Thymus gland definition structure and function with diagram
The thymus, a primary lymphoid organ, is a key component of our immune system. It functions as the site of T cell maturation and development. It is active only till puberty and starts to slowly shrink and get replaced by fat. Though it is little-known and not active post-puberty, yet, it plays a very vital role in protecting us against autoimmune disorders. Autoimmunity is the condition which occurs when our immune system goes rogue and starts destroying itself.
The following section will shed light on thymus and thymus function.
Thymus Gland Location
The thymus is a soft, bilobed structure and is encased between the chest, the breastbone or sternum and between the lungs. To be precise, the thymus lies encapsulated in the superior mediastinum and the anterior region of the inferior mediastinum, next to the pericardium of the heart. Also, this is almost anterior to the heart vessels, and somewhat deep inside the sternum.
The phrenic nerves, which connect and supply to the diaphragm, lie parallel to the left and right side of the thymus. The two different lobes of the thymus are connected in the middle with the help of the isthmus.
While the thymus is functional in infants, it is redundant in adult humans. As a child slowly approaches puberty, the thymus starts to shrink and eventually, replaced by fat. Surprisingly, in adults, the thymus weighs only about 5 grams.
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Read on to find out more about thymus function.
Thymus Gland Function
As mentioned above, the thymus is the site of development of progenitor cells, which are the precursors of mature T-cells (cells derived from the thymus). Our body employs these T-cells to help locate and destroy cells that are infected, cancerous or prone to disease. These mature T-cells also provide a safe space to other organs of the immune system to gain nourishment and grow.
Furthermore, the T-cells help fend off foreign disease-causing pathogens such as deadly viruses and bacteria. Thus, the thymus helps to regulate the immune system and prevent autoimmunity in the body.
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Rack Your Brains: Now that you know how the thymus works, it’s time to find out how to test thymus function. Consult your teacher, mentor or a school senior and conduct experiments to know how it works.
Pop Quiz 1
Which of these are cells produced by the thymus?
A-cells
B-cells
C-cells
T-cells
Thymus Gland Hormones
The thymus releases a hormone called thymosin which helps kickstart the production of T-cells. Throughout childhood, lymphocytes, a type of white blood cells are known to pass through the thymus, wherein they are ultimately changed into T-cells.
As T-cells attain maturity, they move towards the lymph nodes, which are clusters of immune cells distributed all over the body. However, regardless of where they are located, these T-cells can sometimes develop into cancerous tumours, and the condition is known as Hodgkin disease. These cells are called non-Hodgkin lymphomas.
Thus the most significant thymus function is its role in protecting the body from all sorts of diseases and ensuring its long-term health. The dysfunction of the gland can cause major diseases, for instance, red cell aplasia, myasthenia gravis and hypogammaglobulinemia.
This was all about thymus definition and function. For more on the endocrine system and its various glands, sign up for live demo classes and watch them for free on our Vedantu app.
FAQs on Thymus Gland and Its Role in Human Immunity
1. What is the thymus and where is it located?
The thymus is a primary lymphoid organ located in the upper chest, behind the sternum and in front of the heart. It is part of the immune system and plays a key role in T cell development.
- Located in the anterior mediastinum
- Most active during childhood
- Shrinks after puberty in a process called thymic involution
2. What is the function of the thymus gland?
The main function of the thymus gland is to mature and differentiate T lymphocytes (T cells). These cells are critical for adaptive immunity.
- Produces immature T cells from bone marrow precursors
- Facilitates positive and negative selection
- Ensures self-tolerance to prevent autoimmunity
3. How does the thymus help in T cell maturation?
The thymus helps in T cell maturation by exposing immature T cells to self-antigens and selecting only functional, non-self-reactive cells.
- Positive selection: T cells that recognize self-MHC molecules survive.
- Negative selection: T cells that strongly bind self-antigens are eliminated.
- Surviving cells differentiate into helper T cells (CD4+) or cytotoxic T cells (CD8+).
4. What hormones are produced by the thymus?
The thymus produces hormones such as thymosin, thymopoietin, and thymulin that regulate T cell development. These hormones support immune cell differentiation.
- Stimulate maturation of T lymphocytes
- Enhance immune system regulation
- Promote development of immune competence
5. Why does the thymus shrink after puberty?
The thymus shrinks after puberty due to a natural process called thymic involution, influenced by sex hormones. Its active tissue is gradually replaced by fat.
- Peak size and activity occur in childhood
- Shrinkage begins during adolescence
- Some T cell production continues in adulthood
6. What is the structure of the thymus?
The thymus is a bilobed organ divided into an outer cortex and an inner medulla. Each region plays a role in T cell development.
- Cortex: Contains densely packed immature T cells (thymocytes)
- Medulla: Contains mature T cells and Hassall’s corpuscles
- Surrounded by a connective tissue capsule
7. What are Hassall’s corpuscles in the thymus?
Hassall’s corpuscles are concentric clusters of epithelial cells found in the medulla of the thymus. They are involved in T cell maturation and immune regulation.
- Composed of epithelial reticular cells
- Found only in the thymic medulla
- Assist in development of regulatory T cells
8. What happens if the thymus is removed or absent?
If the thymus is absent or removed early in life, severe deficiency of T cells occurs, leading to weakened immunity. This condition impairs adaptive immune responses.
- Increased susceptibility to infections
- Reduced cell-mediated immunity
- Seen in conditions like DiGeorge syndrome
9. What is the difference between the thymus and bone marrow?
The main difference is that bone marrow produces immune cell precursors, while the thymus matures T lymphocytes. Both are primary lymphoid organs but have distinct roles.
- Bone marrow: Produces B cells and immature T cells
- Thymus: Matures and selects T cells
- Bone marrow functions throughout life, thymus activity declines after puberty
10. Is the thymus part of the endocrine system or immune system?
The thymus is primarily part of the immune system but also has endocrine functions. It acts as both a lymphoid organ and a hormone-secreting gland.
- Immune role: Maturation of T lymphocytes
- Endocrine role: Secretion of thymic hormones
- Bridges immune and hormonal regulation
