Carriage Of Carbon Dioxide Flashcards
Blood carris “total CO2” mainly as _______
HCO3-
Dissolved carbon dioxide [CO2]dis follows __________ and it is in the millimolar range in both blood plasma and blood cells.
Dissolved carbon dioxide
It makes up only ~5% of the total CO2 of arterial blood.
Dissolved carbon dioxide or
Carbamino compounds
Can form either from CO2 and H2O or from H+ and HCO3-
Carbonic acid
It is not quantitatively important for CO2 carriage.
H2CO3 (Carbonic acid)
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].
True
First, Bicarbonate [H2CO3] can dissociate into _____ and _____.
HCO3- and H+
Second, CO2 can combinde directly with OH- to for, HCO3-, the reaction catalyzed by ___________.
Carbonic anhydrase
In arterial blood, HCO3- is ~24mM, so that HCO3- represents _____% of total CO2.
90%
Thus, like H2CO3, ________ is not quantitatively important for CO2 carriage.
CO2− 3 - Carbonate
By far the most important carbamino compound is ________________, which forms rapidly and reversibly as CO2 reacts with free amino groups on Hb.
Carbamino hemoglobin (Hb-NH-COO-)
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.
Total CO2
Van Slyke
CO2 transport depends critically on _____________, _____________ and ______.
Carbonic anhydrase, Cl-HCO3 exchanger and Hb
The total CO2 concentration of arterial blood is ~____ mM or ~___ mL of CO2 gas/dL.
26 mM or 48 mL
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.
4
About 10% of the incremental CO2 moves as _______________, 69% as ______ and 21% as ___________.
Dissolved CO2
HCO3-
Carbamino compounds
Therefore, ________ and _______ are far more important for carrying incremental CO2 to the lungs.
Dissolved CO2 and Carbamino CO2
Some of the incremental CO2 ____% remains in blood plasma throughout its journey to the lungs but most ___% at least intially enters the RBC.
11%
98%
About ___% of incremental CO2 remains dissolved in blood plasma (assuming a hematocrit of 40%)
6%
True or False:
A significant amount forms carbamino compounds with plasma proteins.
False
INSIGNIFICANT AMOUNT
The amount of HCO3- that follows this path depends critically on _______________ which is very low in plasma (~5 mM/ph unit).
Non-HCO3- buffering power
The remaining ~89% of incremental CO2 enters through two “gas channels” ____________ and the _________.
Aquaporin 1 (AQP1) Rh complex
About ___ % of incremental CO2 remains dissolved inside the RBC.
4
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).
True
True or False:
Hb forms carbamino compounds far more easily than do major plasma proteins.
True
Hb forms carbamino compounds even more easily as it _____ O2 in the systemic capillaries (reverse of the CO2-Bohr effect).
Loses
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
False
HEMOGLOBIN
True or False:
About 60% of the incremental CO2 forms HCO−3.
False
64%
Erythrocytes contain a high level of _________________, greatly accelerating the conversion of CO2 to HCO−3.
carbonic anhydrases
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 __________________.
Cl-HCO3 exchanger AE1
Chloride or Hamburger shift.
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.
Dissolved CO2
6%
Erythrocytes
21%
Finally, ~69% of incremental CO2 moves as ______, ____% forms in plasma and ___% that forms inside the RBC.
HCO3-
5%
64%
Because H2O enters the cell during HCO3- formation, erythrocytes _____ as they pass through systemic capillaries.
Swell
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 __________.
Shrink
The ______ in the lungs causes the blood to dump CO2.
High PO2
The carriage of total CO2 in the blood depends on the three blood-gas parameters, _________, __________, and ______.
PCO2, plasma pH and PO2
Each plot shows how changes in PCO2 affect the total CO2 content of blood.
CO2 dissociation curve
Although pH per se does not appear in this diagram, pH __________ as PCO2 increases along the x-axis.
Decreases
In contrast, the O2 dissociation curve is highly nonlinear in its physiological range.
Near-linear relationship in the physiological range of PCO2 and PO2 values.
At any PCO2, total CO2 content rises as PO2 (or Hb saturation) falls- _____________.
Haldane effect
Thus, as blood enters SYSTEMIC CAPILLARIES and releases O2, the CO2-carrying capacity _________ so that blood picks up extra CO2.
Rises
As blood enters the PULMONARY CAPILLARIES and binds O2, the CO2-carrying capacity ______ so that blood dumps extra CO2.
Falls
The ___________ is the flip side of the coin from the pH-Bohr and CO2-Bohr effects.
Haldane effect
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.
H+ release
Just as carbamino formation lowers the O2 affinity of Hb, O2 binding destabilizes carbamino Hb (Hb-NH-COO−), promoting ______________.
CO2 release
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.
46 mm Hg
40 mm Hg
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 ____________.
∼2.7 mL/dL
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.
50%
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.
∼49 mm Hg
The _________ describes the interaction of PO2 and PCO2 in the blood.
O2-CO2 diagram
PCO2 and pH influence the _______________ and PO2 influences the ______________
O2-Hb dissociation curve
CO2 dissociation curve
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 [________]).
Y-Axis/Ordinate
X-Axis/Abcissa
Equal
To be full
Bohr effect: This as PCO2 increases, the O2 content of blood ________.
Decreases
Haldane effect: Thus, as the PO2 increases, the CO2 content of blood ____________.
Decreases
If it were not for the Bohr effect, all the blue curves would be _____________.
Vertical lines
If it were not for the Haldane effect, all the red curves would be ___________.
Horizontal lines
