PBL 7 - haemoglobin + O2 transport

Question 1

what is the equation for oxygen delivery to tissues?

Answer 1

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

Question 2

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

Answer 2

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

arterial blood = 200ml = 9mmol/l

Question 3

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

Answer 3

4

Question 4

roughly what is the arterial partial pressure of O2?

Answer 4

13kPa

Question 5

what is the saturation fo O2 at 13kPa?

Answer 5

97%

Question 6

50% saturation is at what partial pressure of O2?

Answer 6

4kPa (vs. 13kPa for 97%)

Question 7

what is a low partial pressure of O2 associated with?

Answer 7

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

Question 8

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

Answer 8

tense = low affinity for O2
relaxed = increased affinity for O2

Question 9

what is the equation for O2 delivery of arterial blood?

Answer 9

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

Question 10

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

Answer 10

the pp of arterial blood

Question 11

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

Answer 11

linear increase

Question 12

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

Answer 12

the relationship is the same

Question 13

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

Answer 13

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

Question 14

describe the effect of increased temperature on the % saturation curve

Answer 14

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

Question 15

what does a shift to the RHS mean?

Answer 15

= reduced affinity of O2 for Hb

- therefore less saturation of Hb at any given pp

Question 16

what does a shift to the LHS mean?

Answer 16

= increased affinity of O2 for Hb

- therefore increased saturation of Hb at any given pp

Question 17

what do a decreased pH and increased temperature both favour?

Answer 17

the offloading of O2 in tissues

Question 18

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

Answer 18

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

Question 19

what is 2,3-diphosphoglycerate?

Answer 19

a metabolite in RBCs — produced by RBCs in glycolysis

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

what are the changes in globin chains with development?

Answer 22

• 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

Question 23

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

Answer 23

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

Question 24

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

Answer 24

• myoglobin has a greater affinity for O2

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

Question 25

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

Answer 25

- 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

Question 26

where can CO come from?

Answer 26

- environment - smoke - faulty domestic boilers

Question 27

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

Answer 27

more — bluish colour

Question 28

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

Answer 28

little — therefore blood is red

Question 29

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

Answer 29

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

Question 30

describe the finger probe

Answer 30

Question 31

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

Answer 31

- pulsatile signal in arterial blood | - pulsatile signal in infrared area

Question 32

what are some sources for error in pulse oximetry?

Answer 32

- 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

Question 33

what are Howell-Jolly bodies?

Answer 33

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

Question 34

describe how sickle cell disease comes about

Answer 34

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

Question 35

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

Answer 35

HbS — has 2 mutant b chains

Question 36

describe briefly the pathophysiology of sickle cell disease

Answer 36

Question 37

what is an advantage to carrying HbS?

Answer 37

gives some resistance to malaria

Question 38

how can the hemeostasis of iron be easily disputed?

Answer 38

- increased breakdown of RBCs | - reduction in the uptake of iron from diet

Question 39

what happens to the iron when RBCs are broke down?

Answer 39

- some is returned directly to bone marrow for the production of new RBCs - some is lost through the bowel and lost in faeces

Question 40

how is any iron lost replaced?

Answer 40

via the diet