Gas Transport Flashcards
Oxygen transport is done in what 2 ways in the blood?
Dissolved
Bound to hemoglobin
Oxygen transport is done in 2 ways in the blood: dissolved and bound to hemoglobin. Why isn’t oxygen transport via dissolving in the blood adequate?
Solubility of O2 is limited at 0.003 mL O2/100 mL blood/mm Hg, so there is only about 3 mL dissolved O2/L blood.
During exercise, tissue demands may be 3000 mL O2/min, greatly exceeding the amount of oxygen that can be dissolved in the blood and requiring the use of hemoglobin for more efficient transport
Describe the structure of hemoglobin
4 heme sites
Globin has 2 alpha chains, 2 beta chains
[adult form is hemoglobin A, fetal form is hemoglobin F]
What makes up the x and y-axes of the oxygen dissociation curve?
X axis = PO2 in mm Hg
Left Y axis = % O2 saturation (aka the % of sites on Hb that have oxygen bound)
Right Y axis = O2 concentration in mL/100 mL
Normal [Hb] = ____ g of Hb/100 mL blood
15
Normal [Hb] = 15 g Hb/100 mL blood
1 g Hb can combine with 1.39 mL O2
What is the normal oxygen concentration of the blood (in mL O2/100 mL blood)
20.8 mL O2/100 mL blood
Oxygen saturation is the % of available sites on Hb that have O2 bound. How would you calculate oxygen saturation?
(O2 combined with Hb/O2 capacity) x 100
How does oxygen interact with Hb at normal blood PO2 levels? What about at tissue PO2 levels?
At blood PO2 levels, oxygen readily binds to Hb, and Hb readily hangs onto oxygen
At tissue PO2 levels, oxygen readily jumps off Hb and Hb readily releases oxygen
Hb concentration matters, because what happens to oxygen carrying capacity as Hb concentration decreases?
It decreases REGARDLESS of O2 saturation
[the reverse is true with increase in Hb concentration - oxygen carrying capacity increases regardless of O2 saturation]
A left shift of the Hb-O2 dissociation curve indicates what?
Increased affinity of Hb for O2
A ______-shift of the O2-Hb dissociation curve indicates a decreased affinity of Hb for O2
Right
Which direction does the O2 dissociation curve shift during exercise? Why?
Right
Muscle is acidic and warm - Bohr effect (increase in H+ = decrease in pH, increase in temp)
CO2 production increases (hypercarbic)
Which direction does the O2 dissociation curve shift under the influence of 2,3 DPG? When is this present?
Right
End point in RBC metabolism; more of it present during chronic hypoxia
What is the difference between arterial blood O2 content versus venous blood O2 content?
PaO2 = 20 mL O2/100 mL blood
PvO2 = 15 mL O2/100 mL blood
What is the respiratory quotient?
Relationship/ratio between amount of O2 consumed and CO2 produced
The respiratory quotient is the relationship between the amount of O2 consumed and CO2 produced. What determines the respiratory quotient?
The fuel being used (fat vs. carbs)
How do different fuel types (carbs vs. fats) affect the respiratory quotient?
Carbs - 1:1 ratio (1 CO2 produced for every 1 O2 consumed)
Fat - 7:10 ratio (7 CO2 produced for every 10 O2 consumed)
Usually a mixed bag of fuels with RQ = 0.8 (200 mL CO2 produced for every 250 mL O2 consumed)
In what 3 forms is CO2 transported in the blood?
Dissolved CO2 (5% in arterial blood, 10% in venous blood)
Carbamino compounds (5% in arterial blood, 30% in venous blood)
As HCO3 (90% in arterial blood, 60% in venous blood)
The solubility of CO2 is 6 mL CO2/dL blood/100 mm Hg
PvCO2 = 45 mm Hg
= 2.7 mL dissolved CO2/100 mL blood
Is this enough to rely on dissolved transport alone?
No, we produce 200 mL CO2
[2.7 mL is dissolved, 3 mL carried as carbamino compounds, the rest is bicarbonate!]
What are carbamino compounds?
CO2 bound to plasma proteins or Hb (binds to amine group, not heme group
The _______ shift refers to reduction in Hb amine group affinity for CO2 when O2 is present
Haldane
How does CO2 get converted to bicarbonate (HCO3)?
Converted in RBC by carbonic anhydrase
CO2 is converted to HCO3 by carbonic anhydrase in the RBC.
HCO3 is then exported from the cell by _______, referred to as the ____-shift or hamburger shift
Chloride; chloride
CO2 is transported in the blood in the dissolved form, as carbamino compounds, and as bicarbonate. What happens with each of these forms when they return to the lungs?
Dissolved CO2 moves down its concentration gradient into the alveoli
CO2 dissociates from proteins
HCO3 is converted back to CO2
Compare and contrast O2 and CO2 transport in terms of volume transported
O2: about 20 mL/100 mL blood
CO2: about 50 mL/100 mL blood
Compare and contrast O2 and CO2 transport in terms of the major form transported
O2: bound to heme in Hb
CO2: as bicarbonate
Compare and contrast O2 and CO2 transport in terms of volume dissolved
O2: 0.3 mL/100 mL blood
CO2: 3 mL/100 mL blood
Compare and contrast O2 and CO2 transport in terms of other forms they may be transported (besides dissolved or bound to Hb)
O2: None
CO2: Carbamino compounds
What changes in the following lead to a right-shift of the Hb-O2 dissociation curve?
PCO2
pH
Temperature
2,3 DPG
PCO2 increase
pH decrease
Temperature increase
2,3 DPG increase
What changes in the following cause a left-shift of the O2-Hb dissociation curve?
PCO2
pH
Temperature
2,3 DPG
PCO2 decrease
pH increase
Temperature decrease
2,3 DPG decrease
Fetal hemoglobin exhibits a _____-shift as compared to adult hemoglobin
Left
The effect of PCO2 and pH on the O2-Hb dissociation curve is called the __________ _______
Bohr effect
How do tissue PCO2 levels affect pH?
When metabolic activity of tissues increases, production of CO2 increases
The increase in tissue PCO2 leads to an increase in H+ concentration and a decrease in pH
[together these effects decrease the affinity of Hb for O2, and the curve shifts to the right]
What is the mechanism behind fetal hemoglobin’s higher affinity for O2 as compared to adult hemoglobin?
Fetal hemoglobin has gamma chains instead of beta chains
2,3 DPG (byproduct of RBC glycolysis which reduces affinity for O2) does not bind as avidly to the gamma chains of HbF as it does to the beta chains of HbA. When less 2,3 DPG is bound, the affinity for O2 increases.
What changes occur with the Hb-O2 dissociation curve in the presence of CO?
Carbon monoxide reduces the number of sites available for O2 binding to Hb (decreased height of curve) and causes a left shift
