The Thymus is an obscure organ located deep within the chest. It may not function throughout human life but is a very important organ while active. Read on to explore more about thymus.

What is Thymus?

The thymus gland is a very unique organ that is at its largest in children and shrinks away as the body grows older. It is about 2.5 to 5 cms wide, 4 to 6 cms long and 1 cm thick at birth. At its largest instance, (viz. during puberty) the thymus weighs just under 30 grams. After puberty, the thymus slowly starts to shrink and by the age of 75, it is nothing more than fatty tissue.

Thymus Location

The thymus gland is located in the anterior part of the chest, right behind the breastbone (or the sternum) and between the lungs. It has a pinkish-grey complexion and is lobed, with primary two lobes and smaller lobes radiating from within. The two lobes may be separated or united and generally vary in size.

Histology of Thymus

There are two general cell lines of interest in the thymus. These are thymic epithelial cells and lymphoid cells. The lymphoid cells migrate into the thymus during the intrauterine angiogenesis. The thymic epithelium is important for the maturation and development of these lymphoid cells.

The lymphoid progenitor cells can access the thymus in the 10th week of gestation. A well-differentiated thymus is observed in the 12th week of gestation.

Thymus Function

One of the most important functions of the thymus is to stimulate the production of very specialized cells called T-cells (also called T-lymphocytes). These cells are responsible for directly fending off foreign pathogens such as viruses and bacteria. They also regulate the immune system, helping to prevent autoimmunity, wherein, the body’s immune system elicits immune responses on its own healthy cells.

Thymus also secretes thymosin to stimulate the development of T-cells.

Thymus Gland Disorders

The most common disorders caused by the dysfunctioning of thymus gland are- Myasthenia gravis, pure red cell aplasia, and hypogammaglobulinemia.

Myasthenia gravis is caused due to abnormal enlargement of the thymus. The enlarged thymus produces antibodies that destroy the muscle receptor sites. Thus the muscles become very weak.

Pure red aplasia is caused when the patient’s own immune cells attack the blood-forming stem cells. This happens when there is a tumour in the thymus.

Hypogammaglobulinemia occurs when the body does not produce enough antibodies.

Thymosin- The Thymus Hormone

To stimulate the production of T-Cells, the thymus secretes a hormone called Thymosin. Then, a type of white blood cell called lymphocytes pass through the thymus and gets transformed into T-Cells. Once these T-cells have matured, they migrate to the lymph nodes in the body and consequently aid the immune system. The thymus gland is only active until puberty, however, they produce all the T-cells required by the body well before this period.

Facts About Thymus

  • The thymus gland is located behind the sternum and between the lungs.
  • This gland is only active until puberty.
  • Thymus starts to shrink after puberty and is replaced with fat.
  • Thymus produces thymosin that triggers the development of T-cells.
  • Thymus cancer is a disease associated with thymus. The cancer is malignant in about 35% of the cases and can be treated through surgery, or chemotherapy.

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Further Reading

Endocrine System: Ductless Glands
Immune System – Active and passive immunity

Frequently Asked Questions


Where is the thymus gland located?

Thymus is located in the upper part of the chest, between the lungs. It is slightly large in infants and shrinks as the child grows. In adults, it shrinks even more and is replaced with fat.


Name the hormone produced by the thymus.

Thymosin hormone is produced by thymus. This hormone stimulates the development of T-cells. The white cells pass through the thymus throughout childhood and are transformed into T-cells. The matured T-cells travel to the lymph nodes, where they help the immune system in fighting diseases.


What is the function of the thymus?

Thymus produces progenitor cells that develop into T-cells. These T-cells help the body fight against infections. They also aid in the growth of other organs in the immune system.


What are T-Cells?

T-cells are a type of white blood cell that originates in the bone marrow and mature in the thymus. They play an important role in defending the body against viruses, protozoa and bacteria.


Write a short note on the Thymus.

Thymus is an irregular-shaped gland located in the upper part of the chest, between the lungs. It is large during childhood and shrinks as the body grows. It is a part of the lymphatic system along with the spleen, tonsils and adenoids. It also forms a part of the endocrine system. It is made up of epithelial cells, lymphocytes and fat tissues. This gland is active only until puberty.


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