O2 and CO2 Transfer Between Alveolus, Blood and Tissue

Question 1

What are the two ways oxygen can be carried in the blood?

Answer 1

Physical

Chemical

Question 2

How is O2 carried physically in the blood?

Answer 2

plasma soluble (2%)
0.3ml O2/100ml blood

Question 3

How is O2 carried chemically in the blood?

Answer 3

O2 bound to hemoglobin (98%)

Question 4

How much O2 does Hb bind?

Answer 4

1.34ml

Question 5

How much hemoglobin is there per 100ml blood?

Answer 5

15g

Question 6

What is the O2 carrying capacity of Hb?

Answer 6

20mls O2/100ml

Question 7

What is the total arterial content of O2?

Answer 7

20 + 0.3ml = 20.3 ml O2/100ml blood

Question 8

What is the total venous O2 content?

Answer 8

O2 carrying capacity is 15mls/O2/100mls and plasma soluble 0.28mls
15.28ml O2/100ml blood

Question 9

How are SaO2 calculated?

Answer 9

Oxyhemoglobin/O2 carrying capacity of Hb

Question 10

What is the problem with SaO2?

Answer 10

it can remain the same even if the O2 content of the blood differs i.e. anemia or polycythemia

Question 11

What is the P50 value on the oxygen dissociation curve?

Answer 11

the PO2 required for half maximal Hb saturation

Question 12

What saturation does venous blood enter the alveolus?

Answer 12

75%

Question 13

What does the arterial plateau phase ensure?

Answer 13

maximal HbO2 saturation even if alveolar PO2 is below normal

Question 14

What does the steep phase of the curve favour?

Answer 14

offload of arterial oxygen to tissues

Question 15

What happens when there is a left shift in P50 for the ODC?

Answer 15

increased Hb-O2 affinity and reduced offloading to tissue

Question 16

Where might a left shift in the ODC be seen?

Answer 16

fetal Hb

Question 17

What happens when there is a right shift in P50 for the ODC?

Answer 17

decreased Hb-O2 affinity and raised offloading to tissues

Question 18

Where might a right shift in the ODC be seen?

Answer 18

high altitude

Question 19

What may cause a right shit in the ODC?

Answer 19

stressors such as acidosis, fever and hypoxia

Question 20

Describe the structure of hemoglobin

Answer 20

heterotetramer with 2a and 2b subunits
4 iron binding heme domains
O2 reversibly binds the Fe3+ ions in the centre of the heme ring

Question 21

What alters the affinity of hemoglobin for O2?

Answer 21

CO2
2,3 BPG
interact with charged amino acids between the a and b subunits

Question 22

What does hemoglobin require for each 2O2 released?

Answer 22

H+ ion

Question 23

What interaction is pH and O2 sensitive?

Answer 23

amino terminus of a subunit binds b-carboxyl terminal histidine stabalising Hb structure

Question 24

What happens to the interaction a physiological pH?

Answer 24

O2 binding to heme can release the protons to produce Oxy-Hb

Question 25

What happens to the interaction in acidosis?

Answer 25

decreased pH favours the a-b subunit interaction and reduces the binding of O2 to heme

Question 26

What are the two ways increased blood pCO2 releases O2 from Hb?

Answer 26

production of carbonic acid in red cell | Carbamate reaction at the N-terminal amino groups on the Hb a-subunit

Question 27

What is the reaction produced for carbonic acid?

Answer 27

CO2 + H2O -> H2CO3 -> HCO3 + H

Question 28

What is the reaction produced for carbamate reaction?

Answer 28

CO2 + R-NH2 -> R-NH-COO + H

Question 29

What is the overall effect of increased blood pCO2?

Answer 29

acid stabilisation of a-b B subunits and a low affinity for O2

Question 30

What are the other factors affecting O2 transport?

Answer 30

Carbon monoxide - far greater affinity than O2 - HbCO, causing left shift Anemia - O2 carrying capacity is lowered - shift right

Question 31

What PO2 does fetal development occur at?

Answer 31

30mmHg

Question 32

What ODC does the fetus have compared with the mother?

Answer 32

left shifted ODC - so high affinity for O2

Question 33

How does the fetus allow for O2 off-loading?

Answer 33

very low PO2 at tissues

Question 34

What Hb subunit is expressed during fetal development and when does this change?

Answer 34

y subunit | replaced at birth by bHb

Question 35

What are the physical forms of CO2 in the blood?

Answer 35

Soluble CO2 5% | Bicarbonate ion 90%

Question 36

What is the chemical form of CO2 in the blood?

Answer 36

carbamino hemoglobin

Question 37

What is the amount of CO2 exhaled?

Answer 37

4ml CO2/100ml blood

Question 38

How is the plasma pH buffered by the red cell?

Answer 38

HCO3 moves out of the red cell to maintain CO2 gradient and plasma pH

Question 39

What is the Haldane effect?

Answer 39

Where deoxygenation of blood improves carriage of CO2

Question 40

What is the first stage in CO2 release from tissue and O2 release from the RBC?

Answer 40

CO2 dissolves into plasma and red cell along partial pressure gradient

Question 41

What is the second stage in CO2 release from tissue and O2 release from the RBC?

Answer 41

low tissue O2 favours CO2 carriage by blood - HALDANE

Question 42

What is the third stage in CO2 release from tissue and O2 release from the RBC?

Answer 42

Carbamate reaction reduces HbO2 affinity - BOHR

Question 43

What is the fourth stage in CO2 release from tissue and O2 release from the RBC?

Answer 43

Carbonic anhydrase reaction generates carbonic acid which protonates. HCO3 leaves cel and maintains CO2 gradient

Question 44

What is the final stage in CO2 release from tissue and O2 release from the RBC?

Answer 44

Increased H in RBC reduces HbO2 affinity - BOHR

Question 45

What is the first stage in CO2 release from RBC and O2 release from the Alveolus?

Answer 45

O2 dissolves into plasma along partial pressure gradient

Question 46

What is the second stage in CO2 release from RBC and O2 release from the Alveolus?

Answer 46

High affinity of Hb for O2 reverses carbamation and protonation raising availability of high affinity Hb - BOHR

Question 47

What is the third stage in CO2 release from RBC and O2 release from the Alveolus?

Answer 47

CO2 diffuses into alveolus according to partial pressure gradient. High PO2 reduces CO2 affinity for Hb - HALDANE

Question 48

What is the fourth stage in CO2 release from RBC and O2 release from the Alveolus?

Answer 48

Movement of CO2 out of RBC increases HCO3 uptake

Question 49

What is the final stage in CO2 release from RBC and O2 release from the Alveolus?

Answer 49

Proton release from Hb and increased HCO3 drive reverse carbonic anhydrase reaction and maintain outward CO2 gradient and lower plasma bicarbonate