hi let's have a talk about the lymphatics
the lymphatic system is a part of your cardiovascular system which mirrors the
arteries and the veins it's a means of bringing materials back into the cardiovascular system
that may be lost to the interstitial tissue if you look at this gentleman here you can see that he
is a network of green organs and vessels that all lead back to the thorax here what you can
also determine by the shading is that there is an interesting pattern of drainage and that is that
the right thorax and the right half of the head and neck as well as the right upper limb are all
one drainage unit and the remainder of the body is another drainage unit and so what we have is
this green draining into the right lymphatic duct which enters into the right venous angle and most
of the lymph flow from the body returning back on the left side into the thoracic duct the lymphatic
system is going to mirror the vasculature of the cardiovascular system so it's going to pull back
any plasma from the interstitial tissue back into the cardiovascular system at two locations one
location is the thoracic duct at the left venous angle and the thorax and the other is the right
lymphatic duct at the right venous angle of the thorax seeing from this individual here we can
determine that there are two areas of drainage one that's draining the right upper limb right
half of the thorax and right head and neck and the other that's draining the remainder of the
individual and so that right upper limb right half of the thorax and right half of the head and neck
are going to the right lymphatic duct whereas all of the remainder of the limp is flowing back into
the thoracic duct in addition to reclaiming filtered plasma the lymphatic system is also
an important way of moving fatty acids from the GI system up through the liver and it's a place
for your immune system to be hosted to develop and to mature what we see is that lymphatic
capillaries are embedded and a mesh around the capillaries of the cardiovascular system within
the interstitial tissue lymphatic capillaries are very simple they are one layered cells which you
can see here and there's unidirectional flow of plasma into these lymphatic capillaries
such that they absorb all of that unclaimed filtered plasma from the interstitial tissue now
these lymphatic capillaries feed into lymphatic vessels lymphatic vessels are going to coalesce
into various lymphatic trunks that are generally named for their anatomic position so for instance
on the right side of the slide here we can see both the right lymphatic duct draining into the
right venous angle and the thoracic duct draining into the left venous angle now each of these ducts
are fed into by lymphatic trunks now the three major trunks that are going to be supplying these
ducts are the Bronco mediastinal trunks which are coming up from the lungs through the mediastinum
of the thorax ascending superiorly they're also subclavian trunks which are bringing in lymph from
the upper limbs under the clavicle and jugular trunks which are returning lymph from the head and
neck and so we can see the coalescence of these trunks here feeding into the right lymphatic duct
and we can see the coalescence of these trunks here in addition to the thoracic duct which is
making its way up from the abdominal cavity on the left side now there are various organs which
comprised the lymphatic system and we could divide these up into both primary and secondary lymphatic
organs primary lymphatic organs are things like the thymus gland and red bone marrow or you might
a poetic connective tissue these are places of stem cell mitosis and immunocompetence meaning
stem cells which would give rise to blood cells are creating new blood cells and specialized
blood cells such as lymphocytes are gaining the ability to recognize antigens and react to them
secondary lymphatic organs such as the spleen and lymph nodes and nodules are simply places
where immune responses may be hosted among other functions the thymus gland is an interesting part
of the mediastinum so here we can see the thymus gland sitting within both the superior in the
anterior mediastinum the thymus gland itself is by lobed so there are two separate constituent
bodies of glandular material here and they're connected along the midline thymus gland is at
its greatest glandular mass approximately just beyond puberty and then it begins to diminish
it goes through a process known as fibrosis where that glandular material is replaced
by adipose connective tissue and that's why in older individuals that thymus gland appears as
two masses of thymic fat now the thymus gland has two portions to it there's an outer cortex
in an inner medulla that outer cortex is for t-cell selection and maturation meaning it's
here that t-cells are really going through their early stages of nascent development up through
becoming fully immuno competent and then they migrate to the medulla where they may be further
selected such that they're not autoreactive or would have an immune response against an
individual's own cells we can see the thymic fat here in this image so it's sitting just below the
root of the neck medial to the lungs and anterior to the heart encased in its pericardium and this
particular individual was of sufficiently advanced age that the thymus gland is now thymic fat lymph
nodes and nodules are secondary lymphatic organs the difference between the two is an outermost
capsule so lymph nodes have a connective tissue capsule that surrounds them whereas lymph nodules
do not lymph nodes are clustered and those clusters of lymph nodes are typically named
for the anatomical region that they're serving and you can see that they are fed by a ferrant
lymphatic vessels bringing lymph and its contents into the lymph node and within the lymph node we
bring antigens and antigen presenting cells into contact with T cells and B cells or lymphocytes
such that a host can mount an immune response afterwards these nodes are drained via efferent
lymphatic vessels that are going to coalesce into various lymphatic trunks the nodules lack
that connective tissue capsule typically we refer to these as malt or mucosal associated lymphoid
tissues you're probably already familiar with some of this such as the tonsils that surround
your pharynx so these are supporting immune responses in the upper pharynx or the throat and
they're also specialized patches of these nodules embedded within the mucosa of the GI specifically
the small intestine called peyer's patches which brings the immune system into intimate contact
with that gastro intestinal mucosa so that it may best mount an immune response against any
pathogens making their way in through the GI and they can also be present to help collect
and then ultimately transport any fatty acids up to the liver and then finally we have the spleen
the spleen is the body's largest collection of lymphatic tissue it's located in the left
hypochondriac region which is that area inferior to the diaphragm but still surrounded in part by
the bony ribcage the spleen consists of two sets of tissues which have too drastically different
functions the white pulp is where lymphocytes are going to act or we can have immune function the
red pulp is what best serves the cardiovascular system so it's working for filtering erythrocytes
helping to store platelets and at different times in development even helping to generate
new blood cells now here we can see that there are different impressions for the spleen because
in that left hypochondriac region it's going to come into contact with several different organs
so we can see here a gastric impression formed from the body of the stomach we can also see a
renal impression from the left kidney we can see a colic impression from the large intestine here
and we can see that the spleen is served by two major vessels there's the splenic artery which
is a branch of the celiac trunk which is a very torturous or curvy artery that enters the spleen
at the hilum and then blood is drained from the spleen via the splenic vein which is one of two
veins the other being the superior mesenteric vein which comes together to form the hepatic
portal vein that transports blood from the GI to the liver and finally we can see the spleen
in situ in academic image so the spleen is located here we can see just a hint of that splenic artery
along with the stomach the left kidney is hidden by this connective tissue here and we can see the
large intestine and that splenic flexure of the transverse colon there we've talked a little bit
about the large picture approach to how lymph is drained from the body some of the major players
with regards to the organs of the lymphatic system and some of its functions in later
lessons we're going to talk about the patterns of lymph drainage in each region of the body