Carriage Of Carbon Dioxide

Question 1

Blood carris “total CO2” mainly as _______

Answer 1

HCO3-

Question 2

Dissolved carbon dioxide [CO2]dis follows __________ and it is in the millimolar range in both blood plasma and blood cells.

Answer 2

Dissolved carbon dioxide

Question 3

It makes up only ~5% of the total CO2 of arterial blood.

Answer 3

Dissolved carbon dioxide or

Carbamino compounds

Question 4

Can form either from CO2 and H2O or from H+ and HCO3-

Answer 4

Carbonic acid

Question 5

It is not quantitatively important for CO2 carriage.

Answer 5

H2CO3 (Carbonic acid)

Question 6

True or False:

Because the equilibrium constant governing the reaction CO2 + H2O H2CO3 is ∼0.0025, [H2CO3] is only 1/400th as large as [CO2].

Answer 6

True

Question 7

First, Bicarbonate [H2CO3] can dissociate into _____ and _____.

Answer 7

HCO3- and H+

Question 8

Second, CO2 can combinde directly with OH- to for, HCO3-, the reaction catalyzed by ___________.

Answer 8

Carbonic anhydrase

Question 9

In arterial blood, HCO3- is ~24mM, so that HCO3- represents _____% of total CO2.

Answer 9

90%

Question 10

Thus, like H2CO3, ________ is not quantitatively important for CO2 carriage.

Answer 10

CO2− 3 - Carbonate

Question 11

By far the most important carbamino compound is ________________, which forms rapidly and reversibly as CO2 reacts with free amino groups on Hb.

Answer 11

Carbamino hemoglobin (Hb-NH-COO-)

Question 12

The reason we group together the previously listed five CO2-related compounds under the term ________ is that the method ______ introduced in the 1920 which remains the basis for assaying blood HCO3- in modern clinical laboratories cannot distinguish among the five.

Answer 12

Total CO2

Van Slyke

Question 13

CO2 transport depends critically on _____________, _____________ and ______.

Answer 13

Carbonic anhydrase, Cl-HCO3 exchanger and Hb

Question 14

The total CO2 concentration of arterial blood is ~____ mM or ~___ mL of CO2 gas/dL.

Answer 14

26 mM or 48 mL

Question 15

As blood courses through the systemic capillary beds, it picks up _____ mL/dL of CO2 so that the total CO2 of mixed-venous blood is ~52 mL/dL.

Answer 15

4

Question 16

About 10% of the incremental CO2 moves as _______________, 69% as ______ and 21% as ___________.

Answer 16

Dissolved CO2
HCO3-
Carbamino compounds

Question 17

Therefore, ________ and _______ are far more important for carrying incremental CO2 to the lungs.

Answer 17

Dissolved CO2 and Carbamino CO2

Question 18

Some of the incremental CO2 ____% remains in blood plasma throughout its journey to the lungs but most ___% at least intially enters the RBC.

Answer 18

11%

98%

Question 19

About ___% of incremental CO2 remains dissolved in blood plasma (assuming a hematocrit of 40%)

Answer 19

6%

Question 20

True or False:

A significant amount forms carbamino compounds with plasma proteins.

Answer 20

False

INSIGNIFICANT AMOUNT

Question 21

The amount of HCO3- that follows this path depends critically on _______________ which is very low in plasma (~5 mM/ph unit).

Answer 21

Non-HCO3- buffering power

Question 22

The remaining ~89% of incremental CO2 enters through two “gas channels” ____________ and the _________.

Answer 22

Aquaporin 1 (AQP1)
Rh complex

Question 23

About ___ % of incremental CO2 remains dissolved inside the RBC.

Answer 23

4

Question 24

True or False:

First, the Hb concentration inside RBCs (∼33 g/dL) is far higher than that of albumin and globulins in plasma (∼7 g/dL).

Answer 24

True

Question 25

True or False:

Hb forms carbamino compounds far more easily than do major plasma proteins.

Answer 25

True

Question 26

Hb forms carbamino compounds even more easily as it _____ O2 in the systemic capillaries (reverse of the CO2-Bohr effect).

Answer 26

Loses

Question 27

True or False:

CO2 is a far better buffer than the plasma proteins for the H+ formed as a byproduct in carbamino formation and becomes an even better buffer as it loses O2 in the systemic capillaries

Answer 27

False

HEMOGLOBIN

Question 28

True or False:

About 60% of the incremental CO2 forms HCO−3.

Answer 28

False

64%

Question 29

Erythrocytes contain a high level of _________________, greatly accelerating the conversion of CO2 to HCO−3.

Answer 29

carbonic anhydrases

Question 30

The _______________ transports some of the newly formed HCO3- out of the cell, promoting formation of more HCO−3. This uptake of Cl− in exchange for HCO−3 is known as the __________________.

Answer 30

Cl-HCO3 exchanger AE1

Chloride or Hamburger shift.

