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.
