What is the lymphatic system? I can imagine most people don’t know what it does—and it’s probably one of the most understated systems of the body. It often gets lumped in with the immune system and circulatory system, since they are so tightly connected. In fact, sometimes it’s hard to tell where the those systems end and the lymphatic system begins, so yeah, I get it.
Technically speaking, the lymphatic system is comprised of the lymphatic organs and lymphoid tissues.
LYMPHATICS – Green labels in the diagram below.
The lymphatics begin with the lymphatic capillaries, permeable endothelial vessels one-cell thick, which absorb all the fluid, particles, microbes, and debris from your tissues, and from the small intestines, fat. Lymphatic capillaries empty into larger lymph vessels that eventually empty their contents—a fluid called ‘lymph’—into the veins through lymphatic ducts.
Think ‘garbage collector’.
But here’s the cool part: The lymphoid tissues then go through the garbage to see what’s up—is there stuff that shouldn’t be in there? And if there is, then it adds stuff to the lymph to help the body fight off foreign invaders.
LYMPHOID TISSUES – Blue labels in the diagram below
The main lymphoid tissue that you might be familiar with is the lymph node.
Lymph nodes are interposed between lymph vessels at some of the junctions between vessels. There’s a TON of these guys – check out the graphic below. That fluid we talked about, lymph, is modified as it stops by each lymph node: debris is filtered out, immune cells called lymphocytes are activated, and antibodies and lymphocytes are added to the fluid to help fight off whatever infection or foreign invaders may be lurking around.
Other lymphoid tissues have similar functions:
- The spleen filters the circulating blood, to which it adds antibodies and lymphocytes.
- Tonsils, Peyer patches, and other unencapsulated lymphoid tissues line epithelia that are in contact with the outside environment.
- Unencapsulated lymphoid tissues activate lymphocytes and manufacture antibodies against foreign antigens.
- Lymphoid tissues in the bone marrow are proliferation and activation centers for lymphocytes
- The thymus is a proliferation and maturation center for T lymphocytes, esp. during the neonatal and early postnatal years.
