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Respiratory System > Oxygen In Blood > Flashcards

Oxygen In Blood Flashcards

1
Q

What two states can haemoglobin have?
How does the affinity differ?

A
  • T state: tense |no O2 bound | low affinity for O2
  • R state: relaxed | O2 bound | higher affinity for O2
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2
Q

Define cyanosis

A

Bluish colouration due to unsaturated haemoglobin
(Deoxygenated Hb is less red than oxygenated Hb)

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3
Q

What is the pO2 in alevolar air?

A

13.3 kPa

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4
Q

What is the pCO2 in alevolar air?

A

5.3 kPa

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5
Q

What is the pO2 in venous blood?

A

6kPa

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6
Q

What is pO2 in alevolar blood?

A

13.3kPa

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7
Q

What is pCO2 in alevolar blood?

A

5.3kPa

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8
Q

What is pCO2 in venous blood?

A

6kPa

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9
Q

Why is haemoglobin needed to transport oxygen?

A
  • Oxygen’s solubility in water is very low
  • there is not enough dissolved O2 in blood to meet the body’s demand
  • Hb is needed to meet the demand + transport oxygen
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10
Q

Why is arterial blood brighter red than venous blood?

A
  • Hb molecules with more O2 bound are brighter red
  • oxygenated arterial blood is brighter than deoxygenated venous blood
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11
Q

What is formed when O2 binds to Hb?

A

Oxyhaemoglobin

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12
Q

Structure of haemoglobin

A
  • 2 alpha + 2 beta subunits
  • Each subunit has 1 haem group containing an iron ion to which O2 binds to
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13
Q

Describe the shape of the haemoglobin-oxygen dissociation curve

A

Sigmoidal shape
First O2 is hard to bind
Easier to bind subsequent O2
Plateaus after 4 bind

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14
Q

What is the cooperatively concept of haemoglobin?

A
  • once the first O2 has bound, a small change in the structure of Hb is made
  • this change makes it easier for O2 to bind
  • it is hard to bind the first O2 molecule but subsequent binding is progressively easier
  • as O2 dissociates, changes in the shape prompts remaining O2 to be released quickly
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15
Q

How do you calculate the total O2 content of the blood?

A

Amount chemically bound + amount dissolved

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16
Q

How much O2 is bound to Hb in arterial blood leaving the lungs?

A

8.8mmol/L

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17
Q

Normal conc of Hb

A

2.2mmol/L

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18
Q

Define hypoxaemia

A

Low pO2 in arterial blood

19
Q

Define hypoxia

A

Low O2 levels in body/tissues

20
Q

How does severe anaemia change oxygen in the blood?

A

O2 sats normal
pO2 normal
Reduced O2 content (less Hb)

21
Q

How low can tissue pO2 get?

A

Cannot fall below 3kPa

22
Q

What does a shift in the haemoglobin oxygen dissociation curve mean?

A
  • R ightward shift: R educed affinity > O2 unloads
  • leftward shift: increased affinity > O2 held on tighter
23
Q

What causes a rightward shift of the Hb-O2 curve?
How does this affect affinity?

A

Increased H+
Increased 2,3-DPG
Increased temp
reduces affinity

24
Q

What causes a leftward shift in the Hb-O2 curve?
How does this affect affinity?

A

Decreased H+
Decreased 2,3-DPG
Decreased temp
CO
increases affinity

25
Q

Why are metabolically active tissues at a lower pH?

A
  • decreased pH shifts curve to right
  • reduced pH promotes the T state of Hb
  • lower affinity for O2
  • O2 unloads
26
Q

What affect does 2,3 DPG have on affinity of Hb for O2?

A

Decrease affinity
Rightwards shift

27
Q

What is the Bohr effect?

A

The rightwards shift of the Hb-O2 dissociation curve when H+ or CO2 bind to Hb causing the release of O2

28
Q

What is the haldane effect?

A

CO2 binding to Hb is higher with deoxygenated than oxygenated Hb

29
Q

What is the mechanism of the haldane effect?

A

Deoxygenated Hb has higher affinity for CO2
Due to allosteric modulation of CO2 binding sites

30
Q

What affect does carbon monoxide have on arterial pO2?

A

No affect
Dissolved levels of O2 remains the same

31
Q

Clinical presentation of carbon monoxide poisoning

A
  • Headache
  • Nausea + vomiting
  • Slurred speech
  • Confusion
32
Q

Who are at an increased risk of CO poisoning?

A

Children

33
Q

How does carbon monoxide poisoning occur?

A
  • CO binds to Hb
  • Hb has 200x affinity for CO than O2
  • reduced O2 transport
  • increases affinity of unaffected subunits for O2
  • leftward shift in Hb-O2 dissociation curve
  • reduced O2 release to peripheral tissues
34
Q

What is peripheral cyanosis due to?

A

Poor local circulation

35
Q

What is central cyanosis due to?

A

Poorly saturated blood in systemic circulation

36
Q

Ways to measure O2 saturation

A

Pulse oximetry
Arterial blood gas

37
Q

Outline pulse oximetry

A

Non invasive way to measure percentage of Hb saturated with O2

38
Q

How does a pulse oximetry work?

A

Detects difference in absorption of light between oxygenated + deoxygenated Hb

39
Q

Downfalls of pulse oximetry

A
  • Less accurate in darker coloured skin
  • Less accurate if patient has poor circulation to peripheries
  • affect by severe anaemia
  • may not be able to differentiate between Hb-CO or mathaemoglobins
40
Q

Outline an arterial blood gas

A
  • Invasive
  • Sample of blood taken form artery (often radial)
  • analysed by machine to assess pO2, pCO2, bicarbonate + pH
41
Q

What cases have high levels of 2,3-DPG?

A

Anaemia
High altitude

42
Q

Difference between partial pressure of O2, Hb saturation of O2 + content of O2

A
  • partial pressure: pressure exerted by O2(in kPa)
  • Hb saturation: how saturated a Hb molecule is with O2 (as a %)
  • content of O2: conc of O2 (in mmol/L)
43
Q

Where do you take blood from in an arterial blood gas?

A

Radial artery

44
Q

If you cant take blood from the radial artery for a ABG, where else could you take blood from?
Why is this not as good of an option?

A
  • Brachial or femoral artery
  • They are less superficial and have delicate structures in close proximity which you do not want to damage such as nerves.

Respiratory System (20 decks)

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