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The lymphoid tissue consists of mesh-like areas of connective tissues within the body containing white blood cells, most commonly lymphocytes. This tissue and lymphatic vessels, which transport clear body fluid called lymph to the heart, comprise the lymphatic system. Primarily involved with immune function, the components of the lymphoid tissue include the lymph nodes, the tonsils and adenoids, the spleen, and the mucosa-associated lymphoid tissues (MALT). In addition, the thymus gland and the bone marrow play a role in lymphoid function in the body. This tissue operates to defend the body from infections, foreign materials, and spreading cancer cells.
Three broad divisions of lymphoid tissues exist, which are organized based upon the stage of lymphocyte development that occurs within each one. The primary lymphoid organs, body sites involved with the generation of lymphocytes from progenitor stem cells, make functional white blood cells that are ready to respond but not targeted to respond to a particular foreign material or cell. Secondary lymphoid organs, such as the lymph nodes, keep these "naïve" lymphocytes, and, when exposed to an invading cell, activate the lymphocytes for action against that threat. Once the body activates a lymphocyte to respond to a given threat, other lymphocytes are recruited and similarly activated so that the body can mount an immune response. Finally, the tertiary lymphoid tissue imports activated lymphocytes from the blood and lymph in cases of active body inflammation.
Excess fluid in an organ drains as lymph through lymphatic vessels to a lymph node. Lymph nodes act as filters to screen harmful materials and cells from the lymph before it eventually reenters the blood stream. The lymph nodes occur most frequently in the chest cavity, the armpit, the groin, and the neck. Composed of two layers, the lymph node percolates fluid through its outermost layer, the cortex, in which concentrated pockets of lymphocytes, called follicles, stand ready to turn on if they encounter a foreign material.
The mucosa-associated lymphoid tissue (MALT) is a widespread network of tiny clumps of lymphoid tissue scattered throughout various body tissues, including the skin, lungs, eye, and digestive tract. Mucosal surfaces of the body, including the moist linings in the mouth, nose, and throat, are often the sites of entry of bacteria and viruses. The MALT contains a variety of white blood cell types capable of mounting a first line of defense against infectious agents. Lymphoma, cancer of lymphoid tissue, can form in any site of this tissue, including areas of MALT.
@Malka -- That's certainly a creative way to look at it! I think you're right, teens would love that kind of movie as an educational tool. Especially the guys -- boys always do love a good soldier tale.
The lymphocyte cells mentioned in the article are referred to as "naive", and then you said that the old "hardened survivors" of any particular germ war would be good for only fighting one type of germ. I take this to mean that lymphocytes are only good for fighting one kind of disease or germ each, and that after your body fights off a disease, the lymphocytes die.
This got me to thinking about the life spans of the body's cells. How long
do lymphocytes live? It makes sense that they would live longer than your average cell, so that their knowledge or resistance to certain germs would be remembered, which is how your immune system can build up a resistance to a certain disease type, but I'm not actually clear on how all of that works.
So do lymphocytes hang around longer than most cells to protect the body, or do they just pass on their germ knowledge and every lymphocyte your body makes after that "knows" it already?
This is actually really fascinating stuff.Everybody always talks about the blood vessels and how blood works, and nobody ever gives lymph and the lymphatic system any credit, do they?
Judging by this article, the lymphatic system is pretty much an assembly line for lymphocytes, the white blood cells responsible for defending a person's body from germ attacks. If you personify it, it comes across like a great epic warrior story!
Think about it. First there's the primary lymphoid organs, which are the "breeding ground" for new lymphocytes, then the secondary lymph organs, which are the "training ground" for lymphocytes. After they are ready for battle, your brave little white blood cells finally go to the "battleground" -- the lymph
nodes and other areas where lymphocytes make a stand against invading cells.
Some lymphocytes die valiantly in battle! Others, the hardened survivors, are so used to battling certain kinds of germs that they are good for nothing else. They head to the tertiary lymphoid tissue to die so that they do not cause inflammation -- which could be seen as harm to native population from the soldiers' continued presence.
This could be a great educational film for teens, I think!
@TheGraham - I didn't know the tonsils had anything to do with the lymphatic system, either. The only part anybody ever told me about was the lymph nodes and the lymphatic vessels that travel between them to move lymphatic fluid around -- who knew all of this fluid shifting, lymphocyte cell activation, fluid percolation and other stuff was going on?
The body really is made of a lot of liquids, isn't it? I mean, we've got blood, we've got plasma, we've got bodily fluids like urine and stomach acid and inner ear fluids, and then we've got lymph on top of it all.
Speaking of the lymphatic system again, that reminds me of your other question. I'm not sure there
is one definite largest section of lymphoid tissue. I know it's not the MALT tissue, though, since that is one of the listed secondary lymphoid tissues. The word "secondary" implies that there is a "primary" kind, but I don't see any mention of it, so I'm left wondering as well. Maybe somebody else on here can tell us.
I had no idea that the tonsils were part of the lymph system. I wonder if people who have their tonsils removed end up with a weaker immune system to show for it?
Then again, maybe all of the infection problems they have with their tonsils that lead up to the tonsil removal surgery indicate a problem with how well the tonsils are functioning and they wouldn't have helped the immune system in that condition anyway.
So, what is the largest collection of lymphoid tissue in the body? I know it's not the tonsils; they're pretty little. If I had to guess I'd say either the spleen, the lymph nodes and associated vessels since they reach throughout the
body and might add up to a good amount of mass all together.
Those, or the MALT -- mucosa-associated lymphoid tissues -- which I assume are the parts of your body that get more mucus when you get sick as a reaction on the part of your immune system. Does anybody know for sure where the most lymphoid tissue is in the body?
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