Lymphatic System: Crash Course Anatomy & Physiology #44

Summary

This script creatively compares the lymphatic system to an airport security line, emphasizing its crucial role in maintaining homeostasis and supporting the immune system. It explains how lymph, a fluid derived from blood plasma, is collected and filtered through lymphatic vessels and nodes, which act as checkpoints for infections. The lymphatic system's ability to return fluid to the bloodstream and its role in nurturing immune cells are highlighted, illustrating its vital function in overall health.

Takeaways

• 🛂 The airport security line is used as a metaphor for the lymphatic system, emphasizing the importance of both in filtering and ensuring safety.
• 🩸 The lymphatic system is crucial for maintaining homeostasis by returning most of the fluid that has been diverted back into the blood.
• 🚫 If the lymphatic system didn't function properly, it could lead to severe swelling and potentially fatal drops in blood volume and pressure.
• 🛡️ The lymphatic system has checkpoints, like lymph nodes, that inspect and cleanse the lymph, playing a role in the immune response.
• 🚨 Lymph nodes can alert the immune system to threats and are a key part of the body's defense against infections.
• 🌐 The lymphatic system consists of lymph, a fluid that starts as blood plasma, and a network of vessels and nodes.
• 💧 Lymph is formed from the fluid that is forced out of the blood capillaries and not reabsorbed, amounting to about 3 liters per day.
• 🔄 Lymphatic vessels transport lymph through a one-way system with valves to prevent backflow, similar to veins.
• 🏭 Special lymphoid organs, such as the spleen and thymus, house immune cells and provide a maturation environment for lymphocytes.
• 🚨 Lymph nodes can become inflamed and enlarged in response to infection, serving as an early diagnostic sign for doctors.
• 🌐 Mucosa-associated lymphoid tissues (MALTs) are strategically placed to inspect and filter pathogens from entering sensitive areas like the respiratory and digestive tracts.

Q & A

What is the analogy used in the script to describe the movement of blood plasma through the circulatory system?

The script uses the analogy of a security line at an airport to describe the movement of blood plasma through the circulatory system.

What is the primary function of the lymphatic system in relation to the cardiovascular system?

The primary function of the lymphatic system in relation to the cardiovascular system is to maintain homeostasis by returning most of the fluid that has been diverted back into the blood, preventing swelling and maintaining blood volume and pressure.

How does the lymphatic system assist the immune system?

The lymphatic system assists the immune system by having a series of checkpoints, or lymph nodes, that monitor and cleanse the lymph, and by housing special defensive cells that can fight infection by gobbling up bacteria and other harmful antigens.

What are the three main parts of the lymphatic system?

The three main parts of the lymphatic system are the lymph itself, a network of lymphatic vessels, and special lymphoid organs like the spleen, thymus, adenoids, and tonsils.

What happens to the blood plasma that gets forced out of the capillaries and is not reabsorbed?

The blood plasma that gets forced out of the capillaries and is not reabsorbed becomes lymph, which is then picked up by nearby lymphatic capillaries.

What is the role of lymphatic capillaries in the lymphatic system?

Lymphatic capillaries are responsible for picking up the fluid that has been forced out of the blood capillaries. They have flap-like valves that open in one direction to take in fluid when the pressure in the interstitial space is greater than the pressure inside the lymphatic capillary.

What are the two major ducts that return lymph to the circulatory system?

The two major ducts that return lymph to the circulatory system are the right lymphatic duct and the thoracic duct.

How does the lymphatic system help prevent serious drops in blood pressure?

The lymphatic system helps prevent serious drops in blood pressure by recovering about 3 liters of blood fluid per day and returning it to the circulatory system, ensuring adequate blood volume and pressure for oxygen delivery and waste pickup.

What is the significance of lymph nodes in the immune response?

Lymph nodes are significant in the immune response as they provide a site for lymph to be inspected by immune cells, lymphocytes, which can trigger the release of macrophages to attack unwanted microorganisms or activate the general immune system if needed.

What are MALTs and where are they typically found?

MALTs, or mucosa-associated lymphoid tissues, are special outposts of the lymphatic system found in mucous membranes around the body, outside of the lymphatic vessels. They serve as checkpoints to inspect and remove pathogens, such as in the tonsils and Peyer's patches in the small intestine.

Why is the appendix considered important for the immune system despite popular myth?

Contrary to popular myth, the appendix is important for the immune system because it contains lymphoid tissue and is strategically located to destroy bacteria before they can breach the intestinal wall during absorption.

Outlines

00:00

🛂 Airport Security Line Metaphor for Lymphatic System

The paragraph uses the analogy of an airport security line to explain the function of the lymphatic system. It describes the chaotic yet efficient process of people moving through security as similar to blood plasma moving through the circulatory system. The lymphatic system is likened to a security checkpoint that ensures fluid and cells are legitimate before they re-enter the bloodstream. The paragraph highlights the lymphatic system's role in maintaining homeostasis by returning diverted fluid to the blood, preventing life-threatening swelling and drops in blood pressure. It also emphasizes the lymphatic system's lesser-known but crucial function in the immune response, with lymph nodes acting as checkpoints to detect and neutralize infections.

