Quick Facts
The hair shaft is the long cylindrical part that is the major portion of a hair, sometimes referring to only the portion that extends beyond the surface of the skin (Dorland, 2011).
Structure/Morphology
The hair shaft is composed of three concentric layers, namely the outer cuticle, middle cortex, and inner medulla. They differ from each other in the types of keratin filaments they possess. Cells in the hair matrix surrounding the dermal papilla are responsible for hair growth.
The cuticle forms the outer surface of the hair shaft. It is made up of layers of overlapping keratinized squamous cells, which resembles fish scales. The cuticle protects the hair from physical and chemical damage. The cortex is the bulkiest layer of the hair shaft; it is composed of elongated cells containing hard keratin intermediate filaments and may contain melanin contributing to the hair color. The medulla, which is absent in fine hair, is composed of loose aggregates of cells (Standring, 2016).
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series: Elsevier Limited.
