Introduction to Dermatology 2 Flashcards
What external factors does the hair help protect against?
UV, things which may be crawling on us
What is the pilosebaceous unit?
the hair shaft, the hair follicle, the sebaceous gland, and the erector pili muscle
What does the pilosebaceous unit produce?
Sebum (oil)
What are the functions of the hair?
- Sexual /social interaction
- Source of epithelial and melanocyte stem cells
- Apocrine swear which is involved in thermoregulation
- Sebum production
- Protection against external factors
Where are terminal hairs found?
Scalp, eyebrows and eyelashes
Where are the vellus hairs found?
Found on the rest of the body, with the exception of the palms, soles and external genitalia, mucosal region of lips
What are the hairless genitalia in men and women?
Men - foreskin of the penis
Women- Labia minora
What are the three stages of the hair cycle?
Anagen
Catagen
Telogen
What phase of the hair cycle most of our hair in at any given time?
The anagen phase
How long does the anagen phase of the hair cycle last?
Lasts 2-6 years
What occurs in the catagen phase?
When the hair is shrinking / regressing back into the follicle
How long does the catagen phase last?
Lasts 3 weeks
What happens in the telogen phase?
The resting phase - hair is neither growing or shrinking
During states of illness, in what phase of the hair cycle can an increase in the amount of hair in this cycle be seen?
The telogen phase
How long does the telogen phase of the cell cycle last?
3 months
What happens to the hair after the telogen phase comes to a end?
The hair detaches and is lost
What are hair follicles?
Pockets of epithelium that are continuous with superficial epidermis
What is found at the base of a hair follicle?
A dermal papilla, made of dermis
Where does the arrector pili extend from?
The surface of the dermis to a point in the follicle wall
What is the purpose of the arrector pili muscle?
When they contract, they cause the hair to stand up
What type of muscle is the arrector pili?
Smooth muscle - controlled by autonomic nervous system
What type of secretion do sebaceous glands support?
Holocrine section
Where do the holocrine sebaceous glands open into?
pilary canal
In the axillae, what type of secretion are the glands found there associated with?
Apocrine glands
What are the two parts of the hair follicle?
Infundubulum and Isthmus
From what point does the infundubulum extent to and from?
The sebaceous gland to the surface of the skin
What points does the isthmus extend from?
Between the opening of the sebacous gland and the insertion of arrector pili muscle
What does epithelial keratinization begin with?
A lack of granular layer
What is trichilemmal keratinization?
Epithelium keratinisation begins with lack of granular layer names “trichilemmal keratinisation”
Where is the bulge located?
Just below the sebaceous gland
What cells reside in the bulge?
hair follicle stem cells
What forms when hair follicle stem cells migrate downwards?
New lower anagen hair follicles - they enter the hair bulb matrix, proliferate and undergo terminal differentiation to form hair shaft and inner root sheath
What forms when the hair follicle stem cells migrate upwards?
Form the sebaceous gland
Why are hair follicle stem cells important in injury?
They proliferate in response to wounding, and help healing response
What is the bulb?
The lower most portion of the hair follicle which includes the follicular dermal papilla and the hair matrix
What is the matrix?
The principal place where the hair shaft is being produced
What does the outer root sheath do?
Serves as a reservoir of stem cells
Where does the outer root sheath extend from?
From along the hair bulb to the epidermis
What is the purpose of the inner root sheath?
To guide and shape the hair
What is contained with the inner root sheath?
Follicular dermal papilla. mucopolysaccharide-rich strome, nerve fibre and capillary loop
What is the purpose of the mucopolysaccharide-rich strome found in the inner root sheath?
To give the inner root sheath strength
What do the nails protect?
The underlying distal phalanx
What are the functions of the nails?
- Protects underlying distal phalanx
- Counterpressure effect - important for walking and tactile sensation
- Increase dexterity / manipulation of small objects
- Enhance sensory discrimination
- Facilitate scratching / grooming
What is the nail plate?
The final product of proliferation and differentiation of nail matrix keratinocytes
What does the nail plate emerge from?
Proximal nail fold
What is the growth rate of the nail plate?
1-3mm a month
What is the point at which the nail plate detaches from the nail bed called?
Hyponychium
Where is the nail plate manufactured?
In the nail matrix
What is the lunula?
only visible portion of the nail matrix
Where is the nail matrix found?
Underneath the proximal nail fold, above bone of distal phalanx