Hair

Question 1

Structure of hair

Answer 1

highly keratinised - keratin filaments join to make strands which make the fibre of the hair
outer cuticle, medulla (terminal), cortex

Question 2

Function of hair

Answer 2

protection - UV/Injury/eyelashes for eyes
sensation - sensory innervation
identity/cosmetics/sexual attraction
thermoregulation

Question 3

Describe hair growth

Answer 3

3 phases
growth - anagen
stable - catagen - 3-4 weeks, follicle retreat towards surface - 10-20% scalp hair
deteriorate - telogen - short club root <1% scalp hair
rate depends on location - eyebrow (4 months) shorter anogen than scalp (3-7 years) 80% scalp hair , eyebrow grow faster
randomisied but synchronise in pregnancy - thin whispy hair
Androgen driven vellus - terminal (thick and pigmented), androgen sensitive - miniaturisation.

Question 4

describe the development of the hair follicle

Answer 4

3rd trimester

hair bulb is where hair shaft is produced - contains melanocytes, specialised germinal epithelium

Question 5

What is the structure of a hair follicle

Answer 5

Infundibulum (top to sebaceous gland) - Isthmus (subaceaous gland to erector pili muscle) - Suprabulbar (erector pili muscle to bulb) - bulb

Question 6

features of the pilo sebaceous unit

Answer 6

hair follicle - invag of epidermis
hair shaft
erector pili muscle - smooth muscle - sympathetic control (eg temperature)
sebaceous gland - sebum - oily so prevents infection - sensitive to androgen (increase size in puberty)