INTRODUCTION TO ANATOMY AND PHYSIOLOGY

Structure of the Hair

Hair grows through the narrow and tube-like depressions in the skin called the hair follicle. The root of the hair is surrounded by the dermal papilla which has an abundant supply of blood vessels which provide nutrients to the area. New hair is formed in the papilla and created by hair germ cells. Hairs are soft at the base and eventually harden and die as they get towards the surface. Hair functions are for protection and sensory reasons, e.g., eyelashes and eyebrows stop anything from getting in the eye and protects the bones around the eye socket – brow bone.

Hair has three stages of growth which are known as the hair cycle. The first stage of this cycle is the Anagen stage. This is the active growing stage that can last from a few weeks to a few years. This stage ends when the hair becomes detached from the dermal papilla.

The following stage is Catagen, which is the hairs transition from active to the resting stage. The hair has stopped growing and the follicle begins to shrink so that a new hair can begin to grow at the base. This brings the cycle to the Telogen stage. This is the resting stage of hair growth; the hair is now ready to shed, and a new hair has started growing beneath it.

Hair is made up of three levels. The outer layer, the Cuticle is a tough outer protective layer of the hair shaft. The cells are translucent so allows for the colour underneath to show through. The cells form scales that overlap each other similar to that of roof tiles. The cortex lies beneath the Cuticle and is the main part of the hair. The Cortex contains the colour pigments that make up the hair colour. The cells of the Cortex contain bundles of fibres and gives the hair its strength and flexibility. Keratin is also formed in this layer. The middle core of the hair is called the Medulla, which is not always present, and this section does not appear to have any function.

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