00:00
The lymphatic vessels are an extensive network
of vessels and they are in the sense the ultimate
in terms of drainage. A small amount of fluid
leaks out of the capillaries as we will talk
about later and the lymphatic vessels make
sure that this fluid doesn't collect in the
space between the cells known as the interstitial
space but is eventually collected in the lymphatic
vessels and brought all the way back into
the chest and into the venous system where
that fluid then becomes part of the blood
and gets into the circulation again so that
we don’t develop swelling or edema in the
peripheral tissues. We will have much more
to say about the lymphatic system later but
just to say the lymphatic system is not just
a series of small vessels that drains excess
fluid in the tissues but it also is connected
to lymph nodes that are scattered throughout
the body as well as the thymus gland in the
neck and the spleen in the abdomen and each
of these components plays a major role in
the immunological systems, that is the defense
system against bacteria and viruses. And of
course there are the small vessels as we mentioned
before. Functions as I have also mentioned
is to return any excess body fluid that leaks
out into the tissues back to the circulation.
01:27
It transports also interestingly enough, fats
from the intestines to the blood so that these
substances can be brought to the liver for
further digestion and distribution as nourishment
to the cells.
01:40
And finally, as I mentioned before, part of
the defense system, part of the major immunological
defense system that defends our body against
infections of a variety of kinds. Let's look
here at the other component of the cardiovascular
system that is the blood vessels themselves.
01:58
As you see, they start with large arteries
that branch down to smaller and smaller arteries
and eventually to the arterioles which as
I mentioned before is the major source of resistance
in this circuit. Then following the arterioles
are the capillaries, that is where the oxygen
is delivered to cells and nutrients are delivered
to cells and waste products such as carbon
dioxide are removed from the cells. The blood
then passes into the venules, very small veins,
and eventually to larger veins and as we have
said, returns to the heart to start the circuit
all over again with supplying of oxygen in
the lungs and loss of carbon dioxide to the
atmosphere. Here again a little more detail
of the various blood vessels. The arteries
convey blood away from the heart to the body
tissues. They bifurcate, that is they divide,
into smaller and smaller vessels eventually
reaching the arterioles which are the smallest
part of the arterial system and that is
where the resistance in the system lies as
I have said before and then the arterioles
connect to the capillaries which are in intimate
connection with the cells of the body allowing
exchange of oxygen, carbon dioxide, nutrients
and waste products as I mentioned before.
Then the blood goes into small venules and
to progressively larger veins and
eventually returns to the right side
of the heart to go to the lungs. Here we see
in a very nice cartoon the arteriole system
coming out of the left side of the heart, branching down
to the arterioles, then into the capillaries,
returning from the capillaries into venules,
and then into larger veins, and then returning
to the right side of the heart in a continuous
circle.
03:50
Now interestingly enough, both within the
arteries and within the veins, there are
some connections between arteries and
arteries and veins and veins. These are
called anastomoses which means connecting
mouths, and this happens where
anytime there are two or more vessels that
merge to supply the same body region. This
is in a sense, if you will, a reserve system so
that if one of these arteries become blocked,
blood will get into the system through the
anastomosis and through the sister artery
that is still there, and veins actually have
even more anastomoses so that if one of the
veins closes down in fact the blood will move
through the anastomosis into another vein
and still get to return from the body. In
a sense it's a reserve system in case one
of the arteries or veins closes down.