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PBL SEM 2 > PBL 7 - haemoglobin + O2 transport > Flashcards

PBL 7 - haemoglobin + O2 transport Flashcards

1
Q

what is the equation for oxygen delivery to tissues?

A

oxygen delivery to tissues = oxygen content of arterial blood x cardiac output

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2
Q

how many ml of O2 are there per litre of plasma vs. arterial blood?

A

plasma = about 3ml — O2 is not very soluble in plasma

arterial blood = 200ml = 9mmol/l

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3
Q

each Hb molecule can bind to how many molecules of O2?

A

4

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4
Q

roughly what is the arterial partial pressure of O2?

A

13kPa

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5
Q

what is the saturation fo O2 at 13kPa?

A

97%

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6
Q

50% saturation is at what partial pressure of O2?

A

4kPa (vs. 13kPa for 97%)

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7
Q

what is a low partial pressure of O2 associated with?

A

low pp associated with the majority of the Hb molecules being in the tense state with low affinity (vs. relaxed state at higher pp)

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8
Q

describe the tense vs relaxed configuration for Hb in terms of O2 affinity

A 
tense = low affinity for O2
relaxed = increased affinity for O2
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9
Q

what is the equation for O2 delivery of arterial blood?

A

O2 delivery of arterial blood = (Hb conc x saturation HB) + dissolved O2

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10
Q

what is the % saturation Hb and dissolved O2 proportional to?

A

the pp of arterial blood

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11
Q

describe how amount of O2 dissolved in plasma increases as partial pressure increases

A

linear increase

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12
Q

compare the relationship between the pp and saturation of Hb with O2 in a normal vs. anaemic person

A

the relationship is the same

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13
Q

compare the relationship between O2 content and % saturation in a normal vs anaemic person

A

the relationship is not the same: for the same PO2, the O2 content of blood is lower in someone with anaemia

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14
Q

describe the effect of increased temperature on the % saturation curve

A
  • increased temp
  • decreased affinity
  • shift to RHS
  • fir the same PO2, saturation is lower
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15
Q

what does a shift to the RHS mean?

A

= reduced affinity of O2 for Hb

- therefore less saturation of Hb at any given pp

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16
Q

what does a shift to the LHS mean?

A

= increased affinity of O2 for Hb

- therefore increased saturation of Hb at any given pp

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17
Q

what do a decreased pH and increased temperature both favour?

A

the offloading of O2 in tissues

18
Q

describe the effects of a decreased pH on the % saturation curve

A
  • decreased pH (increased acidity)
  • decreased affinity
  • shift to RHS
  • for the same PO2, saturated is decreased
19
Q

what is 2,3-diphosphoglycerate?

A

a metabolite in RBCs — produced by RBCs in glycolysis

20
Q

describe the effect of an increased 2,3-DPG on the % saturation curve

A
  • increased 2,3-DPG
  • decreased affinity
  • shift to RHS
21
Q

is stored blood high or low in 2,3-DPG and what is this effect?

A

stored blood is low in 2,3 DPG (because of low metabolism) — therefore has a high affinity for O2

22
Q

what are the changes in globin chains with development?

A
  • a chain is present in relatively constant concentrations throughout gestation and life
  • y chain is dominant in foetal Hb up until birth
  • y chain is replaced by B chain
23
Q

how does foetal Hb promote uptake of O2 across the placenta?

A

foetal Hb has a greater affinity for O2 than maternal — foetal Hb is more saturated at any given PO2 than maternal Hb

24
Q

compare the affinity for O2 of myoglobin vs Hb, what is the effect of this?

A
  • myoglobin has a greater affinity for O2

- favours the movement of O2 from the blood to muscle oxygen stores

25
Q

compare the O2 affinity of Hb vs carbon monoxide — what can it lead to?

A
  • CO has a 250x affinity for Hb than O2
  • Hb can become fully saturated with CO
  • displaces O2 therefore Hb unable to carry lots of O2
  • tissue hypoxia
26
Q

where can CO come from?

A
  • environment
  • smoke
  • faulty domestic boilers
27
Q

in pulse oximetry, does deoxygenated blood absorb more or less red light?

A

more — bluish colour

28
Q

in fully saturated O2Hb, is there a lot or little absorption of red light?

A

little — therefore blood is red

29
Q

what does the difference between the amount of red light absorbed by deoxygenated blood vs. fully saturated Hb allow us to determine?

A

the % saturation of Hb by shining red light through the tissue and using as a reference point the infrared that is unaffected by the saturation status

oxygenated absorbs more infrared and less red light
deoxygenated absorbs less infrared and more red light

30
Q

describe the finger probe

A
31
Q

the oximitre compares the relative strengths of what 2 signals to determine the % saturation of Hb, specifically within the arterial blood?

A
  • pulsatile signal in arterial blood

- pulsatile signal in infrared area

32
Q

what are some sources for error in pulse oximetry?

A
  • poor perfusion (small pulse)
  • motion
  • excessive light
  • venous pulsation
  • dyshaemoglobins (changes in Hb)
  • nail varnish and skin pigmentation — block penetration of light
  • carbon monoxide — change absorption characteristics of oxy/deoxyhaemoglobin
33
Q

what are Howell-Jolly bodies?

A

= remnants of RBC nuclei that are normally removed by the spleen
- can be present in abnormal RBCs eg. sickle cell disease

34
Q

describe how sickle cell disease comes about

A
  • comes about because of a simple mutation in the polypeptide chain of the Hb
  • single substitution of glu-glu for val
  • genetically inherited mutation
35
Q

in sickle cell disease, a mutation in the B chain results in what Hb?

A

HbS — has 2 mutant b chains

36
Q

describe briefly the pathophysiology of sickle cell disease

A
37
Q

what is an advantage to carrying HbS?

A

gives some resistance to malaria

38
Q

how can the hemeostasis of iron be easily disputed?

A
  • increased breakdown of RBCs

- reduction in the uptake of iron from diet

39
Q

what happens to the iron when RBCs are broke down?

A
  • some is returned directly to bone marrow for the production of new RBCs
  • some is lost through the bowel and lost in faeces
40
Q

how is any iron lost replaced?

A

via the diet

PBL SEM 2 (44 decks)

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