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M01.05.010 Thymus Gland
The thymus gland is a vital lymphoid organ located in the thoracic cavity and neck. Its role in the development of the immune system is crucial during adolescence, after which it gradually involutes and is replaced by fat. This article explores the embryological origin, anatomical structure, position, vasculature, and clinical relevance of the thymus gland.
Embryological Origin
- Derived from: The third pharyngeal pouch during embryological development.
Anatomy of the Thymus Gland
Structure and Position
- Shape: Asymmetrical, flat, and lobular.
- Lobular Components:
- Cortical Portion:
- Located peripherally in each follicle.
- Composed mainly of lymphocytes supported by epithelial reticular cells.
- Medullary Portion:
- Found centrally in each follicle.
- Contains fewer lymphocytes and a higher number of epithelial cells.
- Hassall’s Corpuscles: Concentric arrangements of epithelial reticular cells; their function remains unclear.
- Cortical Portion:
Position
- Thoracic Location: Primarily in the superior mediastinum, posterior to the manubrium of the sternum.
- Extensions:
- Superiorly: Into the neck, reaching the thyroid gland in some individuals.
- Inferiorly: Into the anterior mediastinum, in front of the fibrous pericardium.
Vasculature
- Arterial Supply:
- Anterior intercostal arteries.
- Branches from the internal thoracic arteries.
- Venous Drainage:
- Left brachiocephalic vein.
- Internal thoracic veins.
Clinical Relevance
DiGeorge Syndrome
- Cause: Deletion of a segment of chromosome 22.
- Mnemonic for Key Features: “CATCH”
- Congenital heart defects.
- Abnormal facies.
- Thymic aplasia.
- Cleft palate.
- Hypoparathyroidism.
- Immune Deficiency: Individuals with thymic aplasia are prone to recurrent infections due to an underdeveloped immune system.
Summary Table: Key Points of the Thymus Gland
| Feature | Details |
|---|---|
| Embryological Origin | Third pharyngeal pouch. |
| Structure | Lobulated with cortical and Medullary components. |
| Location | Superior mediastinum; can extend into the neck or anterior mediastinum. |
| Vascular Supply | Anterior intercostal arteries, internal thoracic arteries, brachiocephalic veins. |
| Clinical Relevance | DiGeorge syndrome: thymic aplasia causing immune deficiencies. |
Points to Remember
- The thymus gland is essential for immune system development in adolescence.
- Its unique structure includes cortical and Medullary portions with Hassall’s corpuscles.
- Post-puberty, it undergoes involution and is replaced by fat.
- DiGeorge syndrome highlights its clinical significance due to immune implications from thymic aplasia.
Bibliography
- Refer to textbooks like Gray’s Anatomy and Robbins Basic Pathology for in-depth understanding.
- Online resources like PubMed and medical school portals for updated research.