Introduction to the Lymphatic System

Introduction to the Lymphatic System


“Lymph” means “clear water” in Latin,
and it describes the fluid that flows through the lymphatic vessels and lymph nodes which
make up the lymphatic system. The three major roles of the lymphatic system
– the reason we need it in the first place – are that it returns fluid from the tissues
back to the heart, it helps large molecules like hormones and lipids enter the blood,
and it helps with immune surveillance to keep infections from running amok. So, let’s take a closer look at lymph and
where it comes from. The blood in the arteries is under a lot of
pressure because it needs to reach every little nook and cranny of the body. The arteries branch out into narrower and
narrower arteries, and then arterioles, and finally gets to the capillaries – which have
walls that are only one cell thick and are slightly porous. Red blood cells are too big to fit through
capillary pores, but small proteins like albumin and fluid can make it through. Every day 20 liters of fluid water and protein
– seep out of the capillaries and becomes part of the interstitial fluid between cells. About 17 liters gets quickly reabsorbed right
back into the capillaries, but that leaves 3 liters of fluid behind in
the tissues each day. This 3 liters of fluid needs to find a way
back into the blood so that the body’s interstitial fluid volume and blood volume both stay constant
over time. That’s where the lymphatic vessels, or lymphatics,
come in: they collect excess interstitial fluid and return it to the blood. Once the interstitial fluid is in the lymphatic
vessels, it’s called lymph. Now – you may be wondering how there can be
20 liters of fluid seeping out each day if the blood volume is only 5 liters, but remember
that the 5 liters is constantly in motion and that it gets recycled over and over in
a single day. Unlike the circulatory system, the lymphatic
system isn’t a closed loop because fluid and proteins make their way into the microscopic
lymphatic capillaries, and all of the collected lymph is dumped into the veins. Lymphatic capillaries are the smallest lymphatic
vessels, and they’re located throughout the interstitial space. Lymphatic capillaries are extremely permeable
because their walls are made of endothelial cells that only loosely overlap, forming one-way
minivalves. These endothelial cells are anchored to structures
in the interstitial space by collagen filaments, which allows the lymphatic capillaries to
remain flexible but retain their overall shape. When the pressure in the interstitial space
is greater than the pressure in the lymphatic capillary, the endothelial minivalves open
up, allowing fluid to enter. When the pressure in the interstitial space
is less than the pressure in the lymphatic capillary, the endothelial minivalves are
pushed shut, keeping the lymph inside. Once the lymph is inside the lymphatic capillaries,
it travels through bigger and thicker-walled vessels, then trunks, and then ducts. There’s no pump pushing the lymph through
the lymphatic system; instead, smooth muscle in the lymph vessels reacts to the pulsing
of nearby arteries by squeezing to get things started, and then the squeezing of skeletal
muscles, which normally contract throughout the day, exert external pressure to keep the
lymph moving along eventually reaching a nearby lymphatic trunk. To keep the lymph from sliding backwards,
the lymphatic vessels have valves just like the veins. The lymphatic trunks are named after the regions
of the body that they drain the lymph from: two lumbar trunks, two bronchomediastinal
trunks, two subclavian trunks, and two jugular trunks, as well as one intestinal trunk. From there, the lymph is delivered to either
the right lymphatic duct which collects lymph from the right arm and the right side of the
head and chest, or the thoracic duct, which is much bigger and collects lymph from the
rest of the body. The right lymphatic duct dumps lymph into
the junction of the right jugular vein and the right subclavian vein, and the thoracic
duct dumps lymph into the same junction on the left side of the body. That particular spot is perfect because it’s
where the pressure is very low, making it much easier for the lymph to flow in. The lymphatic system has key advantages: for
example it can pick up larger molecules, like hormones, that are too large to get into the
capillaries, and get them into the bloodstream. The lymphatic system can also help get nutrients
to the tissues. For example, during a meal, fatty acids get
packaged into balls of fat called chylomicrons by the small intestine. But like the hormones, these are too large
to move across capillaries. Instead, the chylomicrons go into special
lymphatic vessels called lacteals, which get their name from the fact that the lymph that
flows through them looks like milk. The chylomicrons slowly make their way up
into the thoracic duct and get dumped into the venous blood. The lymphatic system also plays an important
role in immune function. Lymphoid organs remove foreign material from
the lymph to keep it from entering the bloodstream, and act as lookout points for the body’s
immune defenses. Some lymphoid organs are in the form of diffuse
lymphoid tissue, where they are just a loose arrangement of lymphoid cells and protein,
this is typical in the lining of the gastrointestinal and respiratory tract. Another type of lymphoid organ are lymph nodes,
which are tightly packed balls of lymphoid cells and protein. Hundreds of lymph nodes cluster along the
lymph vessels, each one a few millimeters to about 1–2 cm in size. When they’re concentrated along the lymph
trunks, you can feel them, especially in the neck, armpit, and groin. They can also be found in the intestinal wall,
where they’re called Peyer’s patches. When an infection gets into the tissue, it
can slip into a lymphatic capillary and move into a lymphatic vessel. Unfiltered lymph fluid drains into a nearby
lymph node where any pathogen or piece of pathogen is quickly detected by a dendritic
cell – a type of antigen-presenting cell that serves up pieces of anything in destroys to
other immune cells. In the lymph nodes, dendritic cells continuously
sample the lymph and present antigens that they come across to the B cells which are
a type of lymphocyte that can make antibodies. B cells are designed to only react to foreign
antigens, and if the dendritic cell presents something foreign, the B cell turns into a
plasma cells and starting cranking out antibodies which flow into the lymph exiting the lymph
node. There are also circulating T cells, which
are another type of lymphocyte that move between the lymph nodes, lymph, and blood on the lookout
for pathogens and infected or abnormal cells that have been tagged by antibodies. Another lymphoid organ is the spleen, which
is about the size of a fist, and sits on the left side of the body below the diaphragm
and on top of the stomach. The spleen has both white pulp and red pulp. The white pulp is where antibody-coated bacteria
are filtered out of circulation and antibodies are generated by B cells. In a sense, the white pulp of the spleen is
like a giant lymph node, although unlike a lymph node which receives unfiltered lymphatic
fluid, the spleen receives blood. The red pulp of the spleen is where old and
defective blood cells are destroyed and their parts – the hemoglobin, the heme chain, and
the iron – are either broken down or recycled. The spleen is also a helpful in that it keeps
a red blood cells and platelets available in case they are suddenly needed by the body. An organ that’s got your back in an emergency. Another lymphoid organ is the thymus, which
is in the upper part of the chest – just below where a necklace might lie. The thymus is most active in the neonatal
period and pre-adolescent years, and then slowly atrophies and gets replaced by fat
after puberty. The thymus is involved in the development
of T cells – making sure that any T cells that react to self-antigens, antigens that
are normally found in the body, are promptly destroyed. A final set of lymphoid organs worth mentioning
are the tonsils, which include the adenoid, tubal tonsils, palatine tonsils, and lingual
tonsils. Together they form a ring of lymphoid tissue
around the throat, and their main job is to trap pathogens from the food you eat and air
you inhale. All right, as a quick recap: the lymphatic
system refers to the one-way network of lymphatic vessels that allows lymph, a clear fluid that’s
squeezed out of the blood, to transport nutrients to the cells and act as a method of waste
removal. Lymph is cleansed at lymph nodes throughout
the lymphatic system, which play an important role in immune function. Thanks for watching! You can help support us by donating on patreon,
or subscribing to our channel, or telling your friends about us on social media.

