Lymphatic System: Crash Course A&P #44

Lymphatic System: Crash Course A&P #44

Let’s say you’re at the airport. You’re
waiting in line to get through security. You’re in your socks, in public, and you’re
wrestling with those plastic bins, and people are yelling at you about dumping liquids and
taking your laptop out your bag. But even with a certain amount of chaos, the
line moves pretty quickly. I mean, it should. Theoretically. Because really, everyone has the same goal:
to get to where they need to be. Now, you probably think that I’m setting you
up to talk about stress or anxiety or something. But I am not! Instead, I want you to imagine that security
line as being like your blood, moving through your high-pressured circulatory system. And you, my friend, are not just some impatient
traveler in a hurry to catch the next plane to Seattle. You are a bit of blood plasma. And the biggest concern of everyone in your
queue is just to get delivered to their destination. But the problem with rushing stuff through
a blood vessel — or a security line — is that if it moves too fast, you run the risk
that something bad might get through. So, in the case of the line at the airport,
every now and then, the security people funnel some random people into a slower line for
a full pat down and bag check. And, that is kinda what your lymphatic system
does. It takes up some extra fluid and, while it’s ultimately helping it get to its destination
— it runs a background check to make sure it’s legit. It may not be as well-known as some of your
more popular organ systems, but your lymphatic system quietly plays a vital supporting role
to both your cardiovascular and immune systems. For one thing, it maintains your homeostasis
by eventually returning most of the fluid that has been diverted back into your blood. Which is good, because if it didn’t, your
ankles would swell up like balloons, your lungs would fill with fluid, and your blood
volume and pressure would drop to the point where your body would just give up and you
die. But the lymphatic system isn’t just another
security line. It also has a series of checkpoints that are staffed by special security officers that have
the ability to take care of small infections on the spot. Or if they really don’t like the looks of
what they’ve found, they can alert the whole immune system to take it down. So, for keeping your blood-volume levels where
they need to be, for keeping you from collapsing from low blood pressure, and for preventing
you from dying from a staph infection every time you scrape your elbow, you have to thank
the unsung hero of your anatomy: your lymphatic system. Structurally speaking, your lymphatic system
consists of three main parts: The first is just …your lymph. It’s a watery fluid that flows through your
lymphatic system. Much of your lymph starts out as blood plasma
that gets forced out of your capillaries, way down in the capillary beds, where the
leakage helps the exchange of nutrients and gases between the blood in the capillaries
and the hungry cells in your tissues. The blood capillaries reabsorb some of the
fluid, but a lot gets left behind. So, much of the rest of your lymphatic system works
to soak it up and get it back to where it needs to go, inspecting it along the way. For example, you have a network of lymphatic
vessels that help reabsorb the fluid, and about 600 or 700 lymph nodes, which are basically
checkpoints that monitor and cleanse the lymph as it filters through. Then there are special lymphoid organs, like
the spleen, thymus, adenoids, and tonsils, as well as other lymphoid tissues throughout
the body. Some of these organs and tissues house special
defensive cells of the immune system to fight infection by gobbling up bacteria and other
harmful antigens — all of which we’ll get into a lot more in upcoming lessons. Others,
like the thymus and spleen, provide a nursery for maturing immune cells called lymphocytes. But to understand the special supporting role
that your lymphatic system plays in your body, let’s start with its origins — in the capillary
beds of your circulatory system. You’ll recall that these beds are where
the capillaries carry blood from your arterioles — and your arteries before that — and feed blood
into your venules — and eventually your veins. This is where the transfer of nutrients and
waste takes place, as blood pressures force plasma out of the arteriole end of the capillaries
and into the interstitial fluid between the cells of whatever tissue you happen to be
in. And most of that fluid gets drawn right
back into the capillaries on the venous end, thanks to osmotic pressure. But some is left behind. Of the 20 liters
a day that’s forced through the arteriolar end of all the capillaries all over your body,
only 17 liters is taken back up by the venous end. Those other 3 liters? That becomes your lymph. It’s almost immediately picked up by nearby
lymphatic capillaries that wind their way in and among the blood capillaries, and they’re
really well-suited for the job. Lymphatic capillaries are made of loosely
overlapping, endothelial cells that look kind of like roofing shingles, forming little flap-like
valves that only open in one direction. So when the pressure in the interstitial space
becomes greater than the pressure inside the lymphatic capillary, the flaps push open and
take in fluid to relieve the pressure. Once the fluid is inside a lymphatic capillary,
we can officially call it lymph. Then it flows through successively larger lymphatic vessels
to collecting vessels and then to larger trunks and finally, into one of two big ducts that
feed back into the lowest pressure area of the circulatory system. The right lymphatic duct drains all the lymph
collected from the upper right area of the torso, as well as the right arm, and the right
sides of the head and thorax, and feeds them all into the internal jugular vein. The larger thoracic duct takes lymph from
the rest of the body, and dumps it into the subclavian vein. Overall, these vessels work a lot like your
veins do. They operate under very low pressure, have a series of valves that prevent backflow,
and are helped along a bit by smooth muscle in the vessel walls that keep the fluid moving. OK, so the lymphatic system takes extra fluid
that’s squeezed out of the blood capillaries and basically mops it up. That sounds handy.
But, as a living thing that wants to stay alive, what’s in it for you, exactly? Well, remember: We’re talking about recovering
3 liters of blood fluid per day — that’s more than half of your total blood volume. If that weren’t returned to your circulatory
system, you’d be looking at a serious drop in blood pressure, and little to no oxygen
delivery, or waste pick up. Plus, any blockage in the lymph system — like
from a tumor that obstructs one of your vessels — can be really dangerous, resulting in edema,
or swelling, that can constrain blood flow and lead to serious complications. And finally: Don’t forget that your lymph also plays
a key role in the function of your immune system. Say you scrape your elbow, and some bad stuff
— like the staphylococcus bacteria that’s covering your entire body right now — infiltrates
some of the loose areolar connective tissue under your skin. Since that tissue is full of interstitial
fluid that drains into your lymphatics, which ultimately drain to your heart, you’re going
to want to vanquish those bad guys before they have a chance to wreak any havoc. What ever will you do? Well, this is where your lymph nodes come
in. Your body’s main lymphoid organs, the lymph
nodes are where your lymph gets close and regular inspection by its resident immune
cells, lymphocytes. Depending on what kind of troublemaker they
find in the fluid, the lymphocytes might trigger the release of resident macrophages to attack
unwanted microorganisms. Or they might activate the general immune system outside of the node,
if they need extra support. The details of how that happens we will get
to next time, but for now just understand that lymphocytes are found in, and mature
in, the loose reticular connective tissue that makes up a large part of the nodes and
most of your other lymphoid organs. Now, if a node is overwhelmed by whatever
invader it’s trying to quell, it may become inflamed.
You can actually feel some of your nodes if you poke around the sides of your neck. They feel like little bumps…yeah, there
they are. And noticeably enlarged lymph nodes are often
an early diagnostic sign of disease or infection, which is why doctors are always feeling around
under your jawline during check-ups. But your lymph nodes aren’t the system’s
only checkpoints. You’ve also got a few special outposts placed at strategic entry
points to particularly sensitive tissues, like the those in the respiratory and digestive
tracts. These are called mucosa-associated lymphoid
tissues, or MALTs, because they can be found in mucous membranes around the body, outside
of the lymphatic vessels. Your tonsils are some of the largest collections
of these tissues, which together form a ring around the entrance of the pharynx. There
they can inspect everything you eat and breathe and try to remove any pathogens before they
enter the GI tract or lungs. It’s a pretty big job, actually, which is
why sore throats and swollen tonsils are a common sign of a cold or other infection. Another collection of MALTs, called Peyer’s
patches, are in the distal portion of the small intestine, providing another check point
along the GI tract. And contrary to popular myth, your appendix
is not useless, because it too contains a bunch of lymphoid tissue and is conveniently
located where it can destroy any remaining bacteria before it can breach the intestinal
wall during absorption. Exactly how your lymph and immune cells detect
and destroy the unwanted visitors that might otherwise kill you is what we’re gonna be
talking about for the remainder of this course. But for now you learned how your unsung lymphatic
system supports cardiovascular function by collecting, filtering, and returning interstitial
fluid back into the bloodstream via a system of lymphatic vessels. We also talked about
the system’s major role in fighting off infection, and how lymph nodes, and other
lymphoid organs, and MALT areas house antigen-attacking lymphocytes that provide crucial support to
the immune system. Thank you to our Headmaster of Learning, Linnea
Boyev, and thank you to all of our Patreon patrons whose monthly contributions help make
Crash Course possible, not only for themselves, but for everybody, everywhere. If you like
Crash Course and want to help us keep making videos like this one, you can go to This episode was filmed in the Doctor Cheryl
C. Kinney Crash Course Studio, it was written by Kathleen Yale, the script was edited by
Blake de Pastino, and our consultant is Dr. Brandon Jackson. It was directed by Nicholas
Jenkins, edited by Nicole Sweeney, our sound designer is Michael Aranda, and the Graphics
team is Thought Cafe.

