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BS - Respiratory System > Carriage of O2 and CO2 in the Blood > Flashcards

Carriage of O2 and CO2 in the Blood Flashcards

1
Q

What are the 2 main ways in which oxygen is carried in the blood?

A

Dissolved in the blood or combined with haemoglobin

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2
Q

What equation is used to determine the amount of oxygen that dissolves in the blood?

A

volume of oxygen = 0.0232 x pO2

0.29 = 0.0232 x 12.5

By the time the oxygen reaches the alveoli, the pO2 is 12.5 kPa

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3
Q

What equation is used to determine partial pressure?

A

partial pressure = fractional concentration x barometric pressure

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4
Q

What is barometric pressure in the atmosphere?

A

101.3 kPa

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5
Q

How much oxygen is dissolved in one decilitre of blood?

A

0.29 ml of oxygen is dissolved in each 100 ml of blood

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6
Q

In cold water, how does the amount of gas dissolved differ than at 37 degrees?

A

There is more oxygen and CO2 dissolved in cold water

More gas will dissolve at lower temperatures

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7
Q

What is the significance of the value 0.0232 in the equation?

Is it a constant?

A

It describes the solubility of oxygen

Calculations are always at 37oC so it does not change

The value changes if the calculations are worked out at a different temperature

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8
Q

What is oxygen saturation?

A

It describes how much of the haemoglobin in the blood is bound with oxygen, compared to how much haemoglobin there is in total

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9
Q

How is oxygen saturation calculated?

A

Amount of oxyhaemoglobin divided by the total amount of haemoglobin

HbO2 / (HHb + HbO2)

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10
Q 
What do 
SO2
HbO2
HHb
stand for?
A

SO2 - oxygen saturation

HbO2 - oxyhaemoglobin

HHb - deoxyhaemoglobin

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11
Q

What equation is used to determine how much oxygen is being carried by haemoglobin?

A

volume of O2 = SO2 x [Hb] x 1.39

19 = 0.97 x 14 x 1.39

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12
Q

What is the Hüfner constant and what does it describe?

A

1.39

it describes the number of ml of oxygen that each gram of Hb can carry

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13
Q

What is normal haemoglobin concentration?

A

14 grams per 100 ml

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14
Q

How much oxygen is carried by Hb per 100 ml of blood?

A

Hb can carry 19 ml of oxygen per 100 ml of blood

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15
Q

How many amino acids are in each of the 4 polypeptide chains that make up Hb?

A

141 - 146 amino acids per chain

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16
Q

What is the tertiary structure of Hb?

A

A globular structure determined by the order of amino acids in the primary structure

It forms a crevice in which the haem group will sit

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17
Q

What are the 2 forms in which Hb exists?

What does this describe?

A

Relaxed and tense forms

This describes how tightly packed the globin is within the chain

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18
Q

What does Hb act/look like in the relaxed state?

A

The globin is more spread out

The crevices containing the haem group becomes slightly wider

The oxygen can access the haem group more easily

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19
Q

What does Hb act/look like in the tense state?

A

The globin is more tightly condensed

The crevices become too small for the oxygen to fit into easily

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20
Q

What happens upon binding of the first oxygen molecule to Hb?

A

As soon as one molecule of O2 binds to the haem group, the shape of the globin chain changes

This alters how tense the adjacent globin chains are

The globin chains relax a bit more with each O2 that binds

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21
Q

Why does pO2 of the blood have to be high before Hb begins to be oxygenated?

A

The first molecule of oxygen does not bind to the Hb easily

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22
Q

When deoxygenated blood returns to the heart, how saturated is the Hb and why?

A

Hb is still 75% oxygenated

As blood circulates around the body, only 25% of O2 that is bound to Hb is actually consumed

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23
Q

Under normal circumstances, what part of the Hb molecule is used to carry oxygen?

A

Only the final binding site on each Hb molecule

This is the site that works the most efficiently

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24
Q

What happens as partial pressure of oxygen becomes lower?

A

It becomes harder to carry oxygen in the blood

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25
Q

What is meant by the term ‘cooperativity’?

A

The way in which altering the state of one part of the protein affects the other components

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26
Q

What causes the shape of the oxygen dissociation curve?

A

The cooperativity between polypeptide chains in the Hb molecule

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27
Q

What happens at the bottom of the oxygen dissociation curve?

A

It is difficult to get the oxygen to bind to Hb

The partial pressure must be increased significantly before oxygen starts to bind

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28
Q

What happens at the top of the oxygen dissociation curve?

A

All of the oxygen binding sites are occupied and the curve levels off

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29
Q

What does the arterial point on the oxygen dissociation curve show?

A

The saturation of normal arterial blood

Saturation is around 97% and partial pressure of oxygen is 12.5 - 13 kPa

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30
Q

What does the venous point on the oxygen dissociation curve show?

A

The saturation of normal venous blood

Saturation is around 75% and pO2 is 6.3 kPa

31
Q

What is shown by P50 on the oxygen dissociation curve?

A

This is the point on the curve where Hb is 50% saturated

pO2 is normally 3.5 kPa

32
Q

What is the P50 point on the oxygen dissociation curve used for?

A

To see whether a curve is normal or if it has been shifted

33
Q

What 3 factors can cause the oxygen dissociation curve to shift?

A
  1. temperature
  2. pH change (Bohr effect)
  3. 2,3 diphosphoglycerate in the RBC
34
Q

What is 2,3 diphosphoglycerate and how is it produced?

