# Blood vesselsWatch

#1
I am facing difficulties in understanding some concepts in cardiovascular system.
The blood pressure is inverse with the size of a vessels, i.e. the lumens, meaning that the smaller the lumen the greater the resistance to flow and so the higher the pressure, however, the blood pressure in the capillaries is very low, but the it has the smallest lumens of blood vessels in the body, so this contradicts the latter principle, because smaller lumens means higher pressure !
And I'd also like to understand the changes in velocity in the blood vessels and why ?
0
2 years ago
#2
I think you have to consider the fact that in each capillary, the volume of blood present is alot lower, decreasing the pressure.In the arteries the volume of blood is alot greater, in addition to the small lumen which increases the pressure.Also dont forget that the blood in the arteries comes directly from the heart, which pumps the blood very forcefully, increasing the pressure. Capillaries get the blood from the arteries, not directly from the heart.

Think of the cardiovascular system as a stream of water or a river . From the water source(ie heart) you get very fast current (arteries)but as you move along the river, the speed of the water starts to decrease until you find that the water has completly slowed down and leads to an ocean (veins). blood in the arteries must move faster than in the veins as the lumen is alot smaller. blood in the veins moves slower as the lumen is alot larger. the change in velocity helps ensures that the volume of blood in both arteies and veins is equal.

sorry for the horrible analogy :P hope that helps

ps : the blood pressure in the capillaries is alot higher than that in the veins
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#3
I really appreciate your instant response!
It really helped, but why is the velocity in veins bigger ?
0
2 years ago
#4
(Original post by Ramzi Zeidan)
I really appreciate your instant response!
It really helped, but why is the velocity in veins bigger ?
velocity in the veins is actually slower xD and i wouldnt really call is velocity.
speed would be a more approprate term. altho the best term to use when talking about veins ,arteries and capillaries is pressure in terms of how they transport blood.

its no problem im happy to help
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