What is the Thymus?


The thymus is an essential organ located directly behind the sternum and in between the lungs. Its main function is to foster the development of T-cells during childhood and puberty.

Before a child is born, the thymus is essential to an individual’s health, promoting a healthy immune system by creating T-cells which play an important role in the lymphatic and endocrine system. T-cells are an important piece of the body’s immune system as they help avoid bacterial and viral infections.

The thymus is divided into 3 main layers:

  • The capsule covers the outside of the thymus
  • The cortex surrounds the innermost section of the thymus
  • The medulla is the center of the organ

Since it is inactive after puberty, the thymus is at its largest during childhood (1oz.) and shrinks in size after puberty until it disappears. It will eventually be completely replaced by fat.

Thymosin is the hormone released by the thymus that stimulates the development of T-cells. White blood cells will enter the thymus throughout childhood and be transformed into T-cells. Once a T-cell has fully matured, it will move to a lymph node, attacking pathogens in the body. However, thymus cells can develop into cancerous cells.

The thymus contains 3 types of cells, which can develop into different forms of cancer:

Epithelial cells serve as the foundation for the thymus, providing its structure. Thymic carcinomas and thymomas develop from this type of cell.

Lymphocytes are the second part of the thymus, and can develop into the more well-known cancers, Hodgkin's lymphoma and non-Hodgkin's lymphoma.

The last type of cells are Kulchitsky cells, also known as neuroendocrine cells. These cells make up a small part of the thymus and are used to release hormones such as thymosin. These cells can develop carcinoid tumors.

Photo by Sanja Gjenero

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