Hair Theory Flashcards
Trichology def
Study of hair
Main purposes of hair
Adornment
Protection from heat, cold, and injury
Sensory perception
Hair is derived from the ______
Epidermis
Three segments of the hair follicle
Bulb
Isthmus
Infundibulum
Bulb segment, parts, and description
Lower segment
Dermal papilla
Root sheath
Germinal matrix
Extends from base of follicle to insertion of arrector pili muscle
Isthmus segment, parts, and description
Middle segment
Arrector pili muscle
Glands
Extends from insertion of arrector pili muscle to entrance of sebaceous gland duct
Infundibulum segment, parts, and description
Upper segment
Hair strand (hair shaft)
Extends from the entrance of sebaceous gland duct to opening of the follicle; filled with sebum
Dermal papilla def
A mass of loose connective tissue located at base of the hair follicle
Germinal matrix cells def
Tiny capillaries (small blood vessels) that supply nourishment to the cells around it
Root sheath def
Inner and outer portions that help form growing hair
Outer root sheath description and contains?
Continuation of the basale layer
Surrounds the inner root sheath
Remains static
Serves as storage for stem cells
Melanocytes
Langerhans cells
Merkel cells
Inner root sheath description
Structure in the lower part of the hair follicle
Surrounds and protects growing hair
Helps hair take a shape
Three layers of the inner root sheath with defs
Henie’s layer - outermost layer of inner root sheath; single layer of cube-like cells with clear, flattened nuclei
Huxley’s layer - between cuticle and Henie’s layer; contains 1-2 layers of flattened epithelial cells
Cuticle layer - lies in the center; forms channel for growing hair; anchors hair in place
Vellus hair def
Peach fuzz
Capilli hair def
Hair on scalp (cap-calp)
Barba hair def
Beard hair (think barber)
Cilia hair def
Eyelashes
Supercillia hair def
Eyebrows
lanugo hair def
Hair at birth
Terminal hair def
Dark, coarse hair
Which stage is the 1st and longest stage of hair growth
Anagen; active stage
Which is the 2nd and shortest stage of hair growth
Catagen; transition stage
What is the 3rd stage of hair growth and what is it called/known as
Telegen; resting stage
What is the name of the area of cells around the dermal papilla
Germinal matrix
Arrector pili muscle def
Isthmus or middle segment of the follicle
Arrector pili muscle description
Extends from cells in the dermis to attach to the follicle just below the sebaceous gland and causes hair to stand up on end when a person is scared or cold
Hair root def
Portion of hair inside the hair follicle under the skin’s surface
Hair strand def
Portion of hair that extends above the skins surface
Keratinization def
Process where cells change their shape, dry out, and form keratin protein; once keratinized, cells that form the hair strand are no longer alive
3 parts of the hair strand
Medulla
Cortex
Cuticle
Medulla def
Central core of the hair strand; also called the pith or marrow; often absent in fine or very fine hair
Cortex def
Second layer, consists of unique protein structures; gives hair pigment and strength/flexibility
Cuticle def
Outer covering of the hair strand; made up of overlapping layers of transparent scales
Stratum basal layer “steps” (5)
- In fetal life, the hair follicle forms from a cluster of cells in the upper layer of skin
- The cluster of cells is called the “primitive hair germ”; it needs nourishment to grow into a fully developed hair follicle
- To get nourishment, the primitive hair germ works its way down into the lower (dermal) layer
- As the primitive hair germ works its way down, the cell cluster pulls the upper layer down with it creating a follicle
- At the base of the hair follicle is a large structure called the “papilla” which supplies nourishment to the hair bulb
Shapes of a follicle
Round
Oval
Elliptical
The shape of the follicle will determine the shape of the _______as it grows from the follicle
Hair strand
A round follicle will make what hairstrand shape
Straight hair
An oval follicle will create what hairstrand shape
Wavy or curly hair
Elliptical follicle will create what hairstrand shape
Tightly curled hair
Anagen stage description
Active or growing stage
Each hair bulb has attached to a root sheath
On average, 90% of hair is in this stage (scalp lasts 2-6 years in anagen)
Hair color is darker
Catagen stage description
Brief transitional period when all cell division stops
Shortest of the hair growth cycle
Dermal papilla breaks away; lower end of the hair comes loose from the base of the follicle
Telogen stage description
Resting stage
Hair bulb has no attached root sheath
Hair falls out
On average, 10-15% of hair is in this stage
2 factors that affect hair growth
Hirsutism
Hypertrichosis
Hirsutism possible cause and def
Polycystic ovary syndrome (PCOS) and Cushing syndrome
Excessive amounts of terminal hair found in women in areas of the body where men usually get hair: face (above the upper lip and on the chin), back, abdomen, and chest
Can affect both men and women
Hypertrichosis possible cause and def
Ambras syndrome
Abnormal coverage of hair on areas of the body where normally only lanugo or baby-fine hair appears
The average rate of human hair growth
1/2” (1.25cm) per month
Eyebrow and eyelash hair is replaced how often
4–5 months
Melanin is found mainly in the ______
Cortex; the hairstrand’s second layer
The natural coloring process
Melanocytes produce melanosomes, which contain the pigment melanin
Melanin def
Produced my melanocytes- cells that exist among the dividing cells within the hair bulb
Melanocytes def
rest near the hair bulb’s nourishment center, the dermal papilla, and form bundles of a pigment protein complex called melanosomes
Two types of melanin
Eumelanin - brown/black
Pheomelanin - red/yellow
What influences the resulting hair color
The amount, size, and distribution of one or both of the melanin types
If the amount of pheomelanin is very concentrated and near the cuticle layer, the hair color will appear more _____
Red
Lighter hair has melanin only in the
Cortex
Gray hair is caused by
Reduced color pigment (melanin) in the cortex kayaker of the hair
