Kaplan mcat bio question

[anomedic]

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Any help on the following question would be greatly appreciated. I am leaning toward D because of osmosis but not 100% sure. Thank you!

It has been observed that the volume of a red blood cell in venous circulation is normally 3% greater than that of a red blood cell in arterial circulation. The most likely reason for this volume discrepancy is that:

A)The partial pressure of O2 is greater in venous blood than in arterial blood
B)Venous circulation contains three times as much blood volume as arterial circulation
C)There are more red blood cells in venous blood than in arterial blood
D) There is a higher concentration of Cl- in the red blood cells of venous blood than in those of the arterial blood

 

[anomedic]

Bump

 

[anomedic]

Any help would be greatly appreciated!

 

[gettheleadout]

Moved to Q&A.

 

[anticarbon]

I think you are right.

To confirm, check out the following...

http://en.wikipedia.org/wiki/Chloride_shift

Acidic venous blood results in RBC with higher [bicarbonate] which exchanges it for [Cl-], ultimately resulting in higher Cl- concentration in RBC leading to hypertonic cytoplasm leading to bigger cell size.

But I think process of elimination was the intended purpose for this question, as other answer choices seem to be quite obviously not correct.

 

[sps27]

I think you are right.

To confirm, check out the following...

http://en.wikipedia.org/wiki/Chloride_shift

Acidic venous blood results in RBC with higher [bicarbonate] which exchanges it for [Cl-], ultimately resulting in higher Cl- concentration in RBC leading to hypertonic cytoplasm leading to bigger cell size.

But I think process of elimination was the intended purpose for this question, as other answer choices seem to be quite obviously not correct.

Is this a "typo" in Wikipedia.....or am i mis-reading it.....the ans choice D seems to be exact opposite of what Wikipedia says....

Red blood cells are impermeable to hydrogen ions but are able to exchange bicarbonate ions for chloride ions across Band 3. A rise in intracellular bicarbonate causes chloride intake and bicarbonate export. The term "chloride shift" refers to this exchange. As a result, blood chloride concentration is lower in systemic venous blood than in systemic arterial blood or in pulmonary circulation.

 

[gettheleadout]

Is this a "typo" in Wikipedia.....or am i mis-reading it.....the ans choice D seems to be exact opposite of what Wikipedia says....

Red blood cells are impermeable to hydrogen ions but are able to exchange bicarbonate ions for chloride ions across Band 3. A rise in intracellular bicarbonate causes chloride intake and bicarbonate export. The term "chloride shift" refers to this exchange. As a result, blood chloride concentration is lower in systemic venous blood than in systemic arterial blood or in pulmonary circulation.

D is correct. "Blood chloride concentration" refers to plasma chloride concentration. The Cl- has shifted into the RBC's.

 

[anomedic]

Thank you all for confirming my suspicion! and yes, I agree, this is most easily solved by elimination.