The thymus is a small, lymphoid organ located in the upper anterior portion of the chest cavity, just behind the sternum.
It plays a vital role in the development and maturation of T-lymphocytes (T cells), which are crucial components of the adaptive immune system.
The thymus is most active during childhood and adolescence, gradually decreasing in size and function with age, a process known as involution.
Structure of Thymus
1. Location and Appearance:
The thymus sits in the mediastinum, the central compartment of the thoracic cavity.
It is larger in infants and children and tends to shrink after puberty.
2. Composition:
The thymus is divided into two main sections called lobes, which are surrounded by a capsule.
Each lobe is further divided into numerous lobules, which contain an outer cortex and an inner medulla.
3. Cortex and Medulla:
The cortex is densely packed with immature T cells, while the medulla contains more mature T cells.
The organ's structure facilitates the development and selection of T cells that can effectively respond to pathogens without attacking the body's own tissues.
Function of Thymus
1. T Cell Maturation:
The primary function of the thymus is to produce and mature T cells.
Immature T cells (thymocytes) originate from bone marrow and migrate to the thymus, where they undergo a process of maturation and selection.
2. Central Tolerance:
The thymus plays a crucial role in developing central tolerance, the mechanism by which T cells that are reactive to self-antigens are eliminated, preventing autoimmune diseases.
3. Secretion of Thymic Hormones:
The thymus secretes hormones such as thymosin, thymopoietin, and thymulin, which are involved in T cell development and differentiation.
Disorders of Thymus
Thymus disorders affect the immune system by impairing T cell production and function:
1. Thymoma and Thymic Carcinoma:
Tumors from thymic epithelial cells; thymomas are typically benign, while thymic carcinomas are more aggressive.
Symptoms may include cough, chest pain, and difficulty breathing, though thymomas are often asymptomatic.
2. Myasthenia Gravis:
An autoimmune disorder linked to thymic abnormalities, often thymoma.
It causes muscle weakness due to antibodies attacking muscle receptor cells.
3. DiGeorge Syndrome (22q11.2 Deletion Syndrome):
A genetic disorder affecting thymus development, leading to reduced T cell production and increased infection risk.
4. Immunodeficiency Disorders:
Conditions like complete DiGeorge Syndrome, where the thymus is absent, result in severe T cell deficiency.
Treatment of Thymus
1.Thymomas and Thymic Carcinomas:
Surgical removal is the primary treatment, sometimes followed by radiation or chemotherapy.
2.Myasthenia Gravis:
Treated with medications, immunosuppressants, and sometimes thymectomy (removal of the thymus).
3.DiGeorge Syndrome:
Managed with symptom management, thymus transplantation in severe cases, and calcium supplements.