Lymphatic System

When learning about the body systems, I’ve  always found there to be one system that is kind of clothed in mystery. And before I tell you  which body system this is…in case you didn’t see the title… I want to give you a little background  to why I think there is some mystery to this. If you look up, “How many body systems are there?

”  you actually can get different answers. And a lot of that is based on how general or detailed  you want to be. We go through 11 major body systems but as we emphasize, systems don’t work in  isolation so for example you might read a list of body systems where they list musculoskeletal  system, which is the combination of muscular and skeletal.

Or you might have a system  named that can be part of another system: for example, you might hear urinary system,  which is part of the excretory system. Anyway, as for the system that I mentioned  that has always been this one that never really got its 5 minutes of fame when I  was learning biology: it’s the lymphatic system. It can be because it’s common to lump  lymphatic with immune.

Or it is often phrased that the lymphatic system is a major part of  the immune system. But however it’s phrased, the lymphatic system still deserves its own video. So let’s talk about lymph.

To understand lymph: we  must understand interstitial fluid. Interstitial fluid is the fluid that you find outside of cells  – between cells- surrounding cells. This fluid can be there in the first place because of leakage of  fluid from blood capillaries.

Most of this fluid gets reabsorbed by blood capillaries. But some  of it doesn’t. The fluid that doesn’t and will go to the lymphatic system is known as lymph. 

It’s derived from blood plasma. Lymph can have many things in it too: proteins and lipids  for example. In fact, your small intestine uses lymph in the lymphatic system to get some  lipids and lipid soluble vitamins to the blood.

Lymph travels in your lymphatic system: a whole  network of lymphatic capillaries and vessels and ducts and nodes. Lymph can enter the system  in lymphatic capillaries. You’ll find lymphatic capillaries in almost every tissue in your body. 

Lymphatic capillaries open into larger lymphatic vessels. We should note that this traveling  of lymph in these lymphatic capillaries and vessels isn’t due to the heart that you’d  find in the circulatory system. Actually, much of the movement of lymph is thanks to your  own body’s movements from skeletal muscle – and also contractions of smooth muscle that can  line lymphatic vessels and other structures.

So, from lymphatic vessels we can go to lymphatic  ducts. There are two: the right lymphatic duct and the thoracic duct. The right lymphatic duct takes  lymph from the upper right side of your body.

And the thoracic duct takes lymph from everywhere  else. A little unequal there on the workflow: the thoracic duct takes on a lot more. So,  what happens in a lymphatic duct?

The ducts are where the lymph will drain. And they drain  to veins, specifically subclavian veins in the neck region. That means, the lymph gets  returned to the circulatory system.

So, you can definitely say the lymphatic system  works closely with the circulatory system. In our body systems overview video, we  mention that the lymphatic system collects, filters, and returns lymph to the  blood and has a major function in that it aids in immune function. So  we got the collect and return part: what about the whole filter part?

And  the aiding in immune function part? Enter the nodes: lymph nodes. They’re found in  many parts of your body and get a lot of credit for that filtering part.

Filtering out components  that can be found in the lymph that we haven’t mentioned yet like cellular debris and also  pathogens like bacteria and viruses. You’ll find immune cells called lymphocytes hanging out in  the lymph nodes. Lymphocytes are white blood cells involved in your immune system that specifically  target pathogens; lymphocytes can include B and T cells.

Other immune cells are also present in  the lymph node such as macrophages. While they’re not lymphocytes, macrophages are still part of the  immune system, and they’re just waiting to ingest a pathogen that may be lurking in the lymph. Lymph  nodes are something many people are familiar with, because when someone becomes ill from  some pathogens, lymph nodes can swell.

Lymph nodes are an area where many immune  system battles can occur. But lymph nodes aren’t the only type of lymphatic organ;  there are other lymphatic organs and tissues. There’s the spleen.

Sitting behind the stomach  in the upper left quadrant of the abdomen, the spleen is an organ that has high blood flow to it  and it also holds a lot of blood. So if this area of the body experiences trauma causing the spleen  to rupture, it can quickly become an emergency. The spleen has red pulp where damaged or old red  blood cells can be filtered as well as an area for nonspecific immune response and white pulp is  where a lot of the B and T cell action occurs.

There is lymphatic tissue known as tonsils.  Often when people are thinking of “tonsils,” they’re thinking specifically of palatine  tonsils, which you’ll find in the back of the throat. But that’s just one set of 4 total  sets of tonsils.

So with there being 4 sets: you have palatine tonsils, pharyngeal tonsils  (those are the ones that are sometimes called adenoids when they get swollen), lingual tonsils,  and tubal tonsils. Because tonsils are in that general area where breathing and eating  happen – this is kind of a prime location. Pathogens that encounter the tonsils will  be met with macrophages and lymphocytes.

Now the lymphoid organ and tissue structures  we’ve mentioned so far: lymph nodes, spleen, tonsils: those are considered secondary lymphoid  organs or tissues because while lymphocytes are taking action in them, the lymphocytes  didn’t develop from them. That’s not where the B and T cells – the lymphocytes-  came from. Bone marrow and the thymus are considered primary lymphoid organs.

Specifically,  B cells develop and mature in red bone marrow. T cells start out in the red bone marrow but  they mature in the thymus. The thymus is an interesting organ.

Before puberty, the thymus  is especially active as an organ for T cell maturity. As a person ages, the thymus starts  to shrink down and its activity decreases. So, let’s recap what we talked  about.

We talked about lymph: what it is and how it travels in lymphatic  capillaries and vessels and how it drains in ducts to return to the circulatory system. We  talked about how cellular debris and pathogens can be filtered from lymph through secondary  lymphoid organs and tissues like lymph nodes, spleen, and tonsils. We mentioned those structures  have immune cells like macrophages or lymphocytes like B and T cells.

We mentioned those  lymphocytes themselves start and mature in primary lymphoid organs; primary lymphoid  organs include the bone marrow and the thymus. Before we end, what happens if the lymphatic  system does not function as it should? If this system is not functioning well, the  traveling and draining of lymph can be compromised and potentially lymph can  collect in tissues where it shouldn’t: leading to swelling.

This swelling  can be referred to as lymphedema. Many different conditions that affect the  lymphatic system can cause lymphedema. In a disease called lymphatic filariasis,  a parasite can be the cause of lymphedema.

Specifically a microscopic worm, or if you want  to get a bit more specific from our animal video, a nematode. These nematodes can be  transmitted to humans by a mosquito; the mosquito is the vector. Once the nematodes  are inside the body, they can grow and mature into adulthood in the vessels of the lymphatic  system.

The damage this can cause can lead to lymphedema in some individuals. Thankfully there  are treatments that can target the parasites and there are more methods being explored for  controlling the mosquitoes that are acting as vectors –learn more about this disease in  the further reading of our description. Well, that’s it for the Amoeba Sisters,  and we remind you to stay curious.