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Respiratory > 4. Oxygen In The Blood > Flashcards

4. Oxygen In The Blood Flashcards

1
Q

How many oxygen molecules does haemoglobin bind?

A

4

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2
Q

How many oxygen molecules does myoglobin bind?

A

1

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3
Q

Which is more soluble in water, O2 or CO2?

A

CO2

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4
Q

What is myoglobin?

A

Oxygen binding pigment found in muscles, contains haem.

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5
Q

What is the total content of oxygen in muscles?

A

Oxygen bound to myoglobin + oxygen dissolved.

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6
Q

What shape is the oxygen binding curve for myoglobin?

A

Hyperbolic

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7
Q

Binding of oxygen to myoglobin always saturated above a given pO2, so what does the amount of O2 bound depend on?
How might you represent this on a graph?

A

Amount of pigment.

Express saturation as a percentage (how is usually done), rather than amount of oxygen bound.

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8
Q

What subunits make up haemoglobin?

A

2 alpha, 2 beta

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9
Q

What does each subunit of haemoglobin consist of?

A

One haem and one globin.

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10
Q

In what state does haemoglobin have low affinity for oxygen?

A

T-state (tense).

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11
Q

In what state does haemoglobin have a high affinity for oxygen?

A

R-state (relaxed).

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12
Q

What state is haemoglobin in at low pO2?

A

T-state.

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13
Q

What shape is the oxygen binding curve (dissociation curve) for haemoglobin?

A

Sigmoidal curve

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14
Q

What is the normal oxygen content of arterial blood leaving the lungs?

A

Hb conc = 2.2 mol.l^-1.

So oxygen content = 8.8 molecules.l^-1.

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15
Q

At what pO2 is Hb completely saturated? What is pO2 in the lungs?

A

9-10pKa.

Lungs = 13.3kPa.

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16
Q

Why is the oxygen content of the blood of an anaemic person lower?

A

Lungs functioning ok, so haemoglobin is saturating fully, but there is less haemoglobin due to being anaemic, so oxygen content is lower.

17
Q

What is tissue pO2 normally?

A

5kPa.

18
Q

What allows the pO2 of tissues to fall low, thus allowing more oxygen to dissociate from haemoglobin?

A

Higher capillary density (very metabolically active tissues, eg the heart, have higher capillary density).

19
Q

Why does tissue pO2 still need to be fairly high?

A

To drive diffusion of O2 into cells.

20
Q

What is the Bohr shift?

A

Affect of pH on affinity of haemoglobin.
Acid shifts dissociated curve to the right, as promotes the T-state of Hb.
Alkaline shifts dissociation curve to the left, as promotes the R-state).

21
Q

How is extra O2 given up in the most metabolically active tissues?

A

pH is lower (more acidic), so promotes T-state of haemoglobin, and O2 dissociates more easily.
Increased temperature also promotes the T-state of haemoglobin, and O2 dissociated more easily.

22
Q

What conditions does maximum unloading of oxygen occur in?

How much bound oxygen can be given up in these conditions?

A

Tissues where pO2 can fall to a low level (higher capillary density).
More acid environment.
Higher temperature.
70%.

23
Q

In exercise, metabolism can increase by 10 times, but cardiac output only increases by 5 times. How is the oxygen demands of the tissues met?

A

Improved extraction of O2 by the tissues.

24
Q

What affect does 2,3-bisphosphoglycerate have on the oxygen dissociation curve?

A

Shifts dissociation curve to the right, so promotes the T-state of haemoglobin.

25
Q

When do 2,3-BPG levels increase and why?

A

Anaemia and at high altitude.

Allows more O2 to be given up to tissues due to the shift it causes in the oxygen dissociate curve.

26
Q

What happens to 2,3-BPG levels in stored blood?

A

Drop due to refrigeration, so limits how much O2 can be given up at the tissues. This is not normally a problem clinically.

27
Q

What happens in carbon monoxide poisoning?

A

CO reacts with Hb to form COHb. This increases the affinity of unaffected subunits for O2, and therefore O2 is given up less readily at the tissues.

28
Q

At what COHb saturation is carbon monoxide poisoning fatal?

A

> 50%.

29
Q

What is hypoxemia?

A

Low pO2 in arterial blood.

30
Q

What is hypoxia?

A

Low oxygen levels in the body or tissues.

31
Q

What is cyanosis?

A

Bluish colouration due to unsaturated haemoglobin, which is less red than oxygenated haemoglobin.

32
Q

Where is peripheral cyanosis seen and what is it due to?

A

Hands and feet.

Due to poor circulation.

33
Q

Where is central cyanosis seen and what is it due to?

A

Mouth, tongue, lips and mucous membranes.

Due to poorly saturated blood in the systemic circulation.

34
Q

Why can cyanosis be difficult to detect?

A

Poor lighting.

Skin colouration.

35
Q

What does pulse oximetry measure?

A

Level of Hb saturation in pulsatile arterial blood.

36
Q

What does an arterial blood gas measure?

A

Level of Hb O2 saturation, oxygen content, pH, pO2, pCO2, HCO3-.

Respiratory (6 decks)

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