.

Question 21

When oxygen binds to haemoglobin how does the middle change?

Answer 21

It becomes a binding site for 2,3-DPG

Question 22

What is 2,3-DPG a measure of?

Answer 22

It is reflective of metabolism. The more ATP produced the more 2,3-DPG produced

Question 23

What is the function of 2,3-DPG?

Answer 23

It is used to squeeze out the oxygen - decreases haemoglobins affinity for oxygen.

Question 24

Define allosteric

Answer 24

It will change shape depending on what is bound or not bound

Question 25

Define cooperativity

Answer 25

It will change its shape and affinity based on how much oxygen is bound

Question 26

What does a high partial pressure of oxygen mean?

Answer 26

It means more oxygen will be dissolved

Question 27

What is shape of the oxygen dissociation curve?

Answer 27

sigmoid curve

Question 28

What is the oxygen saturation of haemoglobin in alveolar PO2/pulmonary system?

Answer 28

It is effectively 100% across a big range of PO2

Question 29

What is the oxygen saturation of haemoglobin in the tissues/systemic system?

Answer 29

In the tissues it can go from 76% to 7% saturated - high unloading capacity

Question 30

Define P50

Answer 30

The partial pressure of oxygen when haemoglobin is 50% saturated

Question 31

What is P50 good at estimating?

Answer 31

The shape of ODC

Question 32

What is the meaning behind an oxygen dissociation curve shifted to the right?

Answer 32

This suggests exercise - decreased affinity to oxygen so increased unloading

Question 33

What happens when you exercise?

Answer 33

1) Increase in temperature 2) Acidosis (due to production of lactic acid and excess CO2) 3) Hypercapnia 4) Increase in 2,3-DPG

Question 34

Define hypercapnia

Answer 34

Elevated CO2 because there is more cellular metabolism

Question 35

What are the responses when the ODC shifts to the left?

Answer 35

Opposite of when it shifts to the right

Question 36

What situation would cause the ODC shift downwards?

Answer 36

Anaemic - there is just a lower haemoglobin concentration hence lower amount of oxygen in the blood. However the saturation is the same

Question 37

Less haemoglobin =

Answer 37

Lower oxygen carrying capacity

Question 38

Define polycythaemia

Answer 38

increase in the packed cell volume (haematocrit) in the blood - it could be due to an increase in the number of RBC

Question 39

What situation would cause the ODC shift upwards?

Answer 39

Polycythaemia - increased oxygen carrying capacity

Question 40

What affect does CO have on the ODC?

Answer 40

Downards and leftwards shift

Question 41

What does CO do to haemoglobin?

Answer 41

It decreases haemoglobin's capacity for oxygen and increases its affinity.

Question 42

How does CO increase haemoglobins affinity for oxygen?

Answer 42

When two of the chains are bound to O2 and the two are bound CO, The two chains bound to O2 will hold the oxygen more tightly

Question 43

What is myoglobin's effect towards O2?

Answer 43

It has a much greater affinity than adult HbA.

Question 44

What is the function of myoglobin?

Answer 44

It extracts oxygen circulating in the blood and stores it

Question 45

What is the function of foetal haemoglobin?

Answer 45

It has a high affinity so it can steal oxygen from the mother's blood

Question 46

What the shape of myoglobins ODC?

Answer 46

hyperbolic

Question 47

What it the percentage of oxygen saturation arriving at the alveoli?

Answer 47

The blood arriving is 75% oxygen bound - not deoxygenated

Question 48

What is the kPa of O2 arriving at the exchange surface of the alveoli in the mixed venous blood?

Answer 48

5.3 kPa

Question 49

How does oxygen move from the blood into the RBC?

Answer 49

By diffusion. The plasma conc of oxygen is higher than the intraerthrocytic partial pressure of O2

Question 50

What is the percentage saturation of blood when it reaches the tissues?

Answer 50

97%

Question 51

Why is percentage saturation of blood not 100% by the time it reaches the tissues from the lungs?

Answer 51

It is diluted by bronchial circulation

Question 52

How many circulations does the pulmonary system have?

Answer 52

2

Question 53

What changes take place at the tissue?

Answer 53

The concentration of oxygen decreases from 20.3 - 15.1 mL/dL The saturation of oxygen decreases from 97% to 75%

Question 54

Define oxygen flux

Answer 54

The overall amount of oxygen being deposited

Question 55

What is the oxygen flux in the tissues?

Answer 55

-5 mL/dL this is the amount of oxygen deposited at the tissues

Question 56

How many decilitres are in the body?

Answer 56

50 dL

Question 57

What is the resting volume of oxygen consumed?

Answer 57

250 mL of oxygen per minute

Question 58

Where does CO2 diffuse into?

Answer 58

The blood stream

Question 59

How soluble is CO2?

Answer 59

It is more soluble than O2

Question 60

What does CO2 react with in the blood?

Answer 60

Water to form carbonic acid H2CO3

Question 61

What does carbonic acid produced in the blood dissociate into?

Answer 61

H+ and HCO3- | This is slow reaction - no enzymes

Question 62

What catalyses the reaction converting CO2 to H2CO3 in RBC?

Answer 62

Carbonic anhydrase

Question 63

How many times faster does the enzyme in RBC catalyse the reaction?

Answer 63

5000 times greater

Question 64

How does bicarbonate produced in the RBC leave and go into the plasma?

Answer 64

Via AE1 transporters which moves a chloride ion in

Question 65

What is chloride shift?

Answer 65

The movement of Cl- into the RBC while exchanging for HCO3-. Electroneutrality must be maintained across the membrane

Question 66

What does the Cl- ion bring with it when it moves into the RBC?

Answer 66

Water, which prevents the cell from dehydrating and getting smaller

Question 67

How/where does carbaminohaemoglobin form?

Answer 67

When CO2 binds to the amino end of proteins.

Question 68

How does pH within the RBC maintained with the production of H+ ions?

Answer 68

The proteins make good bufffers

Question 69

How does the CO2 flux change from arterial and venous blood?

Answer 69

48 to 52mL/dL

Question 70

How many ml of CO2 is produced every minute?

Answer 70

200 mL

Question 71

How many ml of oxygen is consumed ever minute?

Answer 71

250mL

Question 72

Define respiratory membrane

Answer 72

areas where the alveolar cells and endothelial cells of the capillaries are close enough for exchange to take place

Question 73

Define pulmonary transit time

Answer 73

This is time where gas exchange can takes place

Question 74

How long is the pulmonary transit time?

Answer 74

0.75s however gas exchange will already been completed in 0.25s

Question 75

Define Haldane effect

Answer 75

Describes the amount of CO2 that binds to the amine end of the haemoglobin protein changes depending on how much oxygen is bound. Allosteric effect.

Question 76

Will CO2 bind to haemoglobin when O2 saturation is 100%?

Answer 76

No, when it starts to unload O2 it becomes more receptive to CO2

Question 77

Which part of the lung is least perfused and why?

Answer 77

The apex because of the resistance of gravity

Question 78

Which part of the lung is better ventilated?

Answer 78

Bottom of the lung compared to the top