Thymus Anatomy
Developmental Origin
- Embryology: Derived from the third pharyngeal pouch (endodermal origin).
- Descent: Descends into the anterior mediastinum.
Microscopic Organization
| Region | Function/Feature |
|---|---|
| Cortex | Site of Positive Selection; immature thymocytes (dense). |
| Medulla | Site of Negative Selection; contains Hassall corpuscles. |
NEET PG “Must-Know” Pearls
- DiGeorge Syndrome: Failure of 3rd and 4th pharyngeal pouch development; leads to thymic hypoplasia/aplasia and T-cell deficiency.
- Hassall Corpuscles: Concentric lamellated epithelial reticular cells found in the medulla; a hallmark histological feature.
- Involution: Undergoes fatty replacement (involution) after puberty; rarely fully disappears.