Q CAN SOMEONE HELP???

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Q CAN SOMEONE HELP???

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drshabs
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08/18/04 - 05:20 PM

IT SAYS MORE DISTAL U GO FROM HEART MORE IS PRESSURE IN ARTERY.I.E PRESSURE MORE IN DORSALIS PEDIS THAN RADIAL A.

RESISTANCE IS HIGHEST IN ARTERIOLES AND PRESSURE IS LOST IN OVERCOMING THE RESISTANCE.THEN PRESSURE SHOULD BE LOW ?? :?:

mjl1717
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08/18/04 - 09:10 PM

If you have the aorta, an artery and an arteriole( lets call each one a, b,c,
respectively-pressure will drop from a to c,but the amount of pressure lost will be proportional to the resistance of each segment.
a has greatest press. and greatest radius and greatest wall tension

c has the greatest velocity(inversely related to cross sectional area)
c also has the greatest resistance and smallest radius

flow is the same in all 3 "tubes" in a series system

Both statements are correct/Hope this helps without aid of a diagram!

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andrewr47
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08/18/04 - 09:18 PM

the heart is a pump, so the arteries near the heart would have the highest pressure, hence we take blood pressures on the arm.

on the second point, resistance and pressure are not directly related. Resistance only depends on the vessel radius in the proportion of 1/r^4. Q=(P1-P2)/R. pressure is low in arterioles not because resistance is high, but because it is further away from the heart. the fact that resistance is high causes BLOOD FLOW to be low.

I think this is how it works. Please correct me if i'm wrong.

mash
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08/18/04 - 09:29 PM

(P1-P2) =Q*R
R is inversely realted to radius^4
arterioles ve smallest radius so, highest resistance
largest drop is across the arteioles(pressure lost is proportional to resistance of the segment)

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mani
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08/18/04 - 11:50 PM

drshabs, there are 2 points regarding yr question.
1. we have to consider the effect of gravity as well when we are comparing pressure in 2 vessels
2. at branch sites in th evascular system there is some increase in the pressure. this was stated in kaplan physio

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drshabs
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08/19/04 - 02:21 PM

thanks u guys!! grin

.now some of it entered high resistace area my brain!!

drshabs
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08/19/04 - 02:34 PM

"mani" wrote:
drshabs, there are 2 points regarding yr question.
1. we have to consider the effect of gravity as well when we are comparing pressure in 2 vessels
2. at branch sites in th evascular system there is some increase in the pressure. this was stated in kaplan physio

ur right found same explanation in BRS review also.thanks

docofthebigapple
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08/25/04 - 01:52 PM

The fall in presure because of going away from the heart is actually less than the gain in pressure because of the weight of the whole column of blood standing on the dorsalis pedis artery.

Its true that resistance incresases with decrease in diameter of the vessel and pressure decreases in proportion to decrease in diameter ( rather corresponds to the 4th power of the diameter ), but gravity plays a major role in dorsalis pedis artery.

Do you know the pressure is actually negetive in the superior saggital sinus of the skull in a standing human?

thus gravity is a major player.

Same is in case of the radial artery, when hanging freely by the side, pressure is more than if the limb is raised straight above the head.

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