Respiration: gas transport

Question 1

Along which gradient do gases move?

Answer 1

down their pressure gradient

Question 2

What is the partial pressure of oxygen in oxygenated blood leaving lungs?

Answer 2

pO2 = 95-100

Question 3

What is the partial pressure of carbon dioxide in oxygenated blood?

Answer 3

pCO2 = 40

Question 4

What is the partial pressure of oxygen in deoxygenated blood returning to the lungs?

Answer 4

pO2 = 40

Question 5

What is the partial pressure of carbon dioxide in deoxygenated blood returning to the lungs?

Answer 5

pCO2 = 45

Question 6

Describe the movement of gases in the pulmonary circuit

Answer 6

O2 moves down its pressure gradient from the alveolar air (pO2=100) into the venous blood (pO2=40). CO2 moves down its pressure gradient from the blood (pCO2=45) to the alveoli (pCO2=40)

Question 7

Describe the movement of gases in the systemic circuit

Answer 7

Oxygen moves down its pressure gradient from the arterial blood (pO2=95) into the tissues (pO2=40), carbon dioxide moves down its pressure gradient from tissues (pCO2=45) to blood (pCO2=40)

Question 8

Which gas has the steeper pressure gradient?

Answer 8

O2

Question 9

How do similar volumes of CO2 and O2 move each minute?

Answer 9

although O2 has a steeper pressure gradient, CO2 is more diffusible

Question 10

Which body systems work together to transport oxygen from the lungs into tissues and carbon dioxide from tissues to lungs?

Answer 10

respiratory and circulatory systems

Question 11

How do gases move?

Answer 11

diffusion

Question 12

Which properties of the respiratory and circulatory systems facilitate gas diffusion?

Answer 12

1. large SA for gas exchange (100m2 alveolar sacs)
2. large partial pressure gradients
3. gases with advantageous diffusion properties
4. specialised O2 and CO2 transport mechanisms

Question 13

How to calculate the partial pressure of a gas

Answer 13

fraction of gas x barometric pressure

Question 14

What are the 2 forms oxygen is transported in?

Answer 14

dissolved and bound to haemoglobin (Hb)

Question 15

How is dissolved O2 measured?

Answer 15

measured clinically in an arterial blood sample (PaO2) usually using radial artery

Question 16

What is the amount of dissolved O2 in blood proportional to?

Answer 16

partial pressure of oxygen

Question 17

How many ml of oxygen is dissolved in 100ml of blood per mmHg?

Answer 17

per mmHg, there is 0.003ml O2/100ml blood

Question 18

How much oxygen is dissolved in arterial blood?

Answer 18

PaO2 = 100mmHg therefore 0.003 x 100 = 0.3ml O2/100ml = 3ml O2/L of blood

Question 19

At rest example of inadequacy of only dissolved O2

Answer 19

CO at rest = 5 L/min
3ml O2/L x 5 = 15 ml O2
But requirement is 250ml O2/min

Question 20

Strenuous exercise example of inadequacy of relying on dissolved O2 transport

Answer 20

CO = 30 L/min
3ml O2/L x 30 = 90 ml O2
But requirement is 5000ml O2/min

Question 21

What is the major transport molecule for O2?

Answer 21

Haemoglobin

Question 22

Structure of haemoglobin

Answer 22

4 haem groups (iron porphyrin compounds) joined to globin protein (2 alpha, 2 beta polypeptide chains)

Question 23

Where is the oxygen binding site in haemoglobin?

Answer 23

iron in the reduced ferrous form (Fe3+) found in each haem group

Question 24

How many O2 molecules can one Hb molecule carry?

Answer 24

4 (4 haem groups)

Question 25

How many Hb molecules per red blood cell?

Answer 25

280 million

Question 26

How fast does binding/dissociation of oxygen with Hb occur?

Answer 26

milliseconds (RBCs only in pulmonary capillaries for 1s)

Question 27

What does the oxyhaemoglobin dissociation curve illustrate?

Answer 27

the relationship between pO2 in blood and number of O2 molecules bound to Hb (% Hb saturation)

Question 28

Describe the shape of the oxyhaemoglobin dissociation curve

Answer 28

s-shaped with a flat portion from pO2 100 to 60, and a steep portion

Question 29

Describe the clinical significance of the flat portion of the oxyhaemoglobin dissociation curve

Answer 29

drop in pO2 from 100 to 60mmHg causes a minimal reduction in Hb saturation (ensures not all O2 molecules are released immediately)

Question 30

What is the clinical significance of the steep portion of the oxyhaemoglobin dissociation curve?

