Thymus

The thymus performs several critical functions for immune health:

• T-Cell Maturation: Educates and differentiates immature T-cells for immune defense
• Immune Tolerance: Helps prevent autoimmunity by eliminating self-reactive T-cells
• Hormonal Secretion: Produces thymosins, thymopoietin, and thymulin to regulate T-cell activity
• Immune System Support: Provides early-life programming of adaptive immunity
• Lymphoid Organ Development: Interacts with bone marrow and lymph nodes to establish immune networks

Key Takeaway

The thymus is a central organ for developing a competent and self-tolerant immune system, ensuring that T-cells can defend the body against pathogens without attacking its own tissues.

Basic Structure

• Soft, bilobed organ
• Located in the superior mediastinum, anterior to the heart and behind the sternum
• Composed of an outer cortex and inner medulla
• Surrounded by connective tissue capsule with septa dividing lobules

Major Regions

• Cortex: Dense region where immature T-cells proliferate
• Medulla: Contains mature T-cells and thymic epithelial cells
• Hassall’s Corpuscles: Specialized structures in the medulla involved in T-cell education

Nerves & Blood Supply

• Blood Supply: Branches of the internal thoracic and inferior thyroid arteries
• Venous Drainage: Internal thoracic and brachiocephalic veins
• Innervation: Sympathetic fibers from the thoracic sympathetic trunk

Key Takeaway

The thymus’ structure—cortex, medulla, and specialized epithelial cells—enables the education, maturation, and selection of T-cells, forming the foundation of adaptive immunity.

• The thymus is largest and most active during childhood and adolescence
• In adults, the thymus gradually involutes and is replaced by adipose tissue
• T-cell production continues into adulthood despite thymic involution
• Hassall’s corpuscles play a role in inducing tolerance to self-antigens
• The thymus was historically mistaken for a lymph node due to its location and lymphoid tissue

• DiGeorge Syndrome: Congenital absence or hypoplasia of the thymus causing immune deficiency
• Thymoma: Tumor of thymic epithelial cells, may be associated with myasthenia gravis
• Severe Combined Immunodeficiency (SCID): T-cell development failure affecting immunity
• Thymic Hyperplasia: Enlargement, often associated with autoimmune conditions
• Autoimmune Diseases: Result from impaired thymic selection of self-reactive T-cells

• Frequent infections or prolonged illness
• Delayed immune response to vaccines or pathogens
• Autoimmune symptoms (e.g., chronic inflammation, joint pain)
• Fatigue and poor recovery from illness
• Lymphatic swelling or recurrent throat infections

Source: Sam Webster