05:04

💧 The Lymphatic System's Vital Role in Health

This paragraph delves into the importance of the lymphatic system in maintaining life by recovering over half of the body's total blood volume daily. It explains the consequences of not returning this fluid to the circulatory system, such as severe drops in blood pressure and oxygen delivery issues. The paragraph also discusses the lymphatic system's role in the immune system, particularly in dealing with infections like staph bacteria. Lymph nodes are described as the main lymphoid organs where lymph is inspected by immune cells called lymphocytes. These cells can trigger a local immune response or alert the general immune system if needed. The paragraph also introduces other lymphoid organs and tissues, including MALTs and the appendix, which are strategically placed to protect sensitive tissues from pathogens.

Keywords

💡Circulatory System

The circulatory system is the body's 'transport' network, responsible for circulating blood to supply oxygen and nutrients to the body's cells and to remove carbon dioxide and other waste products. In the video, the circulatory system is likened to a busy airport security line, emphasizing the high-pressure environment in which it operates and the importance of its function in maintaining homeostasis.

💡Lymphatic System

The lymphatic system is a secondary network of vessels that complements the circulatory system by returning interstitial fluid to the bloodstream, maintaining fluid balance, and supporting the immune system. The video script describes the lymphatic system as an 'unsung hero' of the body, highlighting its vital yet often overlooked role in health.

💡Blood Plasma

Blood plasma is the liquid component of blood in which cells are suspended. It is primarily composed of water, proteins, electrolytes, and other dissolved substances. In the script, blood plasma is used as a metaphor for the viewer, drawing a parallel between the movement of plasma through the body and the movement of people through an airport security line.

💡Lymph Nodes

Lymph nodes are small, bean-shaped structures that act as 'checkpoints' in the lymphatic system, filtering the lymph and housing immune cells. They are crucial for the body's defense against pathogens. The video script uses the analogy of a security pat-down to explain how lymph nodes inspect the lymph for harmful substances.

💡Lymph

Lymph is a clear fluid that travels through the lymphatic system, carrying waste products away from tissues and returning them to the bloodstream. It originates from blood plasma that has seeped out of capillaries. The script describes lymph as a 'watery fluid' that is essential for the body's fluid balance and immune response.

💡Homeostasis

Homeostasis refers to the body's ability to maintain a stable internal environment despite changes in external conditions. The lymphatic system plays a key role in this by regulating fluid balance, as explained in the script, ensuring that the body's tissues do not become overly swollen or starved of necessary fluids.

💡Immune System

The immune system is a complex network of cells, tissues, and organs that work together to defend the body against pathogens and foreign substances. The video script highlights the lymphatic system's integral role in supporting the immune system, particularly through the function of lymph nodes and other lymphoid tissues.

💡Lymphatic Vessels

Lymphatic vessels are the conduits through which lymph flows. They are similar to blood vessels but operate under lower pressure and have unique features, such as one-way valves, to facilitate the movement of lymph. The script describes these vessels as essential for 'mopping up' excess fluid and transporting it back to the circulatory system.

💡Lymphoid Organs

Lymphoid organs are structures that are part of the lymphatic system and play a key role in the immune response. Examples include the spleen, thymus, adenoids, and tonsils. The script explains that these organs house immune cells and are involved in the maturation of lymphocytes, which are critical for fighting infections.

💡MALT (Mucosa-Associated Lymphoid Tissue)

MALT refers to lymphoid tissues found in mucous membranes throughout the body. They serve as the first line of defense against pathogens entering the body through the respiratory and digestive tracts. The script mentions tonsils and Peyer's patches as examples of MALTs, emphasizing their strategic placement for immune surveillance.

💡Edema

Edema is the swelling caused by an excess of fluid in the body's tissues. It can occur if the lymphatic system is unable to properly return interstitial fluid to the bloodstream. The script warns that blockages in the lymphatic system can lead to edema, which can restrict blood flow and cause serious health complications.

Highlights

The airport security line is likened to the blood moving through the high-pressure circulatory system, with the lymphatic system acting as a security checkpoint.

The lymphatic system plays a vital supporting role to the cardiovascular and immune systems, maintaining homeostasis by returning fluid to the blood.

If the lymphatic system fails to return fluid, it could lead to severe swelling, low blood pressure, and potentially death.

The lymphatic system has checkpoints that can handle small infections and alert the immune system to larger threats.

The lymphatic system consists of lymph, lymphatic vessels, lymph nodes, and lymphoid organs, each with specific roles in fluid reabsorption and immune response.

Lymph nodes are essential in filtering lymph and housing immune cells that can respond to infections.

Lymph is initially blood plasma that is forced out of capillaries and becomes the fluid that the lymphatic system processes.

Lymphatic capillaries have unique flap-like valves that allow one-way flow to collect interstitial fluid as lymph.

The right lymphatic duct and thoracic duct are the main pathways for lymph to return to the circulatory system.

The lymphatic system is crucial for maintaining blood volume and preventing drops in blood pressure.

Blockages in the lymphatic system can lead to dangerous edema and complications.

Lymph nodes are the primary sites for immune cell activity and can become inflamed in response to infection.

Mucosa-associated lymphoid tissues (MALTs) are positioned at strategic entry points to sensitive tissues for initial immune response.

The tonsils and appendix are part of the MALTs, playing a role in inspecting and removing pathogens from the body.

Lymphocytes within lymph nodes and lymphoid organs are key to the immune system's ability to detect and destroy pathogens.

The lymphatic system's role in immune function is integral to preventing infections from causing severe illness.

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Transcripts

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 patreon.com/crashcourse.

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.