Give an account of the structure of the hair. Write its function.

Hair:
• The hair is found only in the skin of mammals which are ectodermal in origin.
• The hair is situated in a hair follicle which is formed as in invagination of the stratum germinativum.
• The base of the hair follicle is everted cup-like which encloses a hair papilla or dermal papilla. The hair papilla is made up of blood vessels & the nerves.
• The hair consists of two parts viz.-hair shaft & hair root.
• The cells of the hair root divide constantly causing the growth of the hair follicle.
The part of the hair shaft inside the hair follicle is covered by two sheaths viz.
1. Huxley's sheath — Outer
2. Henle's sheath — Inner & made up of cuboidal cells
• The exposed part of the hair shaft is dead due to the deposition of the keratin protein.
• Structurally, the hair shaft consists of three parts viz.
1. Cuticle — Outermost & made up of squamous cells.
2. Cortex — It is the outer part which contains melanin pigments. The melanin pigments are absent in the hair of the rabbit.
3. Medulla — It is the central part of the hair follicle. The lanugo is without medulla.
• There is an arrector pili muscle which is attached between the epidermis & the hair follicle.
• The contraction of this muscle results in raising of hair which is a reflex action and called as goose flesh or cutis lsernia.
• This process is stimulated by the adrenalin hormone. The grey hair is without melanin pigments and its medulla develops air cavities which provide shine to the hair.