human anatomy and physiology textbook pdf 11

Uppermost portion of the hair follicle extending from the opening of the sebaceous gland to the surface of the skin The lower portion of the upper part of hair follicle between the opening of the sebaceous gland and the insertion of arrector pili muscle Lowermost portion of the hair follicle, includes the follicular dermal papilla and the hair matrix Onion-shaped portion of hair bulb surrounded by hair matrix cells, consists of mesenchymally derived tissues Non-pigmented, and generally non-medullated short hairsĬonsists of rapidly proliferating keratinocytes that move upwards to produce the hair shaft Regression and involution stage of hair follicle cycleĪctive hair shaft shedding stage of hair follicle cycleįully keratinized, dead hair formed at telogen stageįine hairs on the fetus body shed in utero or within the first weeks after birth Extensive knowledge on anatomical and physiological aspects of hair can contribute to understand and heal different hair disorders. Distinctive anatomy and physiology of hair follicle are presented in this chapter.

The duration of growth and rest cycles is coordinated by many endocrine, vascular and neural stimuli and depends not only on localization of the hair but also on various factors, like age and nutritional habits. Hair follicle has a continuous growth and rest sequence named hair cycle. The hair shaft consists of a cortex and cuticle cells, and a medulla for some types of hairs. The follicle is the essential unit for the generation of hair. Hair is a derivative of the epidermis and consists of two distinct parts: the follicle and the hair shaft. Hair is one of the characteristic features of mammals and has various functions such as protection against external factors producing sebum, apocrine sweat and pheromones impact on social and sexual interactions thermoregulation and being a resource for stem cells.

Human anatomy and physiology textbook pdf 11