BIOL 5240 Exam 6: CO2 Transport Key Concepts

What is the overall mechanism of CO2 transport in the lungs?

At the lungs, everything happens in reverse for CO2 excretion.

What is the rate of CA reaction in the lungs?

CA takes less than a second (0.75 s) for RBC to go through a pulmonary capillary.

What is the mechanism of CO2 uptake and excretion?

CO2 gas secretes H2CO3 which is excreted to CO2 gas.

What is the process of CO2 uptake?

[1] CO2 diffuses into plasma with lots of H2O = CO2 + H2O forms H2CO3 = H+ + HCO3-; this reaction is slow, so most CO2 diffuses into the RBC. [2] CO2 diffuses into RBC with lots of H2O = CO2 + H2O with high concentration of CA = H+ + HCO3- (fast) inside RBCs. [3] Products on the right of RBC will build up so these need to be broken down to keep the reaction going: (a) H+ binds to Hb forming HbH + O2. (b) HCO3- is transported from RBC to plasma by protein in red cell membrane called Band-3 anion exchanger. [4] CO2 can bind to HbO2 to form HbCO2 (10% CO2) + O2.

What are the steps of CO2 excretion?

[1] CO2 gas leaves blood and enters alveoli, lowering CO2. [2] this pulls CA in opposite direction and reverses chloride shift and Bohr shift. [3] excrete CO2 gas from lungs.

What is CO2 generated as?

as a waste product of carbohydrate metabolism.

What does CO2 chemically react with?

can chemically react with H2O to form carbonic acid (H2CO3) to dissociate into H+ and HCO3- (bicarbonate ions); HCO3- can dissociate into H+ and CO3- but is rare.

What is the overall mechanism of CO2 transport in systemic capillaries?

converted CO2 to bicarbonate and shifting it into plasma to be carried to lungs.

Define Chloride Shift:

shifting Cl- into RBC and bicarbonate out.

What is the most produced CO2 species under normal physiological pH?

the most produced chemical species in blood = HCO3-.

What do the forms of CO2 depend on?

these depends on pH.

What type of diffusion occurs by Band-3 anion exchanger?

this is facilitated diffusion exchange for negative charge for negative charge = neutral;

What is the process of band-3 anion exchanger?

this process is called the chloride shift

What is the speed of CO2 + H2O reaction?

this reaction is slow, especially slow toward CO2 + H2O.

Define Band-3 Anion Exchanger:

transmembrane proteins on RBC membrane that grabs bicarbonate and transports it out of RBC in exchange for transporting Cl- into RBC

What buffers H+ ions from making blood more acidic?

when H+ enters the blood, it becomes more acidic, but gets buffered by plasma proteins: H+ is attracted to Pro- to keep pH constant.

What are the four potential forms of CO2?

(1) CO2 (2) H2CO3 (3) HCO3- (4) CO3-

What are the concentrations of CO2 forms under normal physiological pH?

(1) CO2 = 5%. (2) HCO3- = 95%. (3) H2CO3 = 0.1%. (4) CO3 = not present.

What are the steps to CO2 formation?

(1) long chain FA with carboxylic acid group on end becomes decarboxylated, (2) hydrogen on COO- joins carbon to form CO2 gas in mitochondria.

Where does CO2 excretion occur?

in the lungs.

Where is CO2 generated?

in the mitochondria.

Where does CO2 uptake occur?

in the systemic capillary, with (a) metabolizing tissue (FPO) on bottom with lots of mitochondria producing CO2 and (b) outside with blood plasma and RBC circulating through capillary.

How does CA facilitate the CO2 + H2O reaction?

it favors direct formation of H+ + HCO2- from CO2 + H2O.

What is the speed of CO2 + H2O + CA reaction?

it is very fast (one of the fastest enzymes known).

What is the role of carbonic anhydrase (CA)?

it speeds up / facilitates the CO2 + H2O reaction.

What is the pH under normal physiology?

normal physiological pH = 7.4.