A

It is produced by anaerobic metabolism

It is a signalling mechanism to RBCs to show that there is not enough oxygen being delivered

35
Q

What happens as the oxygen dissociation curve shifts to the right?

A

The further to the right the curve moves, the more easily the Hb will give up oxygen

It will be harder for Hb to take up oxygen in the lung

36
Q

What causes the oxygen dissociation curve to shift to the left?

A

increased pH

decreased temperature

decreased 2,3 DPG

37
Q

What causes the oxygen dissociation curve to shift to the right?

A

decreased pH

increased temperature

increased 2,3 DPG

38
Q

What are the 4 ways in which a Hb molecule may be abnormal?

A
  1. absent globin chain
  2. defective globin chain
  3. defective iron atom
  4. wrong ligand
39
Q

How can an abnormal Hb have an absent globin chain?

A

The globin chains may be absent from an individual’s genes

40
Q

What causes thalassaemia?

A

The gene for one or more of the globin chains is very abnormal

The gene is so abnormal that none on the globin chain is produced

41
Q

What causes alpha thalassaemia?

A

The alpha chain of Hb is not produced

42
Q

What is significant about alpha thalassaemia?

A

Both foetal and adult Hb contain alpha subunits

The foetus often dies before it reaches full development

43
Q

What is the consequence of beta thalassaemia?

A

It is less severe than alpha

Patients will keep foetal Hb for their whole life

44
Q

What causes sickle cell disease?

A

A single amino acid substitution on the beta globin chain which interferes with the interactions of this globin chain with the other subunits

45
Q

What happens when Hb becomes deoxygenated in sickle cell disease?

A

The Hb molecules in the RBCs begin to stick together

This changes the shape of the RBC

46
Q

When does sickling occur in sickle cell disease?

What is significant about this?

A

At low pO2

this is usually when patients develop infections, become hypoxic or cold

47
Q

How may an iron atom become defective in Hb?

A

Fe2+ is oxidised to Fe3+ which does not carry oxygen

48
Q

What happens when Hb contains Fe3+?

What % of Hb in the blood has Fe3+ instead of Fe2+?

A

This creates methaemoglobin which doesn’t carry oxygen

0.5%

49
Q

How is methaemoglobin usually produced?

A

Usually drug-induced

Drugs used to treat leprosy, local anaesthetics

50
Q

How many times more strongly does CO bind to Hb compared to O2?

A

CO binds to Hb 250 times more strongly than oxygen

51
Q

What happens when CO binds to Hb instead of oxygen?

A

The Hb carrying CO is no longer available to carry oxygen

52
Q

What are the main sources of carbon monoxide?

A

Smoking and house fires

53
Q

What is a buffer?

A

A solution that can minimise changes in the free H+ concentration and therefore in pH

54
Q

How is pH calculated?

A

pH = -log [H+]

55
Q

What does a buffer consist of?

A

A weak acid and its base in equilibrium

56
Q

What is the general buffer equation and the equation for carbonic acid?

A

acid H+ + base

H2CO3 H+ + HCO3

57
Q

What happens if H+ ions are added and removed to the buffer system?

A

When H+ is added, the equation shifts to the left to remove some of the added ions

When H+ is removed, the equation shifts to the right as some acid dissociates to increase H+ concentration

58
Q

What is the role of a buffer?

A

It minimises changes in pH

It does NOT correct the pH and make it normal

59
Q

What are the 4 buffer systems in extracellular fluid?

What is their capacity (mmol H+ per L)?

A

bicarbonate - 18

plasma protein - 1.7

haemoglobin - 8

phosphate - 0.3

60
Q

What is the total buffering capacity of the blood?

A

28 mmol H+ per L

61
Q

How do proteins act as buffers?

A

They have carboxyl and amino groups at the end of a chain, which act as buffers

They also have side chains which contain buffers

62
Q

What is the problem with proteins as buffers?

A

Protein molecules are large which means there are not many protein molecules in the blood

63
Q

How does Hb act as an effective buffer?

A

It has more side chains with buffering ability than any other protein

64
Q

What is the main buffer of intracellular fluid?

A

phosphate

65
Q

What are the limits of blood pH and what H+ concentration does this correspond to?

A

Blood pH is tightly controlled between 7.35 and 7.45

[H+] of 35 - 45 mmol/L

66
Q

Why must blood pH be tightly controlled?

A

Most biological functions depend on the activity of proteins

The structure of proteins is very pH dependent

67
Q

What are the 3 ways in which CO2 can be carried in the blood?

A
  1. dissolved in the blood
  2. carbamino compounds
  3. carbonic acid/bicarbonate
68
Q

What determines how much CO2 can dissolve directly in the blood?

A

It is dependent on the pCO2 of the blood and how soluble CO2 is at 37oC

69
Q

At 37oC, how much CO2 is dissolved in the blood?

A

3 ml CO2 dissolved per 100 ml of blood

This is 10 x the amount of oxygen dissolved

70
Q

How does a carbamino compound form?

A

The carbon dioxide molecule is attached to an amino group on an amino acid

71
Q

Where are amino groups found within proteins?

A

The N-terminal group of all proteins and the side chains of lysine and arginine

72
Q

How does Hb form a carbamino compound?

A

Hb has lots of amino acids with NH2 side chains where CO2 can bind

73
Q

How much CO2 is carried in the blood in the form of carbamino compounds?

A

4 ml of CO2 per decilitre of blood

74
Q

How much carbon dioxide is carried in the blood in the form of bicarbonate ions?

A

45 ml of CO2 per decilitre of blood

BS - Respiratory System (20 decks)

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