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Chapter 4

Chapter 4. Pages 102 - 104. Hairs and Hair Follicles. Appendage of the skin There are millions of hairs covering most of your body Specific areas of hair play protective roles (for example, eyelashes), but most of the hair on your skin has lost its protective quality

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Chapter 4

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  1. Chapter 4 Pages 102 - 104

  2. Hairs and Hair Follicles • Appendage of the skin • There are millions of hairs covering most of your body • Specific areas of hair play protective roles (for example, eyelashes), but most of the hair on your skin has lost its protective quality • Originally helped keep your body warm by providing insulation for cold weather

  3. Hairs and Hair Follicles, cont’d. • A hair is a flexible epithelial structure • Produced by a hair follicle • The portion enclosed in the hair follicle is called the root • The portion extending from your scalp or skin is called the shaft • Hair is formed by the division of well-nourished germinal epithelial cells in the growth zone or matrix of the hair bulb at the end of inferior end of the hair follicle • As the daughter cells are pushed farther away from the growing region of the follicle they become keratinized and die • The bulk of the hair shaft is dead material

  4. Hair and Hair Follicles, cont’d. • Each hair consists of a central core called the medullah • The medullah is surrounded by a cortex layer • The cortex is enclosed by an outermost cuticle formed by a single layer of cells that overlap each other like shingles on a roof • Helps keep the hairs apart to prevent matting • Cuticle is the most heavily keratinized region • Provides strength and keeps the inner layers tightly compacted

  5. Hair and Hair Follicles, cont’d. • The cuticle is very easily damaged, especially at the tip of the shaft • The constant damage leads to a fraying of the fibers • “split ends” • Hair pigment is made by melanocytes in the hair bulb • Varying amounts of different melanin produces a wide variety of colors from pale blonde to pitch black • Hairs also come in a variety of sizes and shapes • Short for the eyebrows, long for the head, and usually nearly invisible on your arms, back, etc.

  6. Hair and Hair Follicles, cont’d. • The shape of the hair shaft determines the type of hair a person has • Oval = wavy hair • Flat and ribbonlike = curly hair • Round = straight • Hair is among the fastest growing tissues in the body • Humans are born with the number of hair follicles they will have for their entire lives • Hormones account for the sudden growth of hair in specific regions

  7. Hair and Hair Follicles, cont’d. • Compound structures (made up of more than one part) • Inner layer/sheath is composed of epithelial tissue and forms the hair • Outer layer/sheath is dermal tissue • Supplies blood vessels to the epidermal portion and reinforces it • Papilla of the hair follicles provide blood supply to the growth region of the hair bulb

  8. Hair and Hair Follicles, cont’d. • Your hair follicles are slanted for a reason • The ArrectorPili are smooth muscle cells that connect each side of the hair follicle to the dermal tissue • When the muscles contract the hair is pulled upright, creating goosebumps • Usually occurs when people or animals get too cold or are scared • Provides an extra layer of insulation for animals during cold weather, but doesn’t do much to help humans keep warm because our body hair is so thin • A scared cat is probably the best example of an organism’s reaction to fear

  9. Nails • Fingernails and toenails are scale-like modifications to the epidermis that correspond to the hoof or claw of other animals • Each nail has a free edge, a body, and a root • Body: visible attached portion • Root: embedded in the skin • Borders of the nails are covered by skin folds, called nail folds • The thick region of this is commonly called the cuticle

  10. Nails, cont’d. • The nail bed is made of stratum germinativum (from the epidermis) • The thickened part of the stratum germinativum is called the nail matrix • The nail matrix is responsible for the growth of the nail • Just like hair, your nails are made up of mostly dead material – as the nail moves away from the matrix it becomes increasingly keratinized and dies • Nails are transparent and nearly colorless, but look pink because of the blood supply of the dermis • The exception to this is the nail matrix which appears as a white crescent and is called the lunula

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