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Respiratory System > Week 4 - Oxygen > Flashcards

Week 4 - Oxygen Flashcards

1
Q

What is the solubility of oxygen?

A

Less soluble than carbon dioxide

0.01 mmol/KPa

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2
Q

What is the calculation for the concentration of dissolved oxygen?

A

Solubility X pO2

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3
Q

What is the normal pO2 in the lungs?

A

13.3 kPa

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4
Q

What is the amount of dissolved oxygen at a pO2 of 13.3 kPa?

A

0.13 mmol/L

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5
Q

How much oxygen does the body need?

A

At rest 12 mmol per minute

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6
Q

What features must oxygen carriers have?

A

Reaction needs to be reversible

Oxygen must dissociate at the tissues to supply them

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7
Q

What are the oxygen binding pigments found in the body called?

A

Haemoglobin and myoglobin

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8
Q

Describe the main features of haemoglobin?

A

Present in blood

Tetramer - binds 4 oxygen molecules

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9
Q

What are the main features of myoglobin?

A

Present in muscle cells

Monomer - binds 1 molecule of oxygen

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10
Q

What is a dissociation curve?

A

Plotted bound oxygen against pO2

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11
Q

Why does the curve plateu?

A

The is limited pigment so it saturates

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12
Q

What does the amount of bound oxygen depend on and how is this issue overcome?

A

Depends on amount of pigment

Overcome by expressing saturation as a percentage

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13
Q

Is myoglobin or haemoglobin saturation curve steeper?

A

Myoglobin - saturates at a much lower pO2

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14
Q

Describes the 2 states of haemoglobin?

A

Low affinity T state - difficult for oxygen to bind

High affinity R state - easier for oxygen to bind

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15
Q

How does O2 binding change the state of haemoglobin?

A

When pO2 is low haemoglobin is in T state so its hard for first oxygen molecule to bind
as each molecule binds it becomes more relaxed so each molecule gets easier to bind

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16
Q

What is the shale of a saturation haemoglobin curve?

A

Sigmoidal curve

17
Q

What kPa is haemoglobin saturated above?

A

9-10 kPa

18
Q

What kPa is haemoglobin half saturated at?

A

3.5 - 4

19
Q

If haemoglobin concentration in the blood is 2.2 mmol/L, what should the oxygen content in the blood be?

A

8.8 mmol/L

20
Q

What will happen to the concentration of oxygen in the blood if patient is anaemic?

A

If lungs are functioning ok the pO2 will be normal but the oxygen content will be lower as less bound to haemoglobin as less haemoglobin to bind to

21
Q

What is tissue pO2 dependant on?

A

How metabolically active the tissue is

22
Q

What is the typical pO2 in the tissues?

A

5 kPa

23
Q

Can oxygen be removed from venous blood?

A

Mixed venous blood has been returned from various tissues
Over half oxygen content is still bound
The lower the tissue pO2 the more oxygen will dissociate
Some tissues may be able to remove some oxygen from the venous blood

24
Q

How low can tissue pO2 get?

A

Cant fall below 3 kPa in most tissues as it must remain high enough to drive oxygen diffusion into cells

25
Q

When can oxygen of tissues fall the lowest?

A

When there is a higher capillary density e.g. Heart muscle as it doesn’t have as far to diffuse

26
Q

Describe the Bohr shift effect?

A

pH effects affinity of haemoglobin
In acidic conditions the curve shifts to the right and promotes T state in haemoglobin
Alkaline conditions promotes R state
The pH is lower in the most metabolically active tissues so extra oxygen is given up

27
Q

How does temperature affect the oxygen dissociation curve?

A

Increased temperature shifts curve to the right

Metabolically active tissues have a slightly higher temperature so extra oxygen will be given up

28
Q

How does 2,3-diphosphoglycerate (2,3-BPG) affect the dissociation curves?

A

Contained by normal red blood cells but in anaemia or at altitude the levels increase
This causes the curve to shift to the right which allows more oxygen to be given up to the tissues

29
Q

When might 2,3-BPG levels drop?

A

In store blood due to refrigeration but this is not usually a problem clinically

30
Q

Describe carbon monoxide poisoning?

A

Carbon monoxide reacts with haemoglobin to form COHb

Increases affinity of unaffected subunits for oxygen so they won’t give up at tissues

31
Q

When is carbon monoxide poisoning fatal?

A

When HbCO > 50%

32
Q

What is cyanosis?

A

Bluish colouration due to unsaturated haemoglobin
Deoxygenated haemoglobin is less red than oxygenated
Can be peripheral due to poor circulation or central due to poorly saturated blood in systemic circulation

33
Q

What is pulse oximetry used for?

A

To detect level of haemoglobin saturation in pulsatile arterial blood
Doesn’t say how much haemoglobin is in blood though

34
Q

What can give a better indication of how much haemoglobin is in blood?

A

An arterial blood gas and electrolyte analysis

Respiratory System (21 decks)

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