The lymphatic system comes up a lot in things related to cancer. It never showed up in high school biology or textbooks. I know that it involves the fluid known as ‘lymph’ but I don’t really understand what lymph is even after researching it.
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The ELI5 is that it’s because the circulatory system is complex and the immune system is even more complex. You’d need courses in both before actually understanding what the lymph system is doing. Of course unless you’re satisfied with “the lymph system is an important part of the immune system, involving parts where immune cells are trained and proliferated”.
Think of the lymphatic system like a highway for your immune system. It’s a network of tiny tubes and nodes (small structures) that carry a fluid called lymph around your body. Lymph is a clear fluid that has white blood cells to fight infections. This system helps remove waste, toxins, and unwanted materials from our body.
It’s not as well-known because it’s complex and not as directly related to everyday functions like breathing or digestion. But it’s super important for keeping us healthy by defending against diseases!
The lymphatic system is a second circulatory system of sorts. You may know of the main blood circulation as a closed loop (heart > artery > tissue > vein > repeat, very broadly speaking) but this is not *entirely* true; the capillaries allow some fluid to leak out into surrounding tissue, because they have pores and the pressure in the capillaries is slightly higher than outside.
At that point the fluid, basically blood minus cells and large proteins, is known as extracellular fluid, and it still has nutrients and whatever else dissolved in it that get passed along to the tissue. But it needs to go somewhere again, or fluid would just build up in the tissue.
This is where the lymphatics come in. The average pressure inside lymph capillaries is a little lower than in the tissue, and the capillary walls are also leaky (but one-way!), so extracellular fluid drains into these little vessels. At that point, the fluid is referred to as lymph. These vessels will ultimately feed back into the main blood circulation, completing the loop.
[Here’s an image](https://upload.wikimedia.org/wikipedia/commons/1/19/Illu_lymph_capillary.png) to help visualize this.
So that’s one key purpose of the lymphatics; fluid drainage. You also asked about cancer, which is connected to its other function; immunity.
Stuff dissolved in the blood comes along in the extracellular fluid, plus whatever cells of the tissues secrete into it, and that all gets drained into the lymphatics. This is an extremely useful property to monitor what goes on in that tissue; you can compare it to real-life sewers from which researchers can take samples to measure anything from pathogens to drug metabolites, and something similar happens in the body where these lymphatic vessels connect to *lymph nodes*. These are hotspots for cells of the immune system, who gather there either to sample the passing lymph themselves or wait for specialized cells that travel through lymph ducts to bring samples right to them. Going into this any further would be out of scope, but suffice it to say that immune cells are key in surveilling and controlling cancer, and the lymph nodes are a critically important site where signals and information get exchanged between immune cells.
On top of that, the lymphatics are also just another circulatory system, so a metastatic cancer that happens to grow into a lymph vessel can be spread that way much like it would if it had grown into a blood vessel.
The lymphatic system is an odd beast for sure! It is responsible for the trafficking of your immune cells, which is why you hear about it when people talk about cancer. It is not always clear, but most of the time is. The times it’s not clear is is milky white, because they lymph also works with your digestive system to move Fat around. After a high fat meal, you lymph turns milky white. The main trafficking molecule needed to move fat around is call a Chylomicron and oddly enough, the main portal for dumping these molecules into the blood stream via the Thoracic duct. Yep you heard that right, fat is dumped into your blood stream right next to your heart. You never hear about chylomicron when it comes to heart disease either. Make you wonder why not?
Take a look at once upon a time… Life. The series is great. Sure, it is for kids but we watched some episodes in biology class in school.
Anybody taking A&P will have to learn about it but it requires some foundational inderstanding to help. If you mean generally why it’s not talked about with kids that’s probably because it’s glossed over as ‘The Immune system’ to help with understanding. Similar to how when a child breaks a bone you talk about how it will need to heal in a cast to get better and become stronger, not that there’s a 4 stage process that involves multiple types of cells like fibroblasts, osteoclasts, etc.
There’s a lot of posts saying it’s a highway for the immune system. This isn’t really the case. Your immune system is everywhere and a lot of your immune system is inherently part of your circulatory system.
At its most fundamental, lymph is there to collect fluid that leaves your blood vessels. Water leaves your blood vessels to go into your tissues. When there’s a bit too much it has to go back to the blood and it does through your lymphatic system.
Because the lymph system just passively pushes things it’s a great place to park immune cells. They hang out in your lymph nodes waiting to detect any issues with your tissues from the fluid passing through.
In the end it all gets dumped back in your blood near your heart for recirculation.
Without the lymphatic system, your tissues would swell up super easy, and your immune system wouldn’t be as effective.
The lymphatic system relates to the circulatory system, it has a role in combating infection and maintaining fluid balance https://youtu.be/FPBxhPFy22o
If you need it explained for kids, here’s a good video. I swear I didn’t learn any of this in high school and this blew me away.
[https://www.youtube.com/watch?v=I7orwMgTQ5I](https://www.youtube.com/watch?v=I7orwMgTQ5I)
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