100 Replies to “Introduction to the Lymphatic System”

  1. i studied a bout liymapatic system but l only remember the topic and lymphcities( white blood cells). 10Q for vid.

  2. In short this is a good presentation. Well, if possible please do a bit more picturial and descriptive about lymphatic system.

  3. amazing and concise video! very straightforward​ and clear … i always hated the lymphatic in medical school

  4. Don't the interstitial fluid enter the lymph capillaries first, before they branch out into lymphatic vessels?

  5. I've struggled to find a video that explains everything so clear just like my textbook but this is it! thank you so much !

  6. Do lymphatic drainage massages cause problems to the functioning of the lymphatic system ? For example the tanaka face massage ?

  7. Very true, college biology courses rarely teach anything on the lymphatic system. A very useful and informative video.

  8. i agree with you ! even in my nursing studies this wasnt given so much attention. then as i worked as a nurse, i couldnt figure out how they just simply cut it off when blockages starts building up. Im now practicing therapeutic lymphatic drainage massage and just with precise maneuver could do so much wonder to properly function again without pharmaceutical medication or under the knife procedures.

  9. You guys are blessings in diguise😇. Sincerely thank you for what you do😊😊👍🏻👍🏻👍🏻

  10. good video but i'm curious about what you mean when you say proteins escape the capillaries…this certainly happens during inflammation, but during normal circumstances there is not much in the way of protein loss through the capillaries to my understanding. also, fenestrated capillaries do occur in the GI tract and some other places, but not in all vascular beds. it might be worth noting this

  11. I have many tiny red dot in my throat and the end of my tongue…. And i have also like a mini balls like under my ear…. I felt pain in my chest sometimes… It is lymphatic problem?

  12. Exquisite Video: Sympathetic, Informative and Creative.  Lymph (Latin for "Clear Water") is a Distributory System of Lipids and Hormones and an "Immune Surveillance System."  The Interstitial System or the Space of Intersitium is the Active Site of the Lymphatic System with a Valvular Mechanism relying on Circulatory Pressure (Other Pressuregenics of the Body) for its Function (Capillary, Vessels, Trunks and Ducts Totally is Active Circulatory Morphology).   A Cardiologist has to always Factor In the Pressure Value of all the Blood Circulatory Factors along with the Lymph Pressure Circulatory Values amounting to much more than Standard Workload Projections of Today.  This is precisely the Reason why Combating Cardiopathies or Cardiac Disease (CDs) is currently a downward Spiral and The Leading Cause of Death in the United States (One MIllion People Die of Heart Diseases), a worrisome Epidemiology (A True Pandemic for Some).

  13. Osmosis is the best channel o have came across since I started med school, it's just amazingly helpful, short, the content is interesting not boring, the speaker speaks clearly which is amazing for non-native English speakers and the list go on….. Keep up the good work please you are just amazing

  14. 👌👌👌👌👌 much more educating compared to a doctor's prescribe medication. 🤗🤗🤗🤗😉

  15. This is awesome! Not bogged down with too much info but really informative. The illustrations are SPOT ON! So easy to understand! I get the lymph system now. Thank you !

  16. Thanks a lot man! Was going through the immunology system and found out this video which gave many more clear conception and its so easy to understand! Subscibed!

  17. Can anyone explain me how does 20L of plasma escapes through the capillary bed although the blood volume is 5 liters

  18. I can't remember learning anything about the Lymphatic system in k-12 education (between 1975-1987). My Japanese wife thinks I'm an idiot since I didn't know anything about it and how/why tumors form in the lymph nodes (or even where these nodes are)… So thank you for this introduction!

  19. Like seriouslly how can someone make this type of amazing videos to to easy to understand Thanks for making life easy 😍😍😍

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