Introduction to Dermatology II Flashcards
What are the functions of the hair?
● Protection against external factors
● Sebum
● Apocrine sweat
● Thermoregulation
● Social and sexual interaction
● Epithelial and melanocyte stem cells
What is the difference between eccrine and apocrine
glands?
Eccrine sweat glands occur over most of the body and open directly onto the skin’s surface.
Apocrine glands open into the hair follicle, leading to the surface of the skin. Apocrine glands develop in areas with many hair follicles, such as on the scalp, armpits and groin.
What are the two types of hair follicles?
vellus and terminal
What are terminal hairs?
scalp, eyebrows and eyelashes
What are the hairs on the rest of the body called?
vellus hairs (except palms, soles, mucosal regions of lips and external genitalia)
What is the hair cycle of the hair?
Anagen, catagen and telogen
Explain in more detail the stages of the hair cycle?
● Anagen (where new hair forms and grows)
➢ 85% of hair; 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.
What is the structure of the hair within the skin?
● Human skin contains pilosebaceous follicles and sweat glands.
● Hair follicles (pilosebaceous unit)
● Pockets of epithelium continuous with superficial epidermis
● Envelop a small papilla of dermis at their base.
What are holocrine sebaceous glands?
they open into the pilary canal–> in axillae- follicles associated with apocrine glands
How are arrector pili muscles specially adapted?
Arrector pili (smooth muscle) extends at angle between surface of dermis and point in follicle wall.
What is the hair split into?
Infundibulum
Isthmus
What is the Infundubulum?
Uppermost portion of the hair follicle extending from opening of sebaceous gland to surface of the skin
What is the isthmus?
Lower portion of upper part of hair follicle between opening of sebaceous gland and insertion of arrector pili muscle
When does epithelium keratinization start?
Epithelium keratinization begins with lack of granular layer named “trichilemmal keratinization”
What is the bulge of the hair?
● Segment of the outer root sheath located at insertion of arrector pili muscle
● Hair follicle stem cells reside here
What are the types of migration of hair?
downward and upwards (distally)
What is downwards migration?
Downward → generate the new lower anagen hair follicle → enter hair bulb matrix, proliferate and undergo terminal differentiation to form hair shaft and inner root sheath.
What is upwards (distally) migration?
Upwards (distally) → form sebaceous glands and to proliferate in response to wounding