I am not sure that the velocity is faster in
veins. It would actually vary more in veins.
Blood in arteries is pumped by the heart, but
it will slow down because of friction with the
walls of the blood vessels (resistance). It is
moving more slowly by the time it gets to the
If you’re standing, blood would have a hard
time getting from your feet to your heart. If you
stood perfectly still for a long time, you might
faint. But every time the muscles contract, they
squeeze blood back to the heart. One-way valves
keep the blood from being squeezed farther away
from the heart. If you’re running a few miles, you
are probably moving that blood back to the heart
very fast. So the velocity of the blood in
veins will vary due to muscle activity. So
will the blood in arteries, but the difference may
be greater in veins.
Higher velocity could mean higher pressure, but
there are other variables to think about. A big
one is the size of the vessels. Think about it
this way, if you fill a balloon with air, then try
to squash it, the pressure goes up. It’s not due
to the speed of the air, it’s because the same
amount of air is being forced into a smaller
container. Likewise, if you want more pressure
out of a hose, you put your thumb over some of the
opening. This reduces the size of the tube
diameter, so the pressure increases. Veins hold
more blood than arteries, so the container is
bigger. This would result in lower pressure.
Why do you think the walls of the veins and
arteries are so different?
This is a great physiology question.
Thanks for asking,
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