Welcome.
In this lecture we will be learning
about the lymphatic system of the body.
The lymphatic system is going to serve
to return fluids that have leaked from our blood vessels
back to our blood.
The lymphatic system consists of three main parts.
You have a network of lymphatic vessels referred to
as the lymphatics.
The fluid inside those vessels referred to as the lymph.
And finally we have the lymph nodes,
which are going to serve to clean that fluid.
The lymphatic system is going to return interstitial fluid
and leaked plasma proteins back to the blood.
Recall that interstitial fluid is that extracellular fluid
formed when components of our blood plasma
leak out of our blood capillaries.
and then while some of that blood plasma is reabsorbed,
the rest of it is going to drain into the lymphatic vessels.
The lymphatic vessels themselves
are an elaborate network of drainage vessels.
They circulate about three liters of interstitial fluid in a day.
And once the interstitial fluid enters the lymphatics,
we then refer to that fluid as the lymph.
Our lymphatic vessels are going to offer
a one way system,
ensuring that the lymph is going to flow
in only one direction
and that is toward the heart.
The lymph vessels also referred to as lymphatics
include lymphatic capillaries,
as well as larger lymphatic vessels.
These blind ended vessels are going to weave
between the tissue cells and our blood capillaries.
They are absent however,
from our bones, teeth, bone marrow
as well as the central nervous system.
Recall the central nervous system
uses the cerebral spinal fluid for drainage
instead of this lymphatic system.
The lymphatic capillaries are very similar
to our blood capillaries,
however, they are a bit more permeable.
Unlike our blood capillaries, the lymphatic capillaries
can take up larger molecules and particles
that the blood capillaries cannot.
So for example,
our lymphatic vessels are able to bring in
proteins,
cell debris,
pathogens,
and even cancer cells.
And sometimes,
the lymphatic vessels, or these lymphatic capillaries
can act as a route for these pathogens or cancer cells
to travel throughout the body.
So depicted here,
you can see the very intimate association
between our lymph capillaries,
which are in green, and the blood capillaries.
Increased permeability of these lymphatic capillaries
are due to multiple specialized structures
two of those include the fact
that endothelial cells overlap very loosely
to form one way valves.
So just like in the veins, we have valves
we also have valves in these vessels.
The many valves are going to be anchored by
collagen filaments to the matrix.
So it's going to increase the extracellular fluid volume
as these many valves open even more.
The decrease in the extracellular fluid will cause
many valves to then close.
Also, in our GI tract in the digestive system,
we have a specialized lymph called Lacteal.
These lymph capillaries are going to absorb digested fats
and deliver fatty lymph or chyle to the blood.
The lymph capillaries are going to drain into
increasingly large vessels.
These vessels are called collecting lymphatic vessels.
These vessels consist of:
collecting vessels,
trunks,
and ducts.
These vessels also have structures and tunics
that are very similar to that of veins.
Except that these are going to have much thinner walls and more valves.
Also, these are going to anastomose more frequently.
The collecting vessels in our skin are going to travel
to our superficial veins,
while the deeper vessels will usually travel to the arteries.
So these larger vessels, also known as lymphatic trunks,
are formed by the union of the largest collecting vessels,
and they're going to drain large areas of the body.
The lymphatic trunks are named for the part of the body
that they drain.
And they include the paired lumbar
which are going to drain the lymph from our lower limbs,
walls of the viscera of the pelvis,
the kidneys,
the adrenal gland,
and the abdominal wall.
The paired bronchomediastinal
which are going to drain the lymph
from the thoracic wall, the lungs, and the heart.
The paired sabclavian
which are going to drain lymph from the upper limbs.
The paired jugular trunks
which are going to join lymph from the head and the neck.
And finally, the single intestinal trunk
which is going to drain lymph from our stomach,
intestines, pancreas, spleen, and parts of the liver.
The lymph is then going to be delivered from these trunks
into one of the two large lymphatic ducts.
We have the right lymphatic duct,
which is going to drain the right upper arm
and the right side of the head and the thorax.
Then we have the thoracic duct,
which drains the entire rest of the body.
In some individuals,
we also have this enlarged sac in the abdominal area
known as Cysterna chyli.
This is where the thoracic duct is going to actually start.
Each of these ducts
are going to empty the lymph into our venous circulation
at the junction of the internal jugular,
and subclavian veins
on each side of the body.