Introduction to dermatology Flashcards
Morphology of the skin
The skin can be divided into epidermis, dermis, subcutis, and adnexa (hair follicles, sebaceous, sweat and other glands, horns and clowns).
Four layers of the epidermis of skin
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stratum basale (basal layer),
stratum spinosum (spinous layer),
stratum granulosum (granular layer),
stratum corneum (horny layer).
(Haired skin has a fifth layer called the stratum lucidum between the strata granulosum and caorneum)
Cells found in the epidermis
keratinocytes (~85%),
melanocytes (~5%),
Langerhan’s cells (~5-8%),
Merkel cells (~3-5%).
What does the dermis consist of?
Collagen and elastic fibrils
Which layer of the skin has no blood vessels?
The epidermis
Phases of hair growth
Anagen
Catagen
Telogen
Anagen
the phase where mitotic activity and growth occur.
The shaft of the hair is long and the hair root or bulb deep in the dermis.
The opening of the sebaceous gland is about a third of the way down the follicle.
Catagen
a transitional phase at which growth has ceased and the follicle begins to shorten preparatory to shedding of the old hair and the regrowth of a new hair.
There are changes in the attachment of the hair shaft to the root sheath associated with this process and the follicle is shorter.
Telogen
a resting phase.
The follicle is very short, the hair shaft is separating from the root sheath preparatory to being shed and the base of the follicle is at the same level as the sebaceous gland.
There will be a new root germ deep in the dermis beneath the old follicle often already producing a new hair, which will push out the old one
It is only when follicles become ‘stuck’ in telogen that alopecia develops.
Factors influencing state of skin and hair growth
Photoperiod
Aging
Temperature
Nutrition
Calorie, lipid, and mineral intake
General disease states
Photoperiod and hair growth
Photoperiod acts via the hypothalamus, pituitary and pineal glands.
The photoperiod is particularly important with hair growth maximum in summer and minimal in winter.
Hair tends to be shed noticeably in spring and autumn.
Crust
Irregular skin surface with dried exudate (erythrocytes, leucocytes, platelets, scales, bacteria).
E.g. chronic stage of epidermitis or dermatitis.
Comedo
A greasy plug in a sebaceous follicle composed of a mixture of keratin, sebum and bacteria.
It usually has a black appearance. E.g. hyperadrenocorticism. Schanuzer comedo syndrome.
Cyst
Cavity lined by epithelium and filled with liquid or semisolid material.
E.g. dermoid cyst, follicular cyst.
Depigmentation
Loss of pigmentation.
E.g. copper deficiency.
Erosion
Partial loss of the epidermis.
The area is depressed, moist and glistening.
E.g. secondary to surface trauma, viral infections.
Erythema
Increased redness of the skin caused by capillary dilation.
E.g. dermatitis.
Epitheliotropic lymphoma
Necrosis - cell death
Dermatitic
Vasculitis and thrombosis
Excoriation
Loss of epidermis
E.g. scratch
Fissure
Linear crack or break in the epidermis
E.g. digital hyperkeratosis
Hyperpigmentation
Increased production of melanin or increase in the number of melanocytes.
E.g. chronic dermatitis and endocrine dermatosis.
Hypopigmentation
Decreased pigmentation of skin.
E.g. congenital
Lichenification
Rough, thickened skin, secondary to chronic rubbing, scratching or irritation.
E.g. chronic dermatitis.
Macule
Change in the colour of the skin, neither depressed nor elevated, circumscribed area >1 cm in diameter.
E.g. vitiligo, haemorrhage.
Nodule
Circumscribed, solid, elevated skin lesions >5 mm in diameter.
E.g. deep bacterial or fungal infections.
Papule
A palpable elevated, firm, circumscribed area <5 mm in diameter.
E.g. insect bite, superficial folliculitis.
Plaque
Elevated, firm, flat lesion >1 cm in diameter.
E.g. calcinosis cutis.
Pustule
(microabscess).
Elevated superficial accumulation of pus within or beneath the epidermis or within a pilosebaceous follicle.
E.g. bacterial infections, pemphigus foliaceous.
Scale
Flaky skin, irregular, thick or thin, dry or oily with fragmented keratinized cells.
E.g. nutritional deficiencies, fungi.
Seborrhea
Increased epidermal cell turnover, keratin scales, and acanthosis
Skin callus
Thick, hard, hairless, hyperpigmented skin area.
Common in large dog breeds over bony prominence (e.g. elbow).
Ulcer
Complete loss of epidermis.
Complete loss of epidermis and basement membrane with exposure of dermis, concave red area.
E.g. autoimmune skin diseases, feline herpesvirus infection.
Vesicle and bulla
Elevated, fluid-filled cavities within or beneath the epidermis.
