AAMC 5, Bio section, #122; lung question

[riseNshine]

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Hi everyone,

On the bio section of AAMC #5, for first question in the lung passage (passage 5), I understand the answer, but why does the explanation say venous blood have lower pH...Isn't it that the pulmonary artery has the lower pH due to higher CO2 content and the pulmonary vein leaving the lung ends up with higher O2, lower CO2, and higher pH?

Thanks.

 

[riseNshine]

Also, for #124, why does it say Resistance is inversely proportional to length? Isn't R=pL/A so it should be directly proportional to the length of the tube and since it has to pump across larger distances, it has greater resistance, so it must have higher pressure?

 

[circulus vitios]

Also, for #124, why does it say Resistance is inversely proportional to length? Isn't R=pL/A so it should be directly proportional to the length of the tube and since it has to pump across larger distances, it has greater resistance, so it must have higher pressure?

I haven't taken AAMC 5 and I've never seen the question, but you sure they aren't referring to cross-sectional length or something? Are the tube and pump analogies? Because R=pL/A is for electrical resistance.

 

[MangoPlant]

Venous blood has lower pH because it picks up CO2 from tissues. CO2 combines with H2O in the blood to form H2CO3 which then dissociates to form H+ and HCO3-. The presence of H+ lowers pH. Basically: venous blood has more [CO2] than arterial blood, and more CO2 means lower pH.

 

[circulus vitios]

What MangoPlanet said.

Deoxygenated blood from the heart is pumped through the pulmonary artery to the lungs, where oxygen diffuses into blood and is exchanged for carbon dioxide in the hemoglobin of the erythrocytes. The oxygen-rich blood returns to the heart via the pulmonary veins to be pumped back into systemic circulation."Lung Disease & Respiratory Health Center"

 

[commoncold]

Hi everyone,

On the bio section of AAMC #5, for first question in the lung passage (passage 5), I understand the answer, but why does the explanation say venous blood have lower pH...Isn't it that the pulmonary artery has the lower pH due to higher CO2 content and the pulmonary vein leaving the lung ends up with higher O2, lower CO2, and higher pH?

Thanks.

It is saying that venous blood has a lower pH than the blood in the aorta and that the pH of the venous blood is essentially the same as the pH of the pulmonary artery. Remember than the content of the venous blood and the pulmonary vein are very different. I hope that helps.