Gas Transport

Question 1

Oxygen transport is done in what 2 ways in the blood?

Answer 1

Dissolved

Bound to hemoglobin

Question 2

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?

Answer 2

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

Question 3

Describe the structure of hemoglobin

Answer 3

4 heme sites

Globin has 2 alpha chains, 2 beta chains

[adult form is hemoglobin A, fetal form is hemoglobin F]

Question 4

What makes up the x and y-axes of the oxygen dissociation curve?

Answer 4

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

Question 5

Normal [Hb] = ____ g of Hb/100 mL blood

Answer 5

15

Question 6

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)

Answer 6

20.8 mL O2/100 mL blood

Question 7

Oxygen saturation is the % of available sites on Hb that have O2 bound. How would you calculate oxygen saturation?

Answer 7

(O2 combined with Hb/O2 capacity) x 100

Question 8

How does oxygen interact with Hb at normal blood PO2 levels? What about at tissue PO2 levels?

Answer 8

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

Question 9

Hb concentration matters, because what happens to oxygen carrying capacity as Hb concentration decreases?

Answer 9

It decreases REGARDLESS of O2 saturation

[the reverse is true with increase in Hb concentration - oxygen carrying capacity increases regardless of O2 saturation]

Question 10

A left shift of the Hb-O2 dissociation curve indicates what?

Answer 10

Increased affinity of Hb for O2

Question 11

A ______-shift of the O2-Hb dissociation curve indicates a decreased affinity of Hb for O2

Answer 11

Right

Question 12

Which direction does the O2 dissociation curve shift during exercise? Why?

Answer 12

Right

Muscle is acidic and warm - Bohr effect (increase in H+ = decrease in pH, increase in temp)

CO2 production increases (hypercarbic)

Question 13

Which direction does the O2 dissociation curve shift under the influence of 2,3 DPG? When is this present?

Answer 13

Right

End point in RBC metabolism; more of it present during chronic hypoxia

Question 14

What is the difference between arterial blood O2 content versus venous blood O2 content?

Answer 14

PaO2 = 20 mL O2/100 mL blood

PvO2 = 15 mL O2/100 mL blood

Question 15

What is the respiratory quotient?

Answer 15

Relationship/ratio between amount of O2 consumed and CO2 produced

Question 16

The respiratory quotient is the relationship between the amount of O2 consumed and CO2 produced. What determines the respiratory quotient?

Answer 16

The fuel being used (fat vs. carbs)

Question 17

How do different fuel types (carbs vs. fats) affect the respiratory quotient?

Answer 17

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)

Question 18

In what 3 forms is CO2 transported in the blood?

Answer 18

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)

Question 19

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?

Answer 19

No, we produce 200 mL CO2

[2.7 mL is dissolved, 3 mL carried as carbamino compounds, the rest is bicarbonate!]

Question 20

What are carbamino compounds?

Answer 20

CO2 bound to plasma proteins or Hb (binds to amine group, not heme group

Question 21

The _______ shift refers to reduction in Hb amine group affinity for CO2 when O2 is present

Answer 21

Haldane

Question 22

How does CO2 get converted to bicarbonate (HCO3)?

Answer 22

Converted in RBC by carbonic anhydrase

Question 23

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

Answer 23

Chloride; chloride

Question 24

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?

Answer 24

Dissolved CO2 moves down its concentration gradient into the alveoli

CO2 dissociates from proteins

HCO3 is converted back to CO2

Question 25

Compare and contrast O2 and CO2 transport in terms of volume transported

Answer 25

O2: about 20 mL/100 mL blood

CO2: about 50 mL/100 mL blood

Question 26

Compare and contrast O2 and CO2 transport in terms of the major form transported

Answer 26

O2: bound to heme in Hb

CO2: as bicarbonate

Question 27

Compare and contrast O2 and CO2 transport in terms of volume dissolved

Answer 27

O2: 0.3 mL/100 mL blood

CO2: 3 mL/100 mL blood

Question 28

Compare and contrast O2 and CO2 transport in terms of other forms they may be transported (besides dissolved or bound to Hb)

Answer 28

O2: None

CO2: Carbamino compounds

Question 29

What changes in the following lead to a right-shift of the Hb-O2 dissociation curve?

PCO2
pH
Temperature
2,3 DPG

Answer 29

PCO2 increase

pH decrease

Temperature increase

2,3 DPG increase

Question 30

What changes in the following cause a left-shift of the O2-Hb dissociation curve?

PCO2
pH
Temperature
2,3 DPG

Answer 30

PCO2 decrease

pH increase

Temperature decrease

2,3 DPG decrease

Question 31

Fetal hemoglobin exhibits a _____-shift as compared to adult hemoglobin

Answer 31

Left

Question 32

The effect of PCO2 and pH on the O2-Hb dissociation curve is called the __________ _______

Answer 32

Bohr effect

Question 33

How do tissue PCO2 levels affect pH?

Answer 33

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]

Question 34

What is the mechanism behind fetal hemoglobin’s higher affinity for O2 as compared to adult hemoglobin?

Answer 34

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.

Question 35

What changes occur with the Hb-O2 dissociation curve in the presence of CO?

Answer 35

Carbon monoxide reduces the number of sites available for O2 binding to Hb (decreased height of curve) and causes a left shift