Question 31

The combined effects of the described intracellular and extracellular events is that ∼10% of incremental CO2 formed in systemic tissues moves to the lungs as ___________, ___% in plasma and 4% inside ___________. About ___% moves as carbamino compounds, almost exclusively inside erythrocytes as carbamino Hb.

Answer 31

Dissolved CO2
6%
Erythrocytes
21%

Question 32

Finally, ~69% of incremental CO2 moves as ______, ____% forms in plasma and ___% that forms inside the RBC.

Answer 32

HCO3-
5%
64%

Question 33

Because H2O enters the cell during HCO3- formation, erythrocytes _____ as they pass through systemic capillaries.

Answer 33

Swell

Question 34

When mixed-venous blood (with a PCO2 of ∼46 mm Hg) reaches the pulmonary capillaries (surrounded by alveoli with a PCO2 of only ∼40 mm Hg), CO2 moves from the erythrocytes and blood plasma into the alveolar air space. All of the reactions discussed earlier reverse. In the process, Cl− and H2O leave the erythrocytes, and the cells __________.

Answer 34

Shrink

Question 35

The ______ in the lungs causes the blood to dump CO2.

Answer 35

High PO2

Question 36

The carriage of total CO2 in the blood depends on the three blood-gas parameters, _________, __________, and ______.

Answer 36

PCO2, plasma pH and PO2

Question 37

Each plot shows how changes in PCO2 affect the total CO2 content of blood.

Answer 37

CO2 dissociation curve

Question 38

Although pH per se does not appear in this diagram, pH __________ as PCO2 increases along the x-axis.

Answer 38

Decreases

Question 39

In contrast, the O2 dissociation curve is highly nonlinear in its physiological range.

Answer 39

Near-linear relationship in the physiological range of PCO2 and PO2 values.

Question 40

At any PCO2, total CO2 content rises as PO2 (or Hb saturation) falls- _____________.

Answer 40

Haldane effect

Question 41

Thus, as blood enters SYSTEMIC CAPILLARIES and releases O2, the CO2-carrying capacity _________ so that blood picks up extra CO2.

Answer 41

Rises

Question 42

As blood enters the PULMONARY CAPILLARIES and binds O2, the CO2-carrying capacity ______ so that blood dumps extra CO2.

Answer 42

Falls

Question 43

The ___________ is the flip side of the coin from the pH-Bohr and CO2-Bohr effects.

Answer 43

Haldane effect

Question 44

First, just as H+ binding lowers the O2 affinity of Hb, O2 binding destabilizes protonated hemoglobin (Hb-H+), promoting ____________. By mass action, this H+ reduces CO2-carrying capacity by favoring the formation of CO2 from both carbamino Hb and HCO−3.

Answer 44

H+ release

Question 45

Just as carbamino formation lowers the O2 affinity of Hb, O2 binding destabilizes carbamino Hb (Hb-NH-COO−), promoting ______________.

Answer 45

CO2 release

Question 46

Because CO2 dissociation curves are much steeper than O2 dissociation curves, PCO2 must increase from 40 mm Hg in arterial blood to only _____________ in mixed-venous blood to increase the CO2 content by the ∼4 mL/dL of CO2 required to remove CO2 as fast as the mitochondria produce it. In contrast, PO2 must decrease from 100 to ___________ to dump enough O2 to meet metabolic demands.

Answer 46

46 mm Hg

40 mm Hg

Question 47

If it were not for the Haldane effect, the blood would remain on the red curve, and the PCO2 increase would cause the CO2 content to increase by only ____________.

Answer 47

∼2.7 mL/dL

Question 48

Thus, at a PCO2 of 46 mmHg, the fall in PO2 that occurs as blood flows through systemic capillaries allows the blood to pick up ____% more CO2.

Answer 48

50%

Question 49

Viewed differently, if it were not for the Haldane effect, mixed-venous PCO2 would have to increase to _________ for blood to carry 4 mL/dL of CO2.

Answer 49

∼49 mm Hg

Question 50

The _________ describes the interaction of PO2 and PCO2 in the blood.

Answer 50

O2-CO2 diagram

Question 51

PCO2 and pH influence the _______________ and PO2 influences the ______________

Answer 51

O2-Hb dissociation curve

CO2 dissociation curve

Question 52

On a coordinate system with PCO2 on the _______ and PO2 on the _________, each blue curve in Figure 29-11 represents an ISOPLETH OF IDENTICAL O2 CONTENT in whole blood (from the Greek isos [_______] + plethein [________]).

Answer 52

Y-Axis/Ordinate
X-Axis/Abcissa

Equal
To be full

Question 53

Bohr effect: This as PCO2 increases, the O2 content of blood ________.

Answer 53

Decreases

Question 54

Haldane effect: Thus, as the PO2 increases, the CO2 content of blood ____________.

Answer 54

Decreases

Question 55

If it were not for the Bohr effect, all the blue curves would be _____________.

Answer 55

Vertical lines

Question 56

If it were not for the Haldane effect, all the red curves would be ___________.

Answer 56

Horizontal lines