Oxygen and CO2 in the blood Flashcards
Explain why myoglobin is efficient for muscle
What can you conclude generally about the advantages and disadvantages of myoglobin?
It has a higher affinity for oxygen and needs to be around very low pO2s to unbind. If there’s abundant oxygen around - myoglobin will bind to O2 faster for storage and keep it. However, in strenuous exercise when there’s lower pO2, myoglobin will release it. Therefore, the more oxygen the tissue needs (aka muscle cells) the more myoglobin can give
Myoglobin is good for binding, but not transporting (as it requires a Kpa too low for capillaries to dissociate)
What is the structure of Haemoglobin?
Tetramer: 2 alpha and 2 Beta, quaternary structure
Each subunit has 1 haem + globin
What states/moods does haemoglobin have?
How does this generate haemoglobin’s dissociation curve?
Tense state: doesn’t bind to oxygen well. So when the pO2 is low, it’s hard to bind the first few. Generally in acidic conditions
Relaxed state: loves binding to oxygen, and binding facilitates further binding. Since saturation changes greatly over a narrow range of pO2, a sigmoidal curve is generated
At what pO2 is haemoglobin…
a) saturated
b) unsaturated
c) half saturated
Why does haemoglobin stay well saturated in the lungs?
a) 8.5 kPa
b) <1kPa
c) 3-4.5 kPa
Stays well saturated in the lungs as it’s pO2 is 13.3 kPa, far above 8.5
What is the typical value of tissue pO2?
How high must pO2 be to drive oxygen out of the cells? What can reduce this value?
normally 5kPa, must be at least 3 kPa but the pO2 can fall the higher the capillary density
Explain the Bohr Shift
How is this advantageous in exercise?
In acidic conditions the dissociation curve shifts right on the pO2 axis - so it takes a larger pO2 to get Hb out of its tense state.
In exercise: when there is a lactic acid buildup, the acidity encourages the Hb to remain in T state; binding to less oxygen and giving up more
What is the ‘oxygen reserve’, how much oxygen from this reserve is given up in tissues typically?
The oxygen reserve is the amount of oxygen being transported through arterial blood, about 27% is typically given up in tissues
When does maximum unloading of oxygen occur?
(Keep the Bohr shift in mind) How much oxygen is given up in these areas?
In environments that are acidic and warm, and where the pO2 is very low, about 70% is given up
What is the relevant equation representing pH in the plasma?
CO2 + H2O H+ + HCO3-
What happens to the pH when pCO2 rises and falls?
What happens to the pH if HCO3- rises?
pCO2 rises: pH falls
pCO2 falls: pH rises
HCO3- rises: pH rises
Why does the pH stay alkaline?
We have 25 mmol/L of HCO3 in the plasma that also comes from sodium hydrogen carbonate (and the kidneys)
Explain the Hamburger Shift
H+ that is formed in an RBC binds to Hb, this shifts the reaction to forming more HCO3-
HCO3- is exported into the plasma in exchange for Cl-: also keeping the pH alkaline
What is the key in keeping plasma pH at 7.4?
The RATIO of HCO3-: pCO2, there should be 20X as much HCO3 to dissolved CO2
What does the body automatically do to buffer excessive H+ from changing the pH too much?
H+ then reacts with HCO3- to form CO2 (just like the equation) and the CO2 is breathed out, stopping the pH from changing too much
Why should the veins be at risk of dissolving and why doesn’t this happen?
What happens when venous blood reaches the lungs?
The pCO2 is much higher in the veins, so technically the pH should be low enough to dissolve your veins ….
Doesn’t happen because since the Hb has lost an oxygen, it binds to the extra H+and promotes more HCO3- formation. HCO3- is exported into the plasma (Hamburger shift). Therefore the ratio between pCO2 and HCO3 is maintained
At the lungs: Hb picks up O2 and gives up H+ (so more H+ is available). The equation then shifts left, and more CO2 is formed which is automatically breathed out
