TPR Practice Test 1 B/B Q20

[663697]

According to the scheme depicted in Figure 1, if the carbon dioxide concentration increases within the cell:


A. more Cl– will be secreted into the interstitium.

B. more HCO3– will be secreted into the interstitium. Correct Answer

C. less Cl– will be excreted into the lumen.

D. less H+ will be excreted into the lumen

I chose D for this, I can see why B would be correct but at the moment that CO2 conc increases, wouldn't there be less HCO3- available for secretion??

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[akimhaneul]

According to the scheme depicted in Figure 1, if the carbon dioxide concentration increases within the cell:


A. more Cl– will be secreted into the interstitium.

B. more HCO3– will be secreted into the interstitium. Correct Answer

C. less Cl– will be excreted into the lumen.

D. less H+ will be excreted into the lumen

I chose D for this, I can see why B would be correct but at the moment that CO2 conc increases, wouldn't there be less HCO3- available for secretion??

If the CO2 increases, then according to that diagram, more H2CO3 will be created, which will lead to more H+ and HCO3- being created. Therefore, there will be more H+ available for secretion. D is incorrect.

B is the correct answer because more HCO3- will be created.

 

[663697]

If the CO2 increases, then according to that diagram, more H2CO3 will be created, which will lead to more H+ and HCO3- being created. Therefore, there will be more H+ available for secretion. D is incorrect.

B is the correct answer because more HCO3- will be created.

So do you just think of what would happen after equilibrium is reached again? I thought of it as at the instant that CO2 increases.

 

[aldol16]

Chemically, we always talk about equilibrium unless we're talking about kinetics. This is because at the moment immediately following some change, the system is always infinitesimally similar to the state immediately previous to the change, with the exception of some added stress. So at the infinitesimal moment after you introduce 100 psi of carbon dioxide, there will be no detectable change in the system except for the added 100 psi. The system will then rapidly equilibrate and it's that equilibrium that is relevant in any biological system.

 

[663697]

Chemically, we always talk about equilibrium unless we're talking about kinetics. This is because at the moment immediately following some change, the system is always infinitesimally similar to the state immediately previous to the change, with the exception of some added stress. So at the infinitesimal moment after you introduce 100 psi of carbon dioxide, there will be no detectable change in the system except for the added 100 psi. The system will then rapidly equilibrate and it's that equilibrium that is relevant in any biological system.

That makes sense. Thanks