Why more oxygen goes to alveoli at apex than at base

[Fawad]

Why more oxygen goes to alveoli at apex than at base:

1.inc compliance
2.inc blood flow
3.inc v/q
4.inc pul presure
5.increase alveolar size

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[SBR249]

It doesn't. Ventilation is highest at the base of the lung due to the higher alveolar compliance there.

Source: http://en.wikipedia.org/wiki/Ventilation/perfusion_ratio#Ventilation

 

[lovemango]

It doesn't. Ventilation is highest at the base of the lung due to the higher alveolar compliance there.

Source: http://en.wikipedia.org/wiki/Ventilation/perfusion_ratio#Ventilation

But the V/Q ratio is higher at the apex (ventilation is lower at the apex and higher at the base but the regional difference isn't as huge for ventilation like it is for perfusion), so gas exchange is more efficient at the apex and results in the highest PO2 in the lung (and lower PCO2) when compared to the base. See BRS Physiology, 5e, p. 131.

 

[SBR249]

But the V/Q ratio is higher at the apex (ventilation is lower at the apex and higher at the base but the regional difference isn't as huge for ventilation like it is for perfusion), so gas exchange is more efficient at the apex and results in the highest PO2 in the lung (and lower PCO2) when compared to the base. See BRS Physiology, 5e, p. 131.

Yes, but the OP is asking about oxygen to the alveoli whereas BRS is talking about pulmonary capillary PaO2 and PaCO2. Based on the choices he gave, this question had nothing to do with gas exchange efficiency.

 

[J ROD]

I think that sounds like another crappy Kaplan question.

 

[EazyE1907]

Ventilation and perfusion are BOTH greater at the base of the lung in standing position (due to effects of gravity). TB flourishes in the apex of the lung not because the apex has higher ventilation but because of the ventilation/perfusion ratio is higher at the apex. This means that there is a higher pO2 at the apex of the lungs then there is at the base.

your ans is #3

 

[J ROD]

Ventilation and perfusion are BOTH greater at the base of the lung in standing position (due to effects of gravity). TB flourishes in the apex of the lung not because the apex has higher ventilation but because of the ventilation/perfusion ratio is higher at the apex. This means that there is a higher pO2 at the apex of the lungs then there is at the base.

your ans is #3

That reads and sounds very smart. I will go with that too! 😀

 

[nidusiamnot]

Lol BRS Physio says it best, both V and Q are highest at the base. It's just that the apex doesn't receive as much Q.

 

[Robotman]

Dr. Sattar explains this perfectly.

If you light a match and the blow it out. What direction does the smoke go?

 

[Mad Jack]

It's got to be 3, but this is technically incorrect. The same amount of oxygen GOES TO the base and apex, but the concentration of oxygen after respiration is lower in the apex due to there being less perfusion to scavenge the oxygen present (higher V/Q ratio). This question, it's completely BS.

The pulmonary pressure is the same throughout the lung. Alveoli are not larger in the apex versus the base. The apex of the lung has substantially reduced blood flow when compared to the base due to the effects of gravity. The apex has a higher V/Q ratio than the base. Alveoli are the same size in the apex versus the base, though the base is more compliant leading to the alveoli appearing to be larger.

Now, the air going into your alveoli is 20.9% O2 no matter what part of the lung you're looking at- that's determined by the atmospheric oxygen concentration, period, hence why this question is bull****. But when you exhale, there is a bit of residual air left in your alveoli that mixes with the new oxygen you're taking in. Because there is less perfusion at the apex of the lungs, there is less oxygen being exchanged, meaning that once the air entering your lungs admixes with the gas remaining in your alveoli, it will have a higher O2 concentration than the gas in the alveoli at the base of your lungs. The question should have been phrased as, 'At the end of inspiration, why is the concentration of oxygen higher in the apex as compared to the base of the lungs?"

Kaplan questions are crap.