Existing cells of the hair root are pushed upward

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Existing cells of the hair root are pushed upward  hair gets longer, as they get pushed up higher  become keratinized and die Regression stage – cells in hair matrix stop dividing, hair follicles atrophy and stops hair growth Resting stage – after regression, hair follicle enters a resting period
+ Types of Hairs Hair follicles develop at ~12 weeks after fertilization Lanugo: 5 th month of development, follicles produce very fine, nonpigmented, downy hairs Cover the body of the fetus Terminal hairs: prior to birth, lanugo of the eyebrows, eyelashes and scalp are replaced – long, coarse, heavily pigmented hairs Vellus hairs: rest of the hairs on the fetus is replaced by “peach fuzz”, short, fine, pale hairs barely visible to the naked eye During childhood – hairs cover most of the body except for the hairs of the eyebrows, eyelashes and scalp
+ Hair Color Color is from the amount and type of melanin in its keratinized cells Melanin synthesized by melanocytes Dark-colored hair (brown-black): eumelanin Blond and red colored hair (yellow to red): pheomelanin Gray hair: progressive decline in melanin – very few melanin granules White hair: lack of melanin, air bubbles in the shaft
+ Skin Glands Epithelial cells secrete a substance – several kinds of exocrine glands Sebaceous glands (oil) Sudoriferous glands (sweat) Ceruminous glands (wax)
+ Sebaceous Glands Oil glands Simple, branched acinar (rounded) glands Lies in dermis, opens into neck of a hair follicle Some locations open up directly onto surface of skin (lips) Secrete sebum: mix of triglycerides, cholesterol, proteins and inorganic salts Coats the surface of hairs and helps them from drying and becoming brittle Prevents excessive evaporation of H2O from the skin, keeps skin soft Inhibits growth of some (but not all) bacteria
+ Sudoriferous Glands Sweat glands Release sweat (perspiration) into hair follicles or onto the surface of skin through pores Two types: eccrine and apocrine Eccrine – extensive distribution, terminate at pores at the surface of the epidermis, stimulated by emotional stress Involved in thermoregulation and waste removal Apocrine – limited to skin of the axillae, groin and areolae, ducts open into hair follicles Stimulated during emotional stress and sexual excitement
+ Ceruminous Glands Modified sweat glands in the external ear Produce a waxy, lubrication secretion Lie in subcutaneous layer, deep to sebaceous glands Ducts open either directly onto the surface of the external auditory canal or into ducts of sebaceous glands Cerumen: combined secretion of ceruminous and sebaceous glands, yellow in color Cerumen, together with external auditory canal: provides sticky barrier that impededs entrance of foreign bodies and insects Waterproofs the canal and prevents bacteria and fungi from entering cells
+ Nails Tightly packed, hard, dead, keratinized epidermal cells
+ Nails Functions:

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