100 Replies to “Lymphatic System: Crash Course A&P #44”

  1. Dunno why I watch these guys vids, every time I leave more confused than before, so many concepts mixed into one spoken at the speed of light

  2. i have to do an assignment on the lymphatic system so this is a lifesaver bc like nothing i find makes sense so uh cheers

  3. at 2:00 I thought it was done, who else thought that too. Oh wait no body cause this will be the 0.0000001% of people who actually look at the most recent comment and the other 99.999999% just looking at the top comments.

  4. I have a two disease first one lymphatic system second one varicose veins. How to remove it?
    If have any recovery options suggest me.

  5. People say you talk too fast. But i think you should never slow down. I always sleep in slow talking lectures and sometimes have to put the speed at 1.25 but crash course you have done it for me. Thanks a bunch

  6. I assure everyone here, my lymphatic system does a hell of a lot more to keep me safe then the Transportation Security Administration

  7. I watch CrashCourse videos when beginning a new chapter as a preview. Then I read the chapter for the detailed bits. Finally I re-watch the videos to review before taking the practice tests and doing the study questions. Sometimes, I will watch them a third time,just before taking the chapter test/quiz. Is that too much? 😉

  8. I have lymph nodes literally all over me. So far I counted 14 lymph nodes that are enlarged, one of them keeps growing so I had a ultrasound on it and came back abnormal so I have a appointment with a hematologist on May 6. I recently found one in my ankles never heard of them being there. Has anyone gotten them in the ankles ? ( my blood count is stable)

  9. I love how before I watched this series I thought that your spleen was useless, I can learn so much from you hank

  10. I have lymphedema in my right leg. This is … um. Interesting. My guard in my right leg is an idiot, and there is no back up.

  11. I simply don't like you! Too much distraction too many words that are jammed in each other and you simply annoy me with your hyperactive energy!

  12. How long will it take cured after ankle surgery? Can you able to give me any guidance for swelling on ankle after the surgery.

  13. These Videos are a great help, I wish there were some for my Mircobiology course. They are a big help for visual learners like me.

  14. Pee is edible so the stupid disease gets lured by the alluring smell of smee and then surprise pissed away Jesus Christ that was just piss in my boob why did you cut off my nipple.

  15. lymphatic fluid DOES NOT RECYCLE fluid. Its passed through the kidneys ur supposed to see white sediment in urine

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