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Human Epithelial Biology > O2 and CO2 Transfer Between Alveolus, Blood and Tissue > Flashcards

O2 and CO2 Transfer Between Alveolus, Blood and Tissue Flashcards

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1
Q

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

A

Physical

Chemical

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2
Q

How is O2 carried physically in the blood?

A 
plasma soluble (2%)
0.3ml O2/100ml blood
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3
Q

How is O2 carried chemically in the blood?

A

O2 bound to hemoglobin (98%)

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4
Q

How much O2 does Hb bind?

A

1.34ml

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5
Q

How much hemoglobin is there per 100ml blood?

A

15g

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6
Q

What is the O2 carrying capacity of Hb?

A

20mls O2/100ml

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7
Q

What is the total arterial content of O2?

A

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

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8
Q

What is the total venous O2 content?

A

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

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9
Q

How are SaO2 calculated?

A

Oxyhemoglobin/O2 carrying capacity of Hb

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10
Q

What is the problem with SaO2?

A

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

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11
Q

What is the P50 value on the oxygen dissociation curve?

A

the PO2 required for half maximal Hb saturation

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12
Q

What saturation does venous blood enter the alveolus?

A

75%

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13
Q

What does the arterial plateau phase ensure?

A

maximal HbO2 saturation even if alveolar PO2 is below normal

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14
Q

What does the steep phase of the curve favour?

A

offload of arterial oxygen to tissues

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15
Q

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

A

increased Hb-O2 affinity and reduced offloading to tissue

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16
Q

Where might a left shift in the ODC be seen?

A

fetal Hb

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17
Q

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

A

decreased Hb-O2 affinity and raised offloading to tissues

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18
Q

Where might a right shift in the ODC be seen?

A

high altitude

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19
Q

What may cause a right shit in the ODC?

A

stressors such as acidosis, fever and hypoxia

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20
Q

Describe the structure of hemoglobin

A

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

21
Q

What alters the affinity of hemoglobin for O2?

A

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

22
Q

What does hemoglobin require for each 2O2 released?

A

H+ ion

23
Q

What interaction is pH and O2 sensitive?

A

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

24
Q

What happens to the interaction a physiological pH?

A

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

25
Q

What happens to the interaction in acidosis?

A

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

26
Q

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

A

production of carbonic acid in red cell

Carbamate reaction at the N-terminal amino groups on the Hb a-subunit

27
Q

What is the reaction produced for carbonic acid?

A

CO2 + H2O -> H2CO3 -> HCO3 + H

28
Q

What is the reaction produced for carbamate reaction?

A

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

29
Q

What is the overall effect of increased blood pCO2?

A

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

30
Q

What are the other factors affecting O2 transport?

A

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

31
Q

What PO2 does fetal development occur at?

A

30mmHg

32
Q

What ODC does the fetus have compared with the mother?

A

left shifted ODC - so high affinity for O2

33
Q

How does the fetus allow for O2 off-loading?

A

very low PO2 at tissues

34
Q

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

A

y subunit

replaced at birth by bHb

35
Q

What are the physical forms of CO2 in the blood?

A

Soluble CO2 5%

Bicarbonate ion 90%

36
Q

What is the chemical form of CO2 in the blood?

A

carbamino hemoglobin

37
Q

What is the amount of CO2 exhaled?

A

4ml CO2/100ml blood

38
Q

How is the plasma pH buffered by the red cell?

A

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

39
Q

What is the Haldane effect?

A

Where deoxygenation of blood improves carriage of CO2

40
Q

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

A

CO2 dissolves into plasma and red cell along partial pressure gradient

41
Q

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

A

low tissue O2 favours CO2 carriage by blood - HALDANE

42
Q

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

A

Carbamate reaction reduces HbO2 affinity - BOHR

43
Q

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

A

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

44
Q

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

A

Increased H in RBC reduces HbO2 affinity - BOHR

45
Q

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

A

O2 dissolves into plasma along partial pressure gradient

46
Q

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

A

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

47
Q

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

A

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

48
Q

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

A

Movement of CO2 out of RBC increases HCO3 uptake

49
Q

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

A

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

Human Epithelial Biology (20 decks)

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