The thymus gland is a specialized organ within the human body that often goes unnoticed, despite its significant role. Its functions are distinct and contribute to the body’s defense mechanisms.
What the Thymus Is and Where It’s Located
The thymus gland resides in the upper chest, behind the breastbone (sternum) and nestled between the lungs. This organ is part of the lymphatic system, a network of tissues and organs that help the body fight disease. It is classified as a primary lymphoid organ, indicating its role in the development of immune cells. The thymus is composed of two irregularly shaped lobes, which feature numerous small bumps on their surface, referred to as lobules.
How the Thymus Supports Your Immune System
The thymus gland’s primary function involves the maturation of T cells, also known as T lymphocytes. T cells, a type of white blood cell, originate in the bone marrow and travel to the thymus for their final stages of development. Within the thymus, immature T cells multiply and differentiate into specialized types, including helper, regulatory, cytotoxic, and memory T cells. Once mature, these T cells are released into the bloodstream and lymphatic system, ready to identify and neutralize foreign invaders.
The thymus also produces several hormones that regulate T cell production and maturation. These include thymosin, thymopoietin, and thymulin. Thymosin ensures that T cells undergo complete maturation after they leave the thymus, enabling them to effectively combat pathogens. Thymopoietin and thymulin contribute to T cell development. These hormones collectively help to enhance the immune system’s ability to respond to potential threats.
The Thymus Across the Lifespan
The thymus gland changes throughout a person’s life, being most active during childhood. It begins producing T cells before birth and continues production throughout childhood and adolescence. During this period, particularly before puberty, the thymus reaches its largest size, weighing approximately 25 grams at birth and peaking at around 35 grams between 12 and 19 years of age. This early activity ensures the body produces most of the T cells it will need for a lifetime of immune defense.
Following puberty, the thymus undergoes a process called thymic involution, where it gradually shrinks and is replaced by fatty tissue. By age 60, its weight may decrease to about 15 grams, and by age 75, it can be largely composed of fatty tissue. Despite this reduction in size and activity, adults can live without a fully active thymus because most T cells were produced and matured during younger years. However, if the thymus is removed in infants or young children, it can lead to severe immunodeficiency, as their immune system has not yet established a sufficient reserve of mature T cells.
Common Conditions of the Thymus Gland
Several conditions can affect the thymus gland, impacting its function and the immune system. One such condition is thymic hyperplasia, an increase in the size of the thymus due to cell overgrowth. While often a benign enlargement, it can sometimes be associated with autoimmune disorders.
More serious conditions include cancers of the thymus, primarily thymoma and thymic carcinoma. Thymoma is a slow-growing tumor originating from the thymus’s epithelial cells, often associated with autoimmune conditions like myasthenia gravis. Thymic carcinoma is a more aggressive cancer that can spread. Both types of cancer can cause symptoms like shortness of breath, chest pain, and a persistent cough, often due to the tumor pressing on surrounding organs. Additionally, severe atrophy, distinct from age-related involution, can affect the thymus, leading to impaired immune function.