2.5: accessory structures: hair

composition

row of keratinized squamous epithelial cells

-hair is found everywhere on the body except areas of thick skin

structure of hair

-shaft: exposed to external environment, contains dead cells

-root: internal:

-hair follicle: layer of epidermal tissue anchoring root into dermis

-hair matrix: actively dividing stem cells above hair papilla (for blood supply)

-arrector pili: connected to hair follicle; smooth muscle, contract to cause piloerection

hair shaft composition

-medulla: core of loosely arranged cells made from soft keratin

-cortex: several layers of complex hard keratinocytes, site of pigmentation

-cuticle: single layer of overlapping cells, most highly keratinized region

split ends

damage to cuticle exposes underlying layers

types of hair: lanugo

unpigmented hair in developing fetus, insulative purpose

types of hair: vellus

fine, thin body hair

types of hair: terminal

thicker hairr making up eyebrows, lashes, scalp

-after puberty, terminal hair grows in pubic region

-in males, facial, trunk, limbs

texture of hair is dictated by

shape of follicle

color of hair is dictated by

melanin pigment in hair shaft: eumelanin or pheomelanin

hair growth cycle: anagen

active cell division, utilize nourishing blood supply, get pushed superficially

hair growth cycle: catagen (transition phase)

stop cell division, detaches from nourishing blood supply

hair growth cycle: telagen (resting phase)

without nourishment, hair dies & falls out

scalp hair: in anagen for __ years, high/ how mitotic rate

~6 years, higher mitotic rate

lashes & brows: in anagen for __ days, high/ how mitotic rate

~30 days, low mitotic rate