oxygen transport Flashcards
What happens after o2 exchange before o2 is transported?
what happens before o2 is dropped off at tissues?
what must o2 do before it is transported?
o2 exchange at the lung o2 dissolved in plasma (PaO2) o2 bound to HB and then, o2 dissolved in plasma o2 diffuses into tissues
Gases carried in the blood first dissolves in the plasma before mostly being transported in other forms
How is o2 mainly transported?
percentages?
O2 transport
HbO2 = 98%
Dissolved O2 = 2%
Why is dissolved o2 not a good transport mechanism?
As oxygen has relatively low solubility in water (0.2 mL/L/kPa), the partial pressure of oxygen present within alveoli (14 kPa) would only result in approximately 3 mL of oxygen dissolving per litre of blood.
As the body consumes approximately 250 mL of oxygen per minute at rest, this would require a cardiac output of approximately 80L to supply sufficient oxygen to tissues – this is also a massive underestimate as it requires PvO2 to be zero.
Why is haemoglobin critical to O2 transport?
The presence of haemoglobin overcomes this problem – it enables O2 to be concentrated within blood (↑ carrying capacity) at gas exchange surfaces and then released at respiring tissues.
The vast majority of O2 transported by the blood is bound to haemoglobin (>98%).
Has a high affinity for o2
o2 partial pressure (PaO2) expressed as kPa
what does this measure and not measure
“the partial pressure of O2 within a gas phase (at a gas-liquid interface) that would yield this much O2 in the plasma at equilibrium
This doesn’t measure how much o2 is bound to haem or total content of o2 in blood
Total O2 content (CaO2), expressed as mL of O2 per L of blood (ml/L)
what does this measure and include in its measurement
the volume of O2 carried in each litre of blood, including O2 dissolved in the plasma and O2 bound to Hb
This includes the o2 bound to haem + o2 dissolved in the plasma
O2 saturation (SaO2 = measured directly in arterial blood, SpO2 = estimated by pulse oximetry), expressed as %
what does the % indicate?
why does it not tell us total amount of o2?
the % of total available haemoglobin binding sites that are occupied by oxygen
on its own, doesn’t tell us the total amount of o2 as depending on how much haemoglobin you have times the %, you may have a different potential amount of o2 to someone with the same or different level of stauration of their haemoglobin concentration is different
oxygen-haemoglobin dissociation curve (a graph showing the effect of PaO2 on Hb-oxygen saturation)
describe the curve?
what gives it this shape?
shows a non-linear (sigmoidal) relationship, where the gradient of the line initially accelerates, before reaching a plateau, which reflects the saturation and decreased availability of free O2 binding sites on the haemoglobin molecule
cooperative binding is what gives it the sigmoidal shape as it is easier to bind o2 once the first o2 is bound
Why is haemoglobin so effective at transporting O2 within the body?
3 reasons? structure and conc of haem? curve?
(1) The structure of Hb produces high O2 affinity, therefore a high level of Hb-O2 binding (and saturation) is achieved at relatively low PO2
2) The concentration of heme groups & Hb contained in RBCs enables high carrying capacity
(3a) The oxygen-haemoglobin binding curve shifts to offload oxygen to demanding tissues
(3b) Hb O2 affinity changes depending on the local environment, enabling O2 delivery to be coupled to demand
The structure of Hb produces high O2 affinity, therefore a high level of Hb-O2 binding (and saturation) is achieved at relatively low PO2
The effect of this relationship and the high overall oxygen affinity of haemoglobin is that a relatively low PO2 is required for high saturation of Hb binding sites.
E.g. PaO2 must fall below 8 kPa for Hb-O2 saturation to fall below 90%, whereas PAO2 is typically around 14 kPa ,
the concentration of heme groups & Hb contained in RBCs enables high carrying capacity
can carry 197ml by HB
4 haem groups
270 mill haemoglobin per rbc
(3a) The oxygen-haemoglobin binding curve shifts to offload oxygen to demanding tissues
leftward shift - effect and where?
rightward shift - effect and where?
Leftward shift = higher Hb-O2 affinity = Hb binds more o2 at a given PO2
This is usually in less hardworking tissues like the lungs where it can load o2
Rightward shift = lower Hb-O2 affinity = Hb binds less O2 at a given PO2
It will give up o2 more readily to hard-working tissues
What factors cause oxygen-haemoglobin binding curve to shift?
4 factors?
what change in these factors will cause the curve to shift to the right? effect of this?
what change in these factors will cause the curve to shift to the left? effect of this?
Increased CO2, increased temperature, decreased pH (acidosis) and increased concentrations of 2,3-diphosphoglycerate (an intermediate of glycolysis, produced within red blood cells during anaerobic metabolism) decrease O2-Hb binding affinity, decreasing oxygen saturation at a given PO2 and effectively releasing O2 from Hb.
Conversely, the opposing effects, namely decreased CO2, decreased temperature, increased pH (alkalosis) and decreased concentrations of 2,3-diphosphoglycerate increase O2-Hb binding affinity, increasing oxygen saturation at a given PO2 and effectively accumulate O2 on Hb.
Bohr effect
what is right shift called? left shift?
what is the bohr effect?
The effect co2 and pH have on Hb-O2 affinity as their binding will change the structure of haemoglobin very slightly which affects o2 affinity
acidosis = right shift alkalosis = left shift
Hb O2 affinity changes depending on the local environment, enabling O2 delivery to be coupled to demand
how does this help with haemoglobins role?
how does it prioritise o2 release?
how does it differ in lungs, resting and working tissue?
These effects further help haemoglobin to carry out its role within the body of storing O2 at respiratory surfaces and releasing them in respiring tissues.
It also helps to prioritise O2 release to the tissues with the greatest demand as the conditions that reflect the greatest need for oxygen, where PO2 & pH is lowest and CO2 is highest, will cause more oxygen to be released
1) Lungs = incresed PO2, decrease PCO2 and increased PH so has high o2 saturation
2) resting tissue = decreased PO2 hence less o2 saturation so o2 moves from Hb to tissue
3) working tissue = a lot less PO2. Also, anaerobic respiration and hypoxia will produce lactic acid (H+), CO2 and 2,3-DPG therefore there is an increased demand for O2 due to increased co2 levels and 2,3-DPG, and decreased ph
hence there is less Hb-O2 affinity + binding therefore a lot less o2 saturation hence a lot more O2 moves from Hb to tissue
