00:01
So our capillary blood pressure
is going to be
much lower than
arterial blood pressure.
00:07
It's going to range from
35 mm Hg at the beginning
of the capillary bed
to 17 mm Hg at the end
of the capillary bed.
00:18
Below capillary pressure
is desirable,
because if the pressure
was too high,
it would rupture the very fragile
and thin-walled capillaries.
00:29
Most of our capillaries are also
very permeable,
so a high pressure would force
the filtrate in the capillary
to leak out into our
interstitial spaces.
00:40
So now moving on
to our veins.
00:43
The venous blood pressure
is going to change very little
during the cardiac cycle.
00:49
There is a small pressure gradient
of only about 15 mm Hg.
00:54
So, if a vein is cut,
the low pressure of the
venous system
is going to cause the blood
to flow out nice and smoothly.
01:03
This is in contrast
when an artery is cut.
01:06
In this case,
blood is going to spurt out
because the artery system
is a much higher pressure system.
01:14
The low pressure in our veins
is due to the cumulative effects
of peripheral resistance,
The energy of the blood pressure
is lost as heat
during each circuit.
01:25
And the low pressure
of the venous side
requires adaptations
in order to help the venous blood
return to the heart.
01:35
The factors that we use to aid
venous return
include the muscular pump,
where the contraction of our
skeletal muscles
milk the blood
back toward the heart.
01:47
At the same time,
valves present within our veins
are going to prevent
backflow of the blood
so that is constantly moving up
and not going backwards.
01:58
We also have a respiratory pump.
02:01
Where pressure changes
during the breathing,
move our blood toward the heart
by squeezing our abdominal veins
and our thoracic veins
as they expand.
02:12
Finally, we have
sympathetic vinoconstriction,
we're under sympathetic control,
the smooth muscles are going to
constrict and push blood
back toward the heart.
02:25
So depicted is the milking action
of the skeletal muscles
that's going to propel
the venous blood
from the lower extremities
toward the heart.