hair follicles etc

hairs or pili

flexible strands,consist largely of dead keratinized cells. hard keratin dominates hairs and nails, tougher, more durable and individual cells do not flake off,

hair follicles

fold down from the epidermal surface into the dermis. in the scalp they may extend into the hypodermis

cuticle

formed from a single layer of cells that overlap one another from below like shingles on the roof, keeps hairs apart so it doesn't mat, most heavily keratinized part of the hair, provides strength and keeps the inner layers tightly compacted. tends to take most abrasion, tends to wear away at the tip of hair shaft, allowing keratin fibrils in the cortex and medulla to frizz out ( split ends)

alopecia

hairs are not replaced as fast as they are shed, process usually begins at the anterior hair line and progresses posteriorly, terminal hairs are replaced by vellus hairs

things that may cause hair loss or thinning

high fever, surgery, antidepressants, excessive vitamin a, blood thinners, anabolic steroids, chemotherapy, and severe emotional stress

hair pigment is made by

made by melanocytes at the base of the hair follicle and transferred to the cortical cells. vigorous portions of melanins of different colors combine to produce hair color. red hair color is pigmented by trichosidern, gray and white is from decreased melanin production and replacement of air bubbles in the hair shaft

hair papilla

nipple like bit of dermal tissue, protrudes into the hair bulb, contains a knot of capillaries that supply nutrients to growing hair and signals it to grow except for its specific location

hair matrix

actively dividing area of the hair bulb that produces the hair, originate in a region called the hair bulge

hair follicle wall is composed of

an outer connective tissue root sheath derived from the dermis, thickened basement (glassy membrane), and an inner epithelial root sheath

arrector pilli

associated with each hair follicle is a bundle of smooth muscle cells, contracts and pulls the hair follicle in an upright position and dimples the skins surface to produce goose bumps in response to cold external temperatures or fear. important to animals to retain heat and protect themselves

vellus hair

body hair of children and adult females, is fine, pale, and thin

cortex

bulky layer surrounding the medulla, consists of several layers of flattened cells

hair has three concentric layers of keratinzed cells

central the medulla, cortex, and

shaft

chief region of hair,where keratinization is complete, projects from skin, extends half way down the portion of the hair embedded in the skin, shaft is flat and ribbon like in cross sections hair is kinky, oval is silky and wavy, perfectly round its straight and course

terminal hair

coarser longer hair, may also be darker, found on scalp and is eyebrow hair, at puberty is found in pubic and axillary areas, grow in response to androgens

medulla (middle)

consists of large cells and air spaces only part of hair that contains soft keratin, is absent in fine hairs

hair bulb

deep end of the follicle is 4mm below the skin surface

cure for male pattern baldness

drugs that inhibit testosterone production(decrease sex drive)minoxidil or finasteride but must be taken daily if stop the hair that has grown will fall out

hair growth

is dependent on hormones and nutrition, poor nutrition causes poor hair growth, chronic physical irritation causes an increase in hair growth, women can get electrolysis to remove unwanted hair growth

hair follicle receptor ( or root plexus)

knot of sensory nerve endings, wraps around each hair bulb, bending the hair stimulates these endings

hair bulge

located a fraction of a millimeter above the hair bulb. chemical signals diffusing from the papilla reach the hair bulge, some of its cells migrate toward the papilla, where they divide to produce the hair cells, as new cells are produced by the matrix, the older part of the hair is pushed upward and its fused cells becomes increasingly keratinzed and die.

hair acts like

sensitive touch receptors

male pattern baldness

true or frank baldness, genetically determined, sex influenced condition, thought to be caused by a delayed reaction that switches on in adulthood and changes the response of the hair follicles to DHT (metabolite of testosterone) follicle hair cycles become so short that hairs never even emerge from the follicles before shedding and those that do are vellus

electrolysis

using light energy or electricity to destroy the hair at the roots

types of hair

vellus hair and terminal hair

root

where keratinization is still ongoing, remainder of hair deep within the follicle