Intro 2 Flashcards
What is the function of hair?
Protection against external factors
Sebum
Apocrine sweat
Thermoregulation
Social and sexual interaction
Epithelial and melanocyte stem cells
What are the types of hair present on the body?
Terminal hairs - scalp, eyebrows, eyelashes
Velous hairs - rest of body (except palms, soles, mucosal regions of lips and external genetalia)
What are the three components of the hair cycle?
Anagen: 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 are hair follicles?
Pilosebaceous units
They are pockets of the epithelium continuous with the superficial epidermis (extensions of the dermal-epidermal junction)
Envelop a small papilla of dermis at their base
What structures interact with the hair follicle?
Arrector pilli- smooth muscle, extends at angle between surface of dermis and point in follicle wall
Holocrine sebaceous glands - open into the pilary canal -> in axillae - follicles associated with apocrine glands
What are the parts of the hair follicle?
Infundibulum - uppermost portion of the hair follicle extending from opening of sebaceous gland to surface of the skin
Isthmus - lower portion of the upper part of the hair follicle between opening of the sebaceous gland and insertion of the arrector pili muscle
Epithelium keratinisation begins with lack of granular layer named “trichilemmal keratinisation”
What is the bulge of the hair follicle?
Segment of the outer roots heath located at the insertion of arrector pili muscle
Hair follicle stem cells reside here
Migrate:
Downwards - generate the new lower Anagen hair follicle -> enter hair bulb matrix, proliferate and undergo terminal differentiation to form hair shaft and inner root sheath
Upwards - form sebaceous glands and to proliferat in response to wound healing
What is the structure of a singular hair?
Bulb: lower most portion of the hair follicle, includes the follicular dermal papilla and the hair matrix
Outer root sheath: extends along from the hair bulb to the infundibukum and epidermis, serves as a reservoir for stem cells
Inner root sheath: guides/shapes hair
Encloses follicular dermal papilla, mucopolysaccharide-rich stroma, nerve fibres and capillary loop
What is the function of the nails?
Protection of underlying distal phalanx
Counter pressure effect to pulp important for walking and tactile sensation
Increase dexterity / manipulation of small objects
Enhance sensory discrimination
Facilitate scratching and grooming
What is the structure of the nail plate?
Final production of proliferation and differentiation of nail matrix keratinocytes
Emerges from proximal nail fold
Grows at 1-3mm/month
Firmly attached to nail bed
Detaches at hyponychium
Lined laterally by lateral nail folds
What is the structure of the nail matrix?
Produces the nail plate
Lies under proximal nail fold, above bone of distal phalanx (to which it is connected by a tendon)
The lunula is the only visible portion (white moon bit on nail)
Nail matrix keratinocytes differentiate -> lose their nuclei and are strictly adherent - cytoplasm completely filled by hard keratins
Also contain melanocytes
What is an overview of psoriasis?
Chronic, immune mediated disorder
Polygenic predisposition combined with environmental triggers
Pathophysiology involves T cells and their interactions with dendritic cells and cells involvement in innate immunity, including keratinocytes
Sharply demarcated, scaly, erythematous plaques characterise the most common form. Can also effect nails
Common sites are scalp, elbows, knees, followed by nails, hands, feet and trunk
Psoriatic arthritis is most common systemic manifestation
What is the pathophysiology of psoriasis?
Stressed keratinocytes release DNA/RNA -> form complex with antimicrobial peptides -> induce cytokines (TNF-a, IL-1, IFN-a) production -> activate dermal dendritic cells
dDCs migrate to lymph nodes -> promote Th1, Th17, Th22 cells -> chemokine release, migration of inflammatory cells into dermis -> cytokine release -> keratinocyte proliferation -> psoriatic plaque
How is psoriasis managed?
Lifestyle: alcohol, smoking
Treating co morbidities
Topical therapies: vitamin D analogues, topical corticosteroids, retinoids, topical tacrolimus
Phototherapy: narrow band UVB, PUVA (psoralen and UVA)
Acitretin
Systematic immunosuppression: methotrexate, ciclosporin
Advanced therapies: PDE4 inhibitors, biologics, JAK inhibitors
What is an overview of atopic eczema?
Intensely pruritic (itchy) chronic inflammatory condition
Complex genetic disease with environmental influences
Typically begins during infancy or early childhood
Often associated with other “atopic disorders” (asthma, rhino conjunctivitis)
Acute inflammation of cheeks, scalp and extensors in infants
Flexural inflammation and lichenification in children and adults
Daily emollients and anti inflammatory therapy are cornerstone of management
Eczema = dermatitis
