Gas Exchange in Lungs

[TawMus]

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70% of CO2 being transported by the blood is converted to carbonic acid
23% of CO2 is dissolved in the blood
7% of CO2 is attached to hemoglobin

as the blood passes thru the pulmonary capillaries, CO2 diffuses thru the gradient into the lungs.... so what happens to the 70% of the CO2 that is in the form of carbonic acid? is there an enzyme that is opposite of carbonic anhydrase that causes it to change back to CO2?? or does it leave the body in the form of carbonic acid??

 

[RySerr21]

70% of CO2 being transported by the blood is converted to carbonic acid
23% of CO2 is dissolved in the blood
7% of CO2 is attached to hemoglobin

as the blood passes thru the pulmonary capillaries, CO2 diffuses thru the gradient into the lungs.... so what happens to the 70% of the CO2 that is in the form of carbonic acid? is there an enzyme that is opposite of carbonic anhydrase that causes it to change back to CO2?? or does it leave the body in the form of carbonic acid??

the reverse reaction occurs. i dont think there is an enzyme that catalyzes this reaction. carbonic acid is not a gas...we exhale CO2 gas.

the reverse reaction that occurs is HCO3- + H+ --- H2CO3 --- CO2 + H20

 

[TawMus]

So if its not an enzyme that catalyzes this reaction, could it possibily be the increase in pH as O2 enters the capillaries?? or maybe the decrease in pressure in the plueral cavity??

 

[RySerr21]

So if its not an enzyme that catalyzes this reaction, could it possibily be the increase in pH as O2 enters the capillaries?? or maybe the decrease in pressure in the plueral cavity??

im not sure what the stimulus is. likely not necessary to know for the MCAT though. i think as long as you understand the concept of gas exchange at the lungs and at the cells in the body you will be fine.

what are you referring to when you say pH increases as oxygen enters?

 

[TypeSH07]

So if its not an enzyme that catalyzes this reaction, could it possibily be the increase in pH as O2 enters the capillaries?? or maybe the decrease in pressure in the plueral cavity??

I don't know what catalyzes it, but I think previous poster was right in saying the reverse happens. Carbonic acid goes into the cell and the cell ends up giving C02 to the alveoli in exchange for oxygen. So somewhere in that process the carbonic acid was turned back into CO2.

 

[rocuronium]

The reverse reaction (HCO3- -> CO2) is catalyzed by carbonic anhydrase in the RBC (not in the plasma).

What causes the CO2 to leave the blood is the difference in partial pressures of carbon dioxide. Think of the following equation in terms of La Chatelier's principle:

CO2 + H20 <--> H2CO3 <--> HCO3- + H+

If you take away CO2 from the left side (movement from blood to capillaries), the reverse reaction occurs, and you "create" more CO2 to be diffused.

Additionally, very little of the CO2 in the blood is transported as carbonic acid. Most of it is transported as HCO3-.

Hope that helps. Let me know if you have any other questions!

 

[BloodySurgeon]

What I think your looking for is called the "chloride shift." If you really want to know what it is look it up, but it is low yield.

 

[rocuronium]

Yeah. The chloride shift (or Hamburger effect) is the movement of chloride ions opposite the movement of HCO3- ions in order to maintain charge balance.

It most likely will not appear on the MCAT, but I think it's interesting! 😀

 

[BloodySurgeon]

Hey gleek, did u know they are making a new star trek movie (XI). It is suppose to about the story about the beginning of the enterprise.

 

[rocuronium]

I didn't know that. I'm not a huge Star Trek fan, but I find that picture hilarious.