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The Human Body and the Anatomy of the Immune System

The immune system consists of different parts of the human body that work together to identify and stamp out viruses, bacteria, and diseases. This body system encompasses the bone marrow, thymus, lymph nodes, spleen, and lymphoid tissue.

Bone Marrow

Bone marrow, a substance that's found inside of your bones, makes blood cells, including the white blood cells and platelets that your body uses to respond to illnesses and injuries. The pelvis contains the most bone marrow, but it's also found in the center of other bones.


The thymus is a gland that makes T cells, a specific type of white blood cell, and trains these cells to fight infections. It's located behind your sternum, between your lungs and just above your heart.

Lymph Nodes

Lymph nodes are responsible for filtering waste from your lymph fluid, including foreign matter like cancer cells, harmful bacteria, and invasive fungi like candida. Hundreds of lymph nodes are located all over the body, but they're most noticeable in your neck, armpits, and groin.

  • The Role of Lymph Nodes in Cancer Treatment: The lymph nodes will naturally try to filter out cancer cells, so people with cancer often have it in their lymph nodes.
  • Swollen Lymph Nodes: Infections can cause your lymph nodes to swell, up, a condition called lymphadenopathy. Once the infection is gone, the lymph nodes should return to their normal size.
  • Lymphadenopathy in Children: Swollen lymph nodes, sometimes called "swollen glands," are common in children because they can accompany common infections like strep throat or the flu.
  • Lymphadenectomy: If cancer is suspected in a lymph node, it may need to be surgically removed and examined.
  • Lymphedema: Lymphedema is swelling that's caused by a buildup of lymphatic fluid.


The spleen is an organ that filters and stores blood. It's made of red pulp, which removes damaged blood cells, and white pulp, which makes white blood cells.

  • What Does the Spleen Do? Inside the spleen, damaged blood cells are filtered out and broken down.
  • Splenic Sequestration Crisis: When someone has sickle cell anemia, these malformed cells can clog up the spleen, trapping blood inside and causing the spleen to enlarge.
  • How the Spleen Filters Blood: Research has found that a slit inside the spleen acts as a filter that keeps misshapen blood cells from passing through.
  • Splenic Conditions: If you have an infected or ruptured spleen, prompt medical treatment is essential.
  • Enlarged Spleen (Splenomegaly): Many conditions can cause an enlarged spleen, from a viral infection to cancer or lupus.

Mucosa-Associated Lymphoid Tissue (MALT)

Mucosa-associated lymphoid tissue, or MALT, is located throughout the body in the mucosal linings of organs and body cavities. Mucosal tissues are good places for pathogens to enter the body, and when this happens, MALT begins the body's immune response.

Lymphocyte Recirculation

Lymphocytes are the white blood cells that help your body to fight infection, and they travel throughout the body between the lymphatic and circulatory systems in a process called lymphocyte recirculation.

Additional Reading on the Immune System and Human Body

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