HB-087 · Lymphatic & Immune · Part
Thymus
Also called: thymus Thymus
3D anatomy data Classes 9-10 · Classes 11-12 Intermediate Draft - educator review
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Parts: capsule; lobules; cortex; medulla
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About
The thymus trains T lymphocytes; it is large in children and shrinks after puberty.
- 📍 Where it is
- Upper chest behind the sternum, in front of the heart and great vessels.
- 🧱 Structure
- Two lobes with an outer cortex and inner medulla full of developing T cells.
- ⚙️ What it does
- Maturation and selection of T cells for the immune system.
💡 Key facts
- "T" cells are named after the thymus.
- It is biggest relative to body size in early childhood.
- In adults it is largely replaced by fat.
✗ The thymus is useless in adults
✓ It did its main job early, building the T-cell army that lasts for years.
📒 Words to know
- T cell
- lymphocyte trained in the thymus
- lymphocyte
- type of white blood cell
- involution
- shrinking with age
🏫 Related lessons
- Cells and microorganisms Classes 6-8
- Health education Classes 9-10
Generic GayaGnan topic lessons. Check your own board's syllabus for the exact chapter.
🔎 Sources and credits
Catalog description: Lobulated immune organ.
- OpenStax Anatomy and Physiology 2e, ch. 21 (lymphatic and immune system) (accessed 2026-10-30)
- 3D models: BodyParts3D (DBCLS) and the Human Reference Atlas (HuBMAP), CC BY 4.0, with GayaGnan schematics. 3D model credits
For learning only. This site does not give medical advice, diagnosis or treatment, and it does not collect any health data.