PBL 7 - haemoglobin + O2 transport Flashcards
what is the equation for oxygen delivery to tissues?
oxygen delivery to tissues = oxygen content of arterial blood x cardiac output
how many ml of O2 are there per litre of plasma vs. arterial blood?
plasma = about 3ml — O2 is not very soluble in plasma
arterial blood = 200ml = 9mmol/l
each Hb molecule can bind to how many molecules of O2?
4
roughly what is the arterial partial pressure of O2?
13kPa
what is the saturation fo O2 at 13kPa?
97%
50% saturation is at what partial pressure of O2?
4kPa (vs. 13kPa for 97%)
what is a low partial pressure of O2 associated with?
low pp associated with the majority of the Hb molecules being in the tense state with low affinity (vs. relaxed state at higher pp)
describe the tense vs relaxed configuration for Hb in terms of O2 affinity
tense = low affinity for O2 relaxed = increased affinity for O2
what is the equation for O2 delivery of arterial blood?
O2 delivery of arterial blood = (Hb conc x saturation HB) + dissolved O2
what is the % saturation Hb and dissolved O2 proportional to?
the pp of arterial blood
describe how amount of O2 dissolved in plasma increases as partial pressure increases
linear increase
compare the relationship between the pp and saturation of Hb with O2 in a normal vs. anaemic person
the relationship is the same
compare the relationship between O2 content and % saturation in a normal vs anaemic person
the relationship is not the same: for the same PO2, the O2 content of blood is lower in someone with anaemia
describe the effect of increased temperature on the % saturation curve
- increased temp
- decreased affinity
- shift to RHS
- fir the same PO2, saturation is lower
what does a shift to the RHS mean?
= reduced affinity of O2 for Hb
- therefore less saturation of Hb at any given pp
what does a shift to the LHS mean?
= increased affinity of O2 for Hb
- therefore increased saturation of Hb at any given pp
what do a decreased pH and increased temperature both favour?
the offloading of O2 in tissues
describe the effects of a decreased pH on the % saturation curve
- decreased pH (increased acidity)
- decreased affinity
- shift to RHS
- for the same PO2, saturated is decreased
what is 2,3-diphosphoglycerate?
a metabolite in RBCs — produced by RBCs in glycolysis
describe the effect of an increased 2,3-DPG on the % saturation curve
- increased 2,3-DPG
- decreased affinity
- shift to RHS
is stored blood high or low in 2,3-DPG and what is this effect?
stored blood is low in 2,3 DPG (because of low metabolism) — therefore has a high affinity for O2
what are the changes in globin chains with development?
- 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
how does foetal Hb promote uptake of O2 across the placenta?
foetal Hb has a greater affinity for O2 than maternal — foetal Hb is more saturated at any given PO2 than maternal Hb
compare the affinity for O2 of myoglobin vs Hb, what is the effect of this?
- myoglobin has a greater affinity for O2
- favours the movement of O2 from the blood to muscle oxygen stores
compare the O2 affinity of Hb vs carbon monoxide — what can it lead to?
- 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
where can CO come from?
- environment
- smoke
- faulty domestic boilers
in pulse oximetry, does deoxygenated blood absorb more or less red light?
more — bluish colour
in fully saturated O2Hb, is there a lot or little absorption of red light?
little — therefore blood is red
what does the difference between the amount of red light absorbed by deoxygenated blood vs. fully saturated Hb allow us to determine?
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
describe the finger probe
the oximitre compares the relative strengths of what 2 signals to determine the % saturation of Hb, specifically within the arterial blood?
- pulsatile signal in arterial blood
- pulsatile signal in infrared area
what are some sources for error in pulse oximetry?
- 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
what are Howell-Jolly bodies?
= remnants of RBC nuclei that are normally removed by the spleen
- can be present in abnormal RBCs eg. sickle cell disease
describe how sickle cell disease comes about
- comes about because of a simple mutation in the polypeptide chain of the Hb
- single substitution of glu-glu for val
- genetically inherited mutation
in sickle cell disease, a mutation in the B chain results in what Hb?
HbS — has 2 mutant b chains
describe briefly the pathophysiology of sickle cell disease
what is an advantage to carrying HbS?
gives some resistance to malaria
how can the hemeostasis of iron be easily disputed?
- increased breakdown of RBCs
- reduction in the uptake of iron from diet
what happens to the iron when RBCs are broke down?
- some is returned directly to bone marrow for the production of new RBCs
- some is lost through the bowel and lost in faeces
how is any iron lost replaced?
via the diet
