Dermatology Pt 2 Flashcards
Give 6 of the functions of the hair
Protection against external factors Apocrine sweat Sebum Thermoregulation Epithelial and melanocyte Social and sexual interaction
What are the two types of hair?
Vellus and terminal
Where is vellus hair found?
Rest of body except for: palms, soles, mucosal regions of lips and external genitalia
Where is terminal hair found?
Scalp, eyebrows and eyelashes
What are the 3 steps of the hair cycle and what happens in each of them?
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
What is the pilosebaceous unit also known as?
Hair follicle
What is the function of the Arrector Pili?
Contracts to make the hair erect on the skin to generate heat
Outline the structure of hair.
Human skin contains pilosebaceous follicles and sweat glands.
Hair follicles
Pockets of epithelium continuous with superficial epidermis.
Envelop a small papilla of dermis at their base.
Where do the holocrine sebaceous glands open up into?
The pilary canal → in axillae
Where are apocrine glands found?
In the skin are in the armpits, the groin, and the area around the nipples of the breast
What is the uppermost portion of the hair follicle called?
Infundibulum - extends from opening of sebaceous gland to surface of the skin
What is the lower portion of the hair follicle called and what happens here?
Isthmus - Between opening of sebaceous gland and insertion of arrector pili muscle.
Epithelium keratinisation begins with lack of a granular layer - Trichilemmal keratinisation
What is meant by keratinaztion?
The cytoplasmic events that take place in keratinocytes that move through the different layers of the epidermis to finally differentiate to corneocytes.
What is found in the Bulge of the hair?
Hair follicle stem cells
Where and in what manner do these hair stem cells migrate?
Downward → generate the new lower anagen hair follicle → enter hair bulb matrrix, proliferate and undergo terminal differentiation to form hair shaft and inner root sheath
Upwards (distally) - form sebaceous glands and to proliferate in response to wounds
What is the hair bulge?
Segment of outer root sheath located at insertion of the APM.
What is the hair bulb?
Lower most portion of the hair follicle, includes the follicular dermal papilla and the hair matrix.
Where is the outer root sheet (ORS)?
Extends from the hair bulb to the infundibulum and epidermis.
Serves as a reservoir for stem cells.
What is the purpose of the IRS?
Guides/shapes hair
Encloses follicular dermal papilla, mucopolysaccharide-rich stroma, nerve fibre and capillary loop > Structural support
Give 5 of the functions of the nails
Protection of underlying distal phalanx
Counterpressure effect to pulp important for walking and tactile sensation
Increase dexterity / manipulation of small objects
Enhance sensory discrimination
Facilitate scratching or grooming
Where does the nail plate emerge from?
Proximal nail fold
How fast does a nail grow?
1-3mm/month
Where does the nail plate detach?
Hyponychium
What is the nail plate lined laterally by?
Lateral nail folds
What produces the nail plate?
Nail matrix
Where is the nail matrix found?
Under proximal nail fold, above bone of distal phalanx
What is the only visible portion of the nail matrix called?
Lunula
What occurs in the nail matrix?
Keratinocytes differentiate → lose their nuclei and are strictly adherent - cytoplasm completely filled by hard keratins
Also contains melanocytes
Is polygenic predisposition enough to contract Psoriasis?
No, environmental triggers are also needed (e.g. trauma, infections or medications
What is the most common form of Psoriasis characterised by?
Sharply demarcated, scaly, erythematous plaques
What are the common sites of involvement with Psoriasis?
Scalp, elbows and knees, followed by nails, hands, feet and trunk
What is the most common systemic manifestation of Psoriasis?
Psoriatic arthritis
Explain the pathophysiology of Psoriasis
Stressed keratinocytes release DNA/RNA which form complex with antimicrobial peptides (endogenous antibiotic - Psoriasin) Cathelicidins and defensins.
Induces release of cytokines - TNF-alpha, IL-1 and IFN-alpha
This activates dermal dendritic cells (dDCs)
dDcs migrate to the lymph nodes and promote Th1, Th17, Th22 cells
These release chemokines which cause the migration of inflammatory cells into the dermis
These inflammatory cells cause release of cytokines which lead to keratinocyte proliferation
This leads to a psoriatic plaque
Why do scales form on the skin during Psoriasis?
Keratin differentiation process occurs so quickly due to increased keratin proliferation that they do not differentiate correctly.