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Flashcards in Oxygen in Blood Deck (23)
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1
Q

How many molecules of oxygen can Haemoglobin and Myoglobin bind and where is each one found?

A

Haemoglobin- 4 O2 molecules found in blood

Myoglobin- 1 O2​ molecule bound, found in in muscle

2
Q

Explain how amount of O2​ bound relates to pO2 using the myoglobin dissociation curve

A

As pO2 increases, amount of O2 bound increases until the pigment is saturated

Therfore amount of O2 is dependent on amount of pigment

3
Q

Why would you show the myoglobin dissociation curve as a % saturation?

A

% saturation shows binding independent of pigment concentration

4
Q

What subunits make up Haemoglobin?

A

A tetramer of 2 alpha & 2 beta subunits

Each subunit has 1 haem and 1 globin

5
Q

Explain the difference between ‘T’ and ‘R’ states of haemoglobin

A
  • ‘T’= tense. Has a low affinity for O2
    • O2 therefore difficult to bind
  • ‘R’= relaxed. Has a high affinity for O2
    • easier for O2 to bind
6
Q

How does the state of Hb change dependent on pO2?

A
  • low pO2 = Hb is ‘T’
  • High pO2= Hb is ‘R’
7
Q

How does O2 binding affect the state of Hb?

A

When no oxygen bound, Hb is T state

As more oxygen binds, the Hb becomes more ‘R’

8
Q

Describe the shape of the Haemoglobin Dissociation Curve

A

Sigmoidal shape

As pO2 increases, % saturation quickly increases until saturated

9
Q

What is the normal concentration of Hb? How does this relate the O2 content of blood?

A

2.2 mmol.l-1 Hb in blood

Each binds 4 O2

(2.2 x4) = 8.8 mmol.l-1 O2 in blood

10
Q

How is O2 given up at metabolically active tissue?

A

Metabolically active tissue has pO2 ~5 kPa

At 5kPa, Hb saturation is 65% meaning 35% is given up at the tissues

In very metabolically active tissue pO2 drops even more → more O2 is given up

11
Q

How does capillary density relate to pO2

A

pO2 can’t fall to below 3 kPa in most tissues

but in very metabolically active tissues a high capillary density means pO2 can afford to drop lower so more O2 is released

12
Q

How does an acidic environment change the binding of O2 to Hb? In which direction would the curve shift?

A

Bohr-Shift - Curve shifts the the Right

Decrease in pH promotes ‘T’ state of Hb, Increase in pH promotes ‘R’ state of Hb

13
Q

What is the effect of the Bohr Shift in metabolically active tissues?

A

Metabolically active tissues have lower pH

low pH promotes ‘T’ state so more O2 is given up to meet demand

14
Q

How does temperature affect the oxygen dissociation curve?

How does this relate to metabolically active tissues?

A

Increased temperature shifts the curve to the right

Metabolically active tissues have a higher temperature so more O2 given up

15
Q

What is the effect of an increase in 2,3 BPG on the O2 dissociation curve?

In what circumstances would BPG levels rise?

A

Increase 2,3 BPG shifts the curve to the right

BPG rises at altitude or in anaemia

16
Q

How does Carbon monoxide poisoning affect Hb?

A

CO binds irreversibly with Hb to form COHb

Increased affinity of unaffected subunits for O2 ⇒ won’t give up O2 at tissues

Shape of curve no longer sigmoid

17
Q

How does anaemia affect the shape of the O2 binding curve?

A

Curve is still sigmoidal and will give up O2 at tissues but is Hb lower so does not have as much O2 bound

18
Q

What is the difference between Hypoxemia and Hypoxia?

A

Hypoxemia = low pO2 in arterial blood

Hypoxia = low O2 levels in body or tissues

19
Q

What is cyanosis?

A

Bluish colouration due to unsaturated Hb

20
Q

Distinguish between central and peripheral cyanosis

A

Central = around mouth, lips, mucous membranes due to poorly saturated blood in systemic circulation

  • usually a cardiac defect/ lung problem

Peripheral= due to poor local circulation in hands and feet

21
Q

What does pulse oximetry measure and how?

A

Oxygen saturation

Detects pulsatile areterial blood by red and infrared light

22
Q

Why would pulse oximetry show normal % saturation even in an anaemic patient?

A

Doesn’t detect how much Hb is present

The Hb that is present will still be fully saturated so gives a normal reading

23
Q

What does arterial blood gas analysis measure? How is it taken?

A

Total O2 content of blood

Arterial puncture from radial artery