Answer 30

a small change in pO2 (40 to 20mmHg - venous pO2) results in a large amount of O2 being released from Hb

Question 31

Which factors can affect the oxyhaemoglobin dissociation curve?

Answer 31

pH, temperature, pCO2

Question 32

What is the optimal pH and temperature of blood?

Answer 32

pH 7.4 and 38 degrees C

Question 33

What is the effect of a decreased pH on oxyhaemoglobin dissociation curve?

Answer 33

decreased pH shifts the curve to the right (lower % Hb saturation for given pO2)

Question 34

What is the effect of an increased temperature on the oxyhaemoglobin dissociation curve?

Answer 34

shifts curve to the right (lower % Hb saturation for given pO2)

Question 35

Define oxygen saturation (SaO2)

Answer 35

the amount of O2 bound to Hb relative to the maximal amount that can bind

Question 36

What is meant if there is 100% oxygen saturation?

Answer 36

all haem groups of all Hb molecules are fully saturated with O2

Question 37

How much oxygen can bind to 1g Hb?

Answer 37

1g Hb combines with 1.39ml O2

Question 38

How much Hb is in 1L of blood?

Answer 38

~150g Hb/L

Question 39

What is the total O2 capacity that can be carried in 1L of blood?

Answer 39

bound to Hb: 150 x 1.39 = 208 ml O2/L dissolved: 3 ml O2/L total = 211 ml O2/L

Question 40

How can O2 saturation be measured?

Answer 40

using pulse oximeters

Question 41

How do pulse oximeters measure O2 saturation?

Answer 41

measures the ratio of absorption of red and infrared light by oxyHb and deoxyHb

Question 42

How much CO2 is produced at rest?

Answer 42

200 ml CO2 / min

Question 43

For every 100 molecules of O2 entering the blood, how many CO2 molecules are expired by the lungs?

Answer 43

80 molecules of CO2 expired for every 100 O2 entering

Question 44

What term describes the ratio of expired CO2 to O2 uptake?

Answer 44

Respiratory Exchange Ratio

Question 45

What is the respiratory exchange ratio at rest?

Answer 45

0.8 (80 CO2 to 100 O2)

Question 46

In what forms can CO2 be transported?

Answer 46

1. 7% dissolved in plasma 2. 23% bound to Hb 3. 70% converted to bicarbonate

Question 47

What molecule is formed when CO2 binds to haemoglobin?

Answer 47

carbaminohaemoglobin

Question 48

How is carbon dioxide converted to bicarbonate?

Answer 48

CO2 + H2O converted to H2CO3 by carbonic anhydrase. H2CO3 -> HCO3- (Cl- shift) + H+ (removed by Hb buffering)

Question 49

What is the equation for the formation of bicarbonate from CO2?

Answer 49

CO2 + H2O -> H2CO3 -> H+ + HCO3 -

Question 50

What determines the direction and speed of the CO2/HCO3- reaction?

Answer 50

concentration gradients

Question 51

Where is CO2 converted to HCO3 - ?

Answer 51

in systemic capillaries - CO2 produced by tissues and diffuses into blood

Question 52

Where is HCO3 - converted to CO2 (leftwards reaction)?

Answer 52

in pulmonary capillaries - CO2 expelled into alveoli

Question 53

Function of CO2 to HCO3 - pathway

Answer 53

regulates H+ ions and maintains acid-base balance in body

Question 54

How can bicarbonate act as a buffer?

Answer 54

HCO3 - + H+ -> H2CO3 changes in bicarbonate concentrations can stabilise the pH as concentrations of HCO3-, H+ and CO2 are linked.

Question 55

Henderson Hasselbach equation

Answer 55

pH = pKa + log10 [base]/[acid]

Question 56

How can blood pH be calculated using the Henderson Hasselbach equation?

Answer 56

pH = pKa + log10 [HCO3-]/pCO2

Question 57

How can blood pH (acidity) be regulated?

Answer 57

using ventilation to adjust pCO2 or using kidneys to regulate bicarbonate concentration