Gas Transport Flashcards
O2 (alv) =
O2 in (lungs) - O2 used (tissues)
Options for carrying O2
Dissolved O2 and hemoglobin.
Solubility of water in blood
0.3 ml O2/dL blood/100 mmHg
Not nearly enough to fulfill O2 demand.
When referring to PaO2:
Partial pressure of O2 in blood refers to dissolved oxygen.
How can we use dissolved O2 as a measure of oxygen bound to Hb?
They are in equilibrium.
At any Po2 > 60 mm Hg:
The Hb is at least 85% saturated with oxygen.
Meaning, O2 content is at least 17 ml O2/dl blood (20.1 ml O2/dl blood x 85% = 17 ml)
The upper right hand corner of the oxygen dissociation curve:
Is a safety zone. PaO2 can decrease somewhat without having deleterious effect on Hb sats.
CO2 and/or pH affect on Hb-O2 curve
Rightward shift. Known as the Bohr effect.
Useful because in areas of high CO2, we want to give up O2, co less affinity is good.
Temperature affect on Hb-O2 curve
Rightward shift. Also helpful because in warm places (tissues) we want to give up O2.
2,3 BPG affect on Hb-O2 curve
Rightward shift.
How does venous PO2 remain at 40 mm Hg?
Not all O2 was used. Therefore there is some remaining in the venous blood (75% O2 sats in venous blood).
20.1 ml O2/dl blood x 75% = 15.2 ml O2/dl blood
The a-v difference
Difference between arterial O2 content and venous O2 content. Represents how much oxygen was used by the tissue being perfused.
19.8 ml O2/dl blood - 15.2 ml O2/dl blood = 4.6 ml O2/dl blood
How might the a-v difference change based on tissue?
Increase in places of increased metabolic output (skeletal muscle) vs lower metabolic output (adipose tissues).
Ratio of O2 to CO2 if carbs are sole fuel source:
1:1 ratio
1 CO2 produced, 1 O2 used
Ratio of O2 to CO2 if fats are sole fuel source:
7:10 ratio (0.7)
7 CO2 produced, 10 O2 used
Normal ratio of CO2 and O2
200 ml CO2 produced/250 ml O2 consumed = 0.8
This is the respiratory quotient. Obviously, both sources are used.
Also can be V(dot) CO2/ V(dOt) O2
Options for carrying CO2
Dissolved CO2 (better than O2, but still not totally sufficient w/ normal CO)
Carbamino compounds
HCO3
Carbamino compounds
CO2 combines with plasma proteins of Hb (just not on the heme). About 7% carried this way.
Haldane shift
Presence of O2 on heme reducing the affinity of the Hb chain for CO2.
Bicarbonate mechanism in the RBC
CO2 + H2O –> H2CO3 –> H+ + HCO3
HCO3 leaves and Cl- and H2O enters. This drives the further production of HCO3.
Catalyzed by carbonic anhydrase.
This occurs in venous blood, so venous RBCs tend to be bigger and have lower plasma Cl-.
How does CO2 move into the alveoli from the RBC?
Dissolved CO2 will travel down its gradient into alveoli.
CO2 and H+ will leave proteins as dissolved CO2 moves into alveoli.
HCO3 will undergo the reverse reaction to produce free CO2 at the lungs and diffuse into the alveoli.
