L31 - Basic physiology of skin and Mechanisms of skin diseases Flashcards
List the 5 functions of the skin?
- Thermo-regulation
- Repair of injury
- Immunological defense
- Endocrine function
- Psychosocial function
List the functions of the skin as a physical barrier?
- Prevent loss of water, electrolytes
- Minimize harm by toxic materials
- Prevent infiltration by microorganisms
- Prevent entrance of allergens
- Protect against UV
Describe the effects of Toxic epidermal necrolysis (TEN)?
full-thickness epidermal cell death
Septic shock most likely caused by drug reaction
List conditions/ diseases that arise from defective skin barrier against dehydration and electrolyte loss?
pre-renal failure, hypotension, hypernatraemia
List 3 types of erythroderma?
psoriasis, eczema, drug eruption
Which layer of the skin acts as a barrier to toxic materials?
Stratum corneum (SC): Dead keratin envelope
Name some conditions that cause defective stratum corneum in skin. Consequences?
Disorders of keratinization
e.g. Darier’s disease, epidermolytic hyperkeratosis
– Less resistant to chemical penetration
– Recurrent bacterial infections
Describe the pathogenesis of Atopic dermatitis?
Loss of function filaggrin gene mutation**
> > lack of ceramides (sphingolipids)
> > more transepidermal water loss
> > epi-cutaneous sensitization by allergens)
Which components of the skin protect against UV light?
– Stratum corneum (reflect, scatter photons)
– Melanin (absorb photons)
Mechanisms of skin thermo-regulation in response to heat?
evaporative cooling, vasodilatation, direct radiation
What type of gland is Eccrine gland? Function and discribution?
Sweat glands for evapourative cooling: secrete hypotonic sweat
Generalized distribution, densely populated in palms, soles, axillae
Mechanisms of skin thermo-regulation in response to coldness?
Muscle exercise (voluntary)
Shivering (involuntary)
Vasoconstriction
Compare the repair capacity of the epidermis and dermis of skin?
– Epidermal = complete regeneration
– Dermis = granulation (scarring)
Define the 3 pathways for complement activation?
- Classical pathway (antigen-antibody complex)
- Alternative (polysaccharides, bacterial cell wall)
- Lectin pathway (microbial carbohydrates)
Name one complement that opsonizes microbes? Name 3 for increasing vascular permeability?
C3b (opsonin)
C3a, C4a, C5a (anaphylatoxins)
Which complements for the membrane attack complex?
Assembly of C5b, C6, C7, C8, C9 = membrane attack complex (MAC)
makes pores in cell membrane = osmotic lysis
Give 2 examples of anti-microbial peptides of skin? Which layer secretes?
– Human β-definsin (HBD) –HBD 1,2,3,4
– Dermocidine
Secreted from epidermis
Which condition is caused by increased expression of HBD-2?
Human β-definsin -2
> > Psoriasis (less bacterial infection observed in these patients)
Function of the skin in the Vitamin D metabolism pathway?
Converts 7-dehydrocholesterol to cholecalciferol (vitamin D precursor)
Describe the effects of glucocorticoids on the skin?
Glucocorticoids: Loosen intercellular connections and reduce epidermis effectiveness
Describe the effects of sex hormones on the skin?
Sex hormones:
- increases epidermal thickness
- accelerate wound healing
- increase dendritic cells protecting against cancer cells
List 4 skin diseases that affects the appearance of skin and psychosocial function?
- Alopecia = hair loss
- Vitiligo (white patches of skin)
- Albinism
- Psoriasis (scaly plaques)
Clinical presentation of atopic dermatitis? Acute, subacute and chronic lesions?
- Ill-defined erythematous scaling patches**
- Highly sensitive to allergens (increased serum total IgE)
Acute lesions: swelling, vesicles
Subacute lesions: discoid-shaped, weeping
Chronic lesions: lichenification
List 4 causes/triggers of Psoriasis?
- Genetic: familial component
- Inflammation: cytokines (IL-1, IL-6…)
- Drugs: Alcohol, hydroxychloroquine, terbinafine, lithium, β blockers
- Infections: Strep., HIV
Clinical presentation of psoriasis?
- Well-demarcated erythematous scaling plaques on extensor surfaces, scalp
- Nail changes: Pitting, Onycholysis (separation of nail from nail bed)
- Association with arthropathy (joint pain)
Clinical presentation of contact dermatitis?
Usually well-defined border: itchiness, erythema, scaling
Confined to areas with exposure to culprit (e.g. hair dye, ring, cosmetics)
Acute: weeping, vesicles
Define the 2 types of contact dermatitis?
- Irritant contact dermatitis (more common)
2. Allergic contact dermatitis: Type IV HSR
Compare between impetigo and erysipelas: Causative pathogen, appearance and affected body part?
Impetigo:
- Staphylococcus aureus
- Yellow- / honey-colored crusts
- Peri-oral areas
Erysipelas:
- Streptococcus pyogenes
- Well-defined, red, painful patches on face
Compare between impetigo and erysipelas: extent of skin involvement and complications?
Impetigo:
- Superficial epidermis
- Complications: Bullous impetigo, Staphylococcal scalded skin syndrome
Erysipelas:
- Dermis with lymphatic spread
- Complications: Lymphedema, Post-streptococcal glomerulonephritis
List 2 viruses that causes cutaneous infections?
HSV: HSV-1 = herpes labialis, HSV-2 = Genital herpes
VZV: chickenpox, Herpes Zoester
List 3 dermatophytes (fungal) that cause cutaneous infection? Which layer of skin is involved?
Trichophyton, epidermophyton, microsporum
Superficial fungal infection of skin: stratum corneum / hair / nail (keratin layer)
Name 2 skin conditions caused by dermatophyte infection?
Tinea cruris: groin
Tinea pedis: feet
List 2 non-dermatophytes fungi that cause skin infection?
Candida, Fusarium
Clinical feature of fungal skin infection?
Annular scaling patches with advancing border
Name one parasitic cutaneous infection?
scabies infestation:
hypersensitivity to mites (Sarcoptes scabiei) and their droppings
Epidemiology of scabies infestation?
elderly patients in elderly homes, hospitals
e.g. by infected bedsheets, clothing
Clinical features of scabies infestation?
Severe itchiness
Discrete papules on limbs / trunk
Burrows, pustules
