topical infections skin Flashcards
functions of skin
- physical barrier to noxious agents and entry of pathogens
- immunological barrier to the entry of pathogenic organisms
- assists retention of heat and regulation of temperature
- retains moisture and maintains osmotic balance within body
- sensory organ
- excretion of sweat/salt balance, pheromones, antibacterial peptides
- vitamin D production
- protection from UV by melanocytes producing a pigment
skin structure
- waterproof cornified outer layer of keratin proteins and lipids, made by epidermis
- hair follicle with sebaceous gland and muscle in dermis
- heat insulating fatty layer of hypodermis
- apocrine sweat glands: bud fatty secretions off into enclosed areas like hair follicles
- eccrine sweat glands: secrete directly onto skin surface (thermoregulation, salt excretion, antibacterials)
layers of the epidermis
- germinal layer: stem cells replicate + renew migrating upwards / melanocytes produce pigment
- spindle layer: cells glued onto a sheet-like structure containing langerhans cells
- granular layer: vesicles containing keratin fibre which strengthens layer
- anuclear squamous layer: tough because of tightly joined keratin, dead skin cells constantly shed off
the pilosebaceous unit
- hair follicle bases is in the dermis layer
- the arrector muscle: when it contracts it pulls the base upright making the hair stand up
- sebum is produced (sticky substance) it is antibacterial with low pH containing proteins/waterproofing lipids
sensory nerves in the skin
- the meissner corpuscle: responds to light pressure
- pacinian corpuscles: deeper pressure
- merkel cells: respond to sustained light pressure
4 stages of wound healing
- haemostasis
- inflammation
- proliferation
- remodelling
haemostasis
- fibrin is released by platelets
- cross linked to make a plug to stop bleeding
- preventing infections
- langerhan cells patrol local area
- neutrophils recruited
- release of histamine causes vasoconstriction
inflammation
- chemotactic factors released into bloodstream
- monocytes move by diapedesis
- more neutrophils attracted
- mast cell activation
- cycle of inflammation
- combats opportunistic infections
proliferation
- forms scab on top of wound
- scab detaches as skin regrows
- endothelial cell proliferation promotes angiogenesis (development of new blood vessels)
- fibroblast proliferation fills underlying connective tissue and skin
remodelling
- wound edges corm contiguous barrier
- healing continues underneath
- myofibroblasts make pseudopods and migrate forward dragging cells behind them
- enabling ends to come together
- takes months to fully heal
factors directly affecting wound healing
- body site
- infection
- vascular supply
- oxygenation
- mechanical stress
- desiccation (removal of moisture)
- oedema (build up of fluid causing swelling)
factors indirectly affecting wound healing
- age
- hygiene
- diabetes
- autoimmune diseases
- venous stasis (inflammation lower legs)
- predisposition to keloids
- genetic skin diseases
- immunocompromised state (AIDS/cancer)
- obesity/immobility/neuropathy
- alcoholism/drugs abuse
tanning
- UV light exposure induces double-stranded breaks in DNA in keratinocytes
- activating p53 protein
- transcription of proopiomelanocortin (POMC)
- POMC cleaved into Beta-endorphin (local analgesic) and Alpha-melanocyte stimulating hormone (MSH)
- MSH causes melanocytes to produce pigment which is transferred to keratinocytes by melanosomes
melanomas
- arise from transformed melanocytes
- hardest to treat
- invasive and needs early detection
- triggered by UV
non-melanoma skin cancer
- very common
- removed by freezing off
- not as dangerous as melanoma
squamous cell carcinoma
- top layer of epidermis
- forms as a lesion on top of skin
- common on nose/forehead/top of head
basal cell carcinoma
- germinal layer of skin then invades tissue
vesicles
fluid filled blisters the size of a pin head
bullae
fluid filled blister-like eruptions around 1cm in diameter
acne vulgaris
causes: blockage of the pilosebaceous unit can allow infection (propionium bacterium acnes) and formation of pustules
symptoms: if infection severe and hair follicle ruptures can cause scarring
treatment: topical benzoyl peroxide, tetracycline considered if symptoms severe
impetigo
causes: s. aureus, s. pyogenes
symptoms:
- non-bullous type has pinhead pustules on red skin which erupt to give yellow-brown crust (after injury)
- bullous type has larger blisters which release clear yellow liquid to leave golden yellow crust (s. aureus)
treatment: topical treatment with bacitracin or mupirocin
ecthyma
causes: progresses from untreated impetigo
symptoms: infection penetrates to deeper layers of skin causing appearance of painful ulcers
treatment: warm compresses and antibiotics (dicloxacillin)
folliculitis
causes: infection of hair follicles by s. aureus, affects beard/armpit/back of neck
signs and symptoms: red pustules form and rupture in a few days
treatment: self-limiting and resolve naturally, topical clindamycin and erythromycin if necessary and anti-bacterial soap, larger abscesses may be surgically removed
erysipelas and cellulitis
causes: involves lymphatic vessels, erysipelas caused by s. pyogenes and cellulitis by s. aureus
symptoms: painful, warm, red swelling forming well defined plaque
treatment: erysipelas: penicillin, cellulitis: dicloxacillin
necrotising fasciitis
causes: infection of subcutaneous tissue can occur after surgery/trauma, can be caused by s. pyogenes or mixture of bacteria
symptoms: warm red skin but lesion rapidly expands and tissue becomes dark, pustular then necrotic with gangrene
treatment: surgical intervention with parenteral antibiotics
mycobacteria
lupus vulgaris: brown nodules on face
leprosy: brown nodules, white patches on skin and neuropathy
fungal infections of the skin
- dermatophytosis
- trichophyton rubrum is most common infectious fungus
- fungal infections involve: trichophyton, microsporum, epidermophyton
forms of tinea
- tinea pedis (athletes foot)
- tinea cruris (jock itch)
- tinea capitis (cradle cap in babies)
- tinea corporis (ringworm)
- tinea unguium (onychomycosis) infection of nails
topical treatment: terbinafine/clotrimazole/econazole
tinea versicolor
causes: widespread yeast malasseiza furfur more common in hot climates
symptoms: lightened pigmentation of the skin in upper body/limbs
treatment: selenium sulphide shampoo or topical antifungal agents
candidiasis
causes: yeast candida albicans (normal microbiota), poor oral hygiene and dentures
symptoms: inflamed and itchy membranes in moist mucous tissues such as mouth/vagina/armpits
treatment: topical antifungals, systemic antifungals such as ketoconazole/fluconazole
herpes simplex (type 1) and cold sores
causes: antibodies to HSV type 1, virus resides in dorsal ganglia until reactivated
symptoms: self limiting eruption around mucous membranes of mouth
treatment: aciclovir favoured treatment
herpes varicella zoster (chicken pox/shingles)
causes: virus travels to sensory ganglia where it remains for life
symptoms: pain, paraesthesia (burning sensation) in an affected dermatome
treatment: resolves with rest and analgesics, aciclovir can be used
warts
- benign skin tumours caused by HPV
- have dark necrotised blood vessels at heart of wart
- common wart affects hands/face/knees and can spread
- plantar wart grows into skin of foot causing pain
- can resolve but can be removed by chemical cryo/surgical ablation
- genital warts can increase risk of cervical cancer
molluscum contaginosum
causes: pox virus, transmitted by direct skin contact
symptoms: hyperplasia raised pink, pus filled lesions with central depression
treatment: can linger in immunocompromised individuals similar treatment options for warts with addition of curettage and cantharidin
