ALIAA
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1.Within zone II "middle zone" in the lung, flow occurs:
a. during diastole only.
b. during systole and diastole.
c. during systole only.
d. periodically during diastole.
2. Pulmonary vascular resistance increases:
a. at high altitude.
b. during zero gravity (e.g space flight).
c. with anemia.
d. on exercise.
e. all of the above.
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| ssrpk
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b. during systole and diastole
a. at high altitude.
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| jamdoc
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ssrpk can u explain why its b for quest.1?
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| ssrpk
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zone II is at the same level as heart, thus there won't be any loss of pressure due to gravity effect, and blood can flow even during diastole due to low resistance of the pulmonary vessels! this stems from the fact that the mid zone and the lower zone are better ventilated than the apices [remember that more compliant alveoli will accomodate a larger increase in volume], therefore there is no hypoxic vasoconstriction which would increase the pulmonary vascular resistance as it does in the apices, this is why blood flow through the apices occur only during systole!
however during excercise rate of ventilation increases, and so does the blood flow in all three zones and thus the optimal Va/Q of 0.8 is spread in all three zones of the lung!
i hope it helps!
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| jamdoc
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thanks for explanation.
u mean to say that if an organ is at the level of heart,then blood flow occurs even during diastole?
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| fox
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ssrpk wrote:
zone II is at the same level as heart, thus there won't be any loss of pressure due to gravity effect, and blood can flow even during diastole due to low resistance of the pulmonary vessels! this stems from the fact that the mid zone and the lower zone are better ventilated than the apices [remember that more compliant alveoli will accomodate a larger increase in volume], therefore there is no hypoxic vasoconstriction which would increase the pulmonary vascular resistance as it does in the apices, this is why blood flow through the apices occur only during systole!
however during excercise rate of ventilation increases, and so does the blood flow in all three zones and thus the optimal Va/Q of 0.8 is spread in all three zones of the lung!
i hope it helps!
mid zone & lower zone are not ventilated better than apices!!!! Its the opposite!
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| ssrpk
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in terms of absolute values, the rate of ventilation in lower and mid zones are indeed higher than in the apices, however if circulation is taken into consideration, then apex are overventilated while bases are underventilated!
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| ssrpk
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jamdoc, the flow during systole and diastole is controlled by various factors, most important is the resistance, which in tunr is further controlled by various factors like tissue metabolism!
in pulmonary circuit, flow is determined by two factors, venous return and cardiac output! if they are higher they will negate all the effects of higher pulmonary resistance in the apices as in excercise and flow would occur even in diastole!
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| jamdoc
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thank u very much for the explanation
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| ManuNastai
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fox, he's right!
V and Q are higher in the lower lobe. it's V/Q that is higher in the upper lobe than in the lower lobe
PS: I usually hate it when i see his posts after mine, 'cause it usually means I'm wrong.. and it deepens my depression.. I learn a section, comes a Question, I think I got it right and here comes ssrpk and shows me I didn't!!  Keep on going man, you're an inspiration for all of us
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| ssrpk
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hahaha.....cmon man! lolz! i never meant to depress u, ur progress are admirable, tht TTP and HUS thing...tht was a great summary!
besides i believe the most important thing is to search out for the correct info...been doing tht for the last couple of yrs [proud of tht coz i learned a lot here]
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| Addicudo
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Refering to Question 2. Pulmonary Vascular Resistance should Increase whenever there is Vasoconstriction .. and Since pulmonary vascular bed is the only which Vasoconstricts in the presence of Hypoxia .. .. then Y aint all the other options been taken into consideration .. and .. therefore .. E) All of the above .. ???
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| ssrpk
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hypoxic vasoconstriction occurs in response to alveolar PO2, not arterial PO2! besides pulmonary vessela are very compliant which means whenever plumonary blood flow increases vessels dilate so tht pressure does'nt shoot up!
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| Addicudo
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huMm .. OK .. !! Got the point .. !! MisSed the Alveolar 02 point .. thought it was Arterial P02 !! 
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| Addicudo
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But wont the Alveolar ultimately lead to Low Arteriolar p02 .. and there by Vasoconstriction .. ?
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| ssrpk
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true indeed, now tell me which of the other conditons in the list wud lead to LOW ATERIAL PO2 ...... [none of them] 
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