The Lymphatic System’s Hidden Talents: Fat Transport, Lymph Clearance and Immunity.

This is the first post in a two part series on the Lymphatic System, click here for Part 2 (When The Flow Gets Blocked) to learn about what happens when this system stops working correctly.

Lymph nodes are a common enough medical term but what do they actually do? Did you know that an adult has about 800 lymph nodes in their body? These are part of the larger lymphatic system which also includes your bone marrow, thymus, spleen and your mucosa-associated lymphoid tissue.

Your lymphatic system plays three main roles in your body. It clears out a fluid called lymph, it plays a big role in your body’s immunity, and it transports fat to allow it to be used by your body.

Role 1: Lymph

In order for your blood to deliver oxygen and nutrients to your body’s tissues, it travels into tiny vessels called capillaries. The pressure that is present within your arterial side of your capillaries is stronger than the tissues around it and this allows plasma fluid and proteins to leak out of the capillary. It does this through gaps in the capillary wall that allow larger substances like glucose to enter the cells. A majority of this fluid is reabsorbed by the capillary vessels as they join your veins. But this means that there is still some fluid left behind hanging out in your tissues. We call this remaining fluid “lymph” and it needs a way to get out of your tissues and back into your blood stream. This is where the lymphatic vessels come into play. Your lymphatic system has it’s own vessels that also branch into small vessels called lymphatic capillaries. These intertwine alongside the capillaries carrying your blood and they serve to collect the lymph (those proteins that weren’t supposed to be out of the capillaries get swept up by the lymph also). The lymph travels along your lymphatic vessels as they get larger and larger until it reaches one of two main collecting ducts. These are located within your chest and return the lymph into one of your largest veins right before it enters the heart. This is the farthest point from where blood is pumped out of your heart which means the pressure in this vessel is low enough that the lymphatic system is able to use that to its advantage to be able to return the lymph into your bloodstream. The lymph moves through the blood vessels utilizing the pressure of your nearby blood vessels and the contraction of your muscles to carry it through a series of one way valves in the lymphatic vessels.

Role 2: Immunity

When the plasma leaks into your tissues and becomes lymph it can also serve to clean up some of the substances in the area. For example, when you cut your skin, bacteria can enter into your tissues. Your body has white blood cells all throughout it that serve to fight infection and a very large portion of them are located in what we call “lymph nodes.” When the lymph is collected up by the lymphatic capillaries it serves an important role of helping to carry that infection to the lymph nodes where it can be attacked by specialized white blood cells known as B and T cells. This is very important because as we just learned all vessels of the lymphatic system lead directly to the bloodstream. We do not want any bacteria or infection to reach the blood stream. This means that our lymph nodes have an extremely important job of dealing with any bacteria or virus that enters the lymphatic vessels before it can reach the blood stream. This is where we see a large amount of overlap between the immune system and the lymphatic system. There are several types of white blood cells, one of them being lymphocytes. Your lymphocytes are identified as being either “B cells” or “T cells.” Simply put, B cells make antibodies, while T cells destroy infected cells. Any foreign substance that enters the body is considered an antigen (think virus, bacteria or even your own cells that become cancerous). Your immune system has the amazing ability to learn. It does this by creating antibodies in it’s B cells. Once it has fought off a foreign substance, antibodies against that substance will continue to circulate throughout your body, ready to recognize and attack if that same foreign antigen ever enters your body again. They are found everywhere from your bloodstream to your lungs, mucus, saliva and breast milk. Lymphocytes play a major role in your lymphatic system as we see in the image below.

Role 3: Fat Transport

When fat gets absorbed into the tissues of your small intestine it is too large to get absorbed into your bloodstream like other particles such as glucose are. In order for fat to be able to enter your blood your body uses a part of the lymphatic system called a lacteal. A lacteal is similar to a lymphatic capillary in that it picks up the fat so that it can be carried through the lymphatic vessels until it reaches the lymphatic ducts that will allow it to enter the bloodstream. You begin to realize the importance of this when you consider that this is the way that fat-soluble vitamins (think vitamin A, D, E and K) get absorbed into your bloodstream, after digestion they travel through the lymphatic system to enter your bloodstream.

Phew! What an amazing system, am I right? The design of the body is absolutely incredible and how it all interconnects. The other systems that overlap closely with the lymphatic system are the Gastrointestinal System, the Immune System, and the Vascular System. Next we will discuss how your body is effected when your lymphatic system stops functioning correctly.