Internal Organization of a Hair Strand

Description

Seen in relation to the scalp and occipital skin, the hair (pilus) is treated as a shaft emerging from a follicular unit, then enlarged to reveal its internal organization. The outer cuticle forms overlapping keratinized scales around the cortex, while the central medulla, when present, lies on the longitudinal axis of the shaft. Proximally, the shaft transitions toward the follicle at the skin surface, and distally it continues as the free hair fiber. Cuticle, cortex, and medulla matter because many clinical and cosmetic problems localize to a specific layer, and this cutaway view makes those targets easy to teach. Bleaching, perming, and UV damage disrupt cuticle integrity and expose the cortex, increasing friction and water uptake and producing weathering signs like trichoptilosis (split ends). In dermatopathology and trichoscopy, shaft disorders such as trichorrhexis nodosa or bubble hair reflect cortical disruption, while medullary changes can help differentiate hair types and some syndromic findings. Small structure, big consequences. Use this asset for integumentary system lectures in anatomy and histology courses, for dermatology teaching files on hair-shaft disorders, and for patient education materials explaining cosmetic hair damage versus follicular alopecia on the scalp. It also suits medical publishing layouts that need a clean, labeled schematic of the hair shaft (pilus) without relying on micrographs. Anatomical accuracy verified by SciePro's Medical Advisory Board.