Intro to dermatology- Nails and Hair

Question 1

What is the function of hair?

Answer 1

Protection against external factors
Sebum
Apocrine sweat
Thermoregulation
Social and sexual interaction

Question 2

What are the 2 types of hairs?

Answer 2

Terminal hairs: found on scalp, eyebrows and eyelashes

Vellus hair: found on rest of body (except palms, soles, oral and genitalia mucosa)

Question 3

What is the hair cycle?

Answer 3

Anagen (new hair forms and grows)- 85% of hairs, lasts 2-6 years
Catagen (regressing phase)- 1% of hair, lasts 3 weeks
Telogen (resting phase)- 10-15% of hair, lasts 3 months
Then loss of old hair

Question 4

How is hair structured?

Answer 4

Human skin contains pilosebacious unit and sweat gland

Has an infundibulum, isthmus, bulge, bulb and inner root sheath

Question 5

What is the infundibulum?

Answer 5

Uppermost portion of hair follicle extending from opening of sebaceous gland to surface of skin

Question 6

What is the isthmus?

Answer 6

Lower portion of upper part of hair follicle between opening of sebaceous gland and insertion of arrector pili muscle
Epithelium keritanisation begins with lack of granular layer named ‘trichilemmal keritanisation’

Question 7

What is the bulge?

Answer 7

Segment of outer root sheath located at insertion of arrector pills muscle
Hair follicle stem cells reside here
The bulge migrates:
- downwards- generates new lower anagen hair follicle. This enters hair bulb matrix, proliferates and undergoes terminal differentiation to form hair shaft and inner root sheath
- upwards- forms sebaceous gland and proliferates in response to wounding

Question 8

What is the bulb?

Answer 8

Lower root portion of the hair follicle , includes the follicular dermal papilla and hair matrix
Its the outer root sheath
Extends from hair bulb to the infundibulum and epidermis
Serves as a reservoir of stem cells

Question 9

What is the inner root sheath?

Answer 9

Guides/ shapes hair

Encloses follicular dermal papilla, mucopolysaccharide, nerve fibre and capillary loop

Question 10

What are functions of the nail?

Answer 10

Protection of underlying distal phalanx
Counterpressure effect to pulp important for walking and tactile sensation
Increases dexterity/ manipulation of small objects
Enhances sensory discriminations
Facilitates scratching or grooming

Question 11

How is the nail structured?

Answer 11

Nail plate:
- Emerges from proximal nail fold 
- Detaches at hyponychium
Nail matrix
-Produces nail plate
-Lies under proximal nail fold above bone of distal phalanx
-Lanula is the only visible portion 
-Nail matrix keratinocytes differentiate- they loose their nuclei and are strictly adherent- cytoplasm is completely filled by hard keratinocytes
-Also contain melanocytes