Tissues 11 - Hair and Nails Flashcards
Hair: summarise the structure and function of hair, recall the development and structure of the hair follicle, and summarise the regulation of hair growth Nails: summarise the functions, structure and growth of nails
Where is hair found?
Over the entire surface of the skin, except the glaborous skin of palms, soles, glans penis and vulval introitus.
What are the functions of the hair?
- Protection - against UV light, eyelashes protect the eyes.
- Sensation - sensory innervation is present within the follicles
- Thermoregulation
- Communication/sexual attraction.
List the three types of hair
- Lanugo
- Vellus
- Terminal
Describe lanugo hairs and where they are found.
Lanugo hairs are fine and long, formed in the foetus at 20 weeks. Usually shed before birth - seen in premature babies and anorexic patients.
Describe vellus hairs and where they are found.
Vellus hairs are short, fine and light coloured, and cover most of the body.
Describe terminal hairs and where they are found.
Terminal hairs are longer, thicker and darker, found on the scalp, eyebrows, eyelashes, pubic, axillary (armpit ) and beard areas.
How is differentiation of a terminal hair from a villus hair stimulated?
Stimulated by androgens at puberty.
Describe the structure of the pilo-sebacious unit.
- Hair follicle is an invagination containing a hair.
- Upper section, below the sebaceous gland, is the infundibulum.
- Hair shaft includes an outer cuticle (keratinocytes) and an inner medulla
- Germinative cells in the hair bulb with melanocytes (synthesise pigment)
- Arrector pilli muscle - under autonomic control, not easily seen in humans.
- Sebaceous glands are associated with follicles, and produce sebum.
How is sebum production in adults and children different?
Adults have larger, swollen sebaceous glands, activated by androgens in puberty. They produce an oily sebum
Describe the type of secretion that occurs in sebum production.
Holocrine secretion - cells disintegrate and release their lipid cytoplasm.
Describe hair embryology.
- Hair follicle has input from the epidermis
- Epidermis also responsibe for matrix cells, hair shafta dn the dermis
- Contributes to papilla, blood vessels and nerves.
Describe the hair growth cycle.
- Rate of growth differs between sites - eyebrow hairs grow faster than scalp hair.
- 3 phases - anagen, catagen and telogen
What is the anagen phase of the hair growth cycle?
Growing phase
How long does anagen last in scalp hair compared with eyebrows?
3-7 years in scalp hair, 4 months in eyebrows.
What is the catagen phase of the hair growth cycle?
Resting phase. When the syntesis of proteins stops, the follicle retreats towards the surface.
How long does resting phase last?
3-4 weeks
What is the telogen phase of the hair growth cycle?
Shedding phase.
How is telogen phase in hair growth distinguished?
By hairs with a sort club root.
What percentage of hairs are in anagen pase, catagen phase and telogen phase at one point in time?
Anagen - 80-90% of scalp hairs
Catagen - 10-20% of scalp hairs
Telogen - less than 1% of hairs
How many scalp hairs are shed a day?
50-100
What is the nail?
A phylogenetic remanant of claws, which consists of a plate of densely packed keratin.
What is the function of nails?
To facilitate grasping and tactile sensitivity, and to protect the finer/toe tip.
What is the nail matrix?
The area beneath the nail where dividing cells keratinize, mature and form the nail plate.
What is the nail plate?
The nail - 0.3-0.5mm thick, grows 0.1mm a day in fingernails.
What is the nail bed?
The area beneath the center of the nail, which prodces small amounts of keratin to become adherent to the nail plate.
What are the adjacent dermal capillaries and the nail lunulas colours?
- Adjacent dermal capillaries are pink
- White lanula is the visible part of the matrix - the halfmoon
What is the hyponychium?
The thickened epidermis that underlies the free margin of the nail. (At the top of the nail)
