Thymus

• 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 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:

   • It 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, where they undergo a process of maturation and selection.

2. Central Tolerance:

   • It 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 secretes hormones such as thymosin, thymopoietin, and thymulin, which are involved in T cell development and differentiation.

Disorders of Thymus

• It 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.

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