Dermatology: Anatomy & Structure of Hair
Hair is a specialized keratinized appendage of the skin. Understanding its structure is essential for diagnosing alopecias and hair shaft disorders.
Microscopic Structure (Inside-Out)
| Layer | Description |
|---|---|
| Medulla | The innermost core is often absent in thin (vellus) hair. Contains soft keratin. |
| Cortex | The bulk of the hair shaft contains melanin (pigment) and hard keratin. Determines hair strength and color. |
| Cuticle | The outermost layer is composed of overlapping, transparent cells (shingle-like) that protect the cortex. |
The Hair Follicle (The “Root”)
- Bulb: The expanded base containing the hair matrix (rapidly dividing cells) and melanocytes.
- Dermal Papilla: Invagination at the base of the bulb; vascularized connective tissue that supplies nutrients to the matrix.
- Hair Cycle:
- Anagen: Growth phase (lasts 2–7 years).
- Catagen: Regression phase (2–3 weeks).
- Telogen: Resting phase (2–3 months).
High-Yield Exam Pearl:
- Telogen Effluvium: A common post-stress/post-partum condition where a large percentage of follicles shift prematurely from Anagen to Telogen, leading to diffuse shedding.
- Anagen Effluvium: Seen in chemotherapy; results from sudden toxic damage to the rapidly dividing matrix cells in the Anagen phase.