00:01
So now let's take a look
at the capillary.
00:04
Our capillaries are
microscopic vessels
with diameters that are so small
that the red blood cells
have to pass through them
in a single fall line.
00:15
Their walls are just a thin
tunica intima.
00:19
And in the smallest vessels,
only one cell can form
the entire circumference.
00:24
So it's like one cell
just wraps around itself.
00:29
Capillaries also contain parasites
which are spider-shaped stem cells
that help stabilize
the capillary walls,
control permeability,
and also play a role
and vessel repair.
00:43
Capillary supply almost every tissue
except for our cartilage,
our epithelia,
and the cornea
and lens of the eye.
00:52
The function of our capillaries
is to exchange gases,
nutrients,
waste and hormones,
between our blood
and our interstitial fluid.
01:02
All capillary endothelial cells are
joined together by tight junctions,
but there are also gaps
called intercellular clefts.
01:12
These clefts allow passage of fluids
and small solutes
out of the capillary
into the surrounding
interstitium.
01:21
There are three types
of capillaries.
01:24
We have continuous capillaries,
fenestrated capillaries,
and sinusoid capillaries.
01:32
First, the continuous capillaries
are going to be found
most abundantly
in our skin, muscles, lungs
and our central nervous system.
01:42
In the central nervous system,
the continuous capillaries
of the brain are unique.
01:47
This is because they form
our blood brain barrier,
which are totally enclosed
with tight junctions
and contain no intercellular clefts.
01:58
The second type of capillary
are fenestrated capillaries.
02:02
These are found in areas
involved in active filtration
such as in the kidneys.
02:07
Also in areas like the intestines
where absorption is occurring,
and also places where endocrine
hormone secretion is occurring.
02:16
The endothelial cells contain
a Swiss cheese like look to it
with pores called
fenestrations.
02:25
These allow for an increase in the
permeability of these capillaries,
And the fenestrations
are also usually covered
with a very thin
glycoprotein diaphragm.
02:38
The third type of capillary
are a sinusoidal capillaries.
02:43
These have fewer tight junctions,
and are usually fenestrated with
larger intercellular clefts,
an incomplete basement membranes.
02:52
These also usually have
larger lumens
than the other types of capillaries.
02:57
These are found only
in the liver,
bone marrow,
spleen,
and adrenal medulla.
03:04
Blood flow in the sinusoidal
capillaries is sluggish,
which allows time for modification
of large molecules
and blood cells that pass between
the blood and the tissue.
03:17
These also contain macrophages,
which are going to capture and
destroy foreign invaders.
03:25
So if we look at how our capillaries
are arranged in the body,
we find that they are arranged
in capillary beds
or interwoven networks
of capillaries
between our arterioles
and our venules.
03:40
Through these capillary beds,
we have microcirculation,
which is the flow of blood
from the arteriole to the venule
through the capillary bed.
03:52
The capillary bed is going to
consist of two types of vessels.
03:57
First, you have the vascular shunt
which is going to serve
as like a big highway
or thoroughfare channel between
the arteriole and the venule.
04:08
You also have the true capillaries,
which are going to be the
actual vessels
that are going to be involved
in exchange of
nutrients and oxygen.
04:18
So taking a closer look
at the vascular shunt,
we find that the
metarteriole thoroughfare channel
is going to start
at the terminal arteriole
that will then feed into
the metarteriole,
which is going to be intermediate
between the arteriole
and the capillary.
04:36
This is also going to be continuous
with the thoroughfare channel,
which then feeds into the
postcapillary venule
that will then drain the bed
and then send the blood
back toward the heart.
04:51
The other part of the capillary bed
is the true capillaries
were exchanged between
vessels and tissues
is going to take place.
04:59
There are 10 to 100 exchange vessels
per capillary bed.
05:04
These are going to branch off
of the metarteriole
or the terminal arteriole.
05:10
And the true capillaries
are going to normally branch
from the metarteriole and then
return to the thoroughfare channel.
05:19
Also, our true capillaries contain
precapillary sphincters
which are going to be responsible
for regulating blood flow
into the true capillaries.
05:30
These are going to determine
whether blood may go
into the true capillary
or go to the shunt.
05:37
This is going to be regulated
by local chemical conditions
and vasomotor nerves.