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.
In: 104
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.
Latest Answers