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Immune System: Anatomy and Physiology Part 2

Updated: Mar 14, 2020

Immune System: Anatomy and Physiology Part 2

Our bodies’ immune defense is very complex, and technically interrelates with many systems throughout the body. However, we will focus on several organs and cells that are distinctly categorized a the “immune system.”

I will systematically paint each part and its function to expand the picture of this amazing system.

Bone Marrow

Location: Found in flat bones and in the end of long bones in adults.

Function: Bone marrow produces red blood cells (which carry oxygen to cells), platelets (that stop bleeding through blood clotting) and white blood cells (which fight infection). Our white blood cells include the neutrophils and macrophages of our “Non-Specific Internal ‘Innate’ Immunity” and the lymphocytes that divide into T and B cells of the “Adaptive Immunity.” (These lines of defense with their specific cells were discussed in last week’s article.)


Location: A small 2-4” pouch located where the small and large intestine meet.

Function: While this organ has long been considered dispensable, studies are now revealing that the appendix plays a very supportive role in the immune system by housing good bacteria. In the event that the contents of the colon are purged (diarrhea), the bacteria residing in the appendix are ready to re-inoculate the colon. [1]

Lymphatic Nodules (Lymph Nodes)

While many lymph nodes are solitary throughout the body, others occur as large clusters in a specific region. The tonsils and peyer’s patches are among these clusters.

Peyer’s Patches

Location: Lymphatic follicles located in the small intestine.

Function: This cluster provides a major site of surveillance of pathogens. This is where our adaptive immune system comes alive by detecting invaders, destroying them, and then creating antigens to them.


Location: Small organs in the back of the throat, oral cavity, and nasal cavity. They are divided into five sections: adenoids, embedded in the throat; two palatine tonsils at the back of the mouth (commonly removed in tonsillectomy); and the paired lingual tonsil, at the base of the tongue.

Function: Although easily devalued, the tonsils play a vital role within the immune system. Their various immune cells, white blood cells, destroy pathogens that enter the nose and mouth before they spread to the rest of the body.


Location: A gland lies behind the breast bone and above the heart.

Function: It supports the immune system by “training up” T-cells. Immature T-cells migrate from red bone marrow to the thymus to begin their education. Only about 2% of these cells will graduate and be sent via the blood to populate lymphatic tissue to fight infection and destroy bacteria. The other 98% die off and are cleared by the thymic macrophages.


Location: A large mass of lymphatic tissue located between the stomach and diaphragm.

Function: In the unborn child, this organ produces blood and defense cells. After birth, the spleen functions to filter and recycle red blood cells. It also stores platelets and white blood cells.

While our bodies can incredibly adapt when one organ is weak (or removed), it was designed for every organ and cell to thrive synergistically. Together, they craft a masterpiece for a strong and effective immune system!


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