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What Organs Are Part of the Lymphatic System?

The lymphatic system includes a system of lymphatic capillaries, vessels, nodes, and ducts that collects and transports lymph, which is a clear to slightly yellowish fluid, similar to the plasma in blood. The lymphatic system is important for maintaining your body’s fluid balance, and it helps transport some fats. It also works along with the rest of the immune system (namely, the leukocytes) to fight infections.

In addition to being present in the lymph nodes, lymphatic tissue is also found in a few additional spaces of your body. The lymphoid organs assist the lymphatic system. They include the thymus, spleen, tonsils, and appendix, along with some special tissue in the gut:

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  • The thymus: The thymus is located in the thoracic cavity, just under the neck. It’s made up of two lobes of lymphoid tissue. Each lobe has a medulla surrounded by a cortex. The cortex is where immature lymphocytes first go to become T cells, but their maturation finishes in the medulla.

    The thymus is large during childhood, but during the early teen years it starts to decrease in size. Why does it get smaller (or to be more clinical, involute)? No one knows — it’s still a mystery.

  • The spleen: The spleen is located in the upper-left part of the abdomen. It’s tucked up under the ribs, so you generally can’t palpate it (medically examine by touch) unless it’s enlarged.

    The spleen’s main function is to filter the blood. It removes old or damaged red blood cells, which are phagocytized by macrophages. The spleen also detects viruses and bacteria and triggers the release of lymphocytes.

  • The tonsils: The tonsils are masses of lymphoid tissue found in the back of the throat and nasal cavity. They’re part of the immune system, so they help fight infections, but removing the tonsils doesn’t appear to increase your risk of infections.

    Tonsillitis occurs when the tonsils become infected. They’re usually easy to see by shining a light into your patient’s mouth. Infected tonsils are usually red and swollen, or they may have a whitish coating on them. Sometimes tonsils are enlarged but not actually infected.

  • The appendix: The appendix is a pouch of lymphatic tissue that’s attached to the large intestine. It’s located in the lower-right area of the abdomen. Although it’s made of lymphatic tissue, the appendix doesn’t appear to have much lymphatic function in humans, but it does release some mucus into the large intestine.

    An obstructed appendiceal lumen (opening) can cause appendicitis when bacteria start to multiply. The result is abdominal pain and tenderness over the appendix.

Some lymphatic tissue similar to the tonsils is also located in the digestive tract. Called gut associated lymphoid tissue (GALT), it comes in the following three varieties:

  • Peyer’s patches: These patches of lymphoid tissue are located in the mucosa and submucosa throughout the small intestine, although they’re more concentrated in the ileum. Peyer’s patches contain mostly B cells.

  • Lamina propria lymphocytes: This type of GALT is located in the mucosa of the small intestine. It also contains mostly B cells.

  • Intraepithelial lymphocytes: These tissues are located between the cells of the epithelial layer of the small intestine, between the tight junctions.

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