Vesicle <1 cm in diameter, bulla is >1 cm in diameter.
E.g. viral infections, immunomediated diseases, burn.
Wheal
A transient, edematous, circumscribed area.
E.g. allergic reaction, insect bites.
Acantholysis
The separation of the cells of the prickle-cell layer of the epidermis from each other, resulting in the formation of clefts.
E.g. pemphigus.
Acanthosis
A thickening of the stratum spinosum of the epidermis, is the result of hyperplasia of the epidermis.
E.g. papillomas.
Apoptosis
A programmed cell death.
Atrophy
A wasting or shrinking of a cell, tissue, organ or part of an organism, after it has developed completely and achieved its full size.
E.g. dermal atrophy due to hypercortisolemia and chronic ischeamia, where a decrease in the quantity of collagen fibrils and fibroblasts is found.
Ballooning degeneration
An intracellular edema of cells in superficial layers of the epidermis, found mainly in viral infections.
E.g. pox viruses.
Calcinosis
Cutis - calcium in the dermis e.g. hyperadrenocorticism or Cushing disease.
Circumscripta - calcium over pressure points.
Collagen degeneration
Collagen flame figure
Dermal deposition of amorphous eosinophilic material on collagen fibrils.
E.g. eosinophilic granuloma, mast cell tumour.
Collagen dysplasia
An inherited abnormality of collagen resulting in decreased tensile strength and increased stretchability.
Dermatitis
An inflammatory condition of the skin, which affects primarily the dermis.
E.g. viral, bacterial infections.
Dermatophytosis
(ring worm)
Alopecia, Fungi (arthrospores), hyperkeratosis.
Desmoplasia
Fibroplasia and collagenous stroma induced by neoplastic process.
Dyskeratosis
An abnormal and premature keratinization of epidermal cells.
E.g. Zinc-responsive dermatosis.
Epidermal hyperplasia
An increase in the cells within the epidermis.
E.g. chronic dermatitis, papillomas, calluses.
Epidermatitis
Inflammation of the epidermis.
E.g. bacterial, viral, fungal, parasitic infections.
Alopecia - loss of hair, erosion - partial loss of epidermis.
Exocytosis
Migration of leukocytes and/or erythrocytes into the epidermis.
E.g. epidermitis.
Fibroplasia
Proliferation of fibroblasts and newly collagen fibrils.
E.g. response to ulceration.
Folliculitis
Inflammation within one or more follicles.
Leads to loss of hair shaft.
E.g. demodicosis.
Furunculosis
Rupture of follicle, accompanied by leakage of follicle contents, hair, keratin, sebum into the dermis, with a foreign body inflammatory response.
E.g. anal furunculosis in the German Shepherd dog.
Hidradenitis
An inflammatory response in apocrine glands (epitrichial).
E.g. bacterial infections.
Hydropic degeneration
Fluid accumulation within the basal cells and basal keratinocytes of the outer root sheath of hair follicles.
E.g. lupus erythematosus, drug eruptions, viral diseases (poxvirus).
Hypergranulosis
An increased thickness of the granular cell layer.
E.g. hyperkeratosis.
Hyperkeratosis
An increase on the thickness of the stratum corneum.
Scaly, flaky skin.
Can be thick or thin, dry or oily, with fragmented keratinized cells.
Orthokeratotic hyperkeratosis
Hyperkeratosis where the cells are anuclear
Parakeratotic hyperkeratosis
Hyperkeratosis where the cells are nuclear
E.g. vitamin A deficiency, zinc-responsive dermatosis
Necrosis
Death of cells, where there is nuclear pyknosis, karyorrhexis or karyolysis.
E.g. thermal burns.
Panniculitis or adipositis
An inflammatory change in the subcutaneous fat.
E.g. bacterial infections, foreign bodies.
Perifoliculitis
An inflammation of a follicle and the connective tissue surrounding it.
Perivasculitis
Allergic skin dermatitis: food allergy, atopy, flea allergy, contact dermatitis, photosensitisation, etc.
Pigmentary incontinence
Loss of melanin from the stratum basale and the accumulation of the pigment in macrophages in the upper dermis.
E.g. lupus erythematosus, dermatomyositis, erythema multiforme.
Pustule or miscroabscess
A small elevation filled with pus that is situated within or beneath the epidermis or within a pilosebaceous follicle.
E.g. superficial bacterial infections, pemphigus foliaceus.
Sebaceous adenitis
An inflammatory reaction targeting sebaceous glands.
E.g. secondary to folliculitis
Spongiosis
Intercellular oedema.
E.g. dermatitis.
Vasculitis
An inflammation of blood vessels.
E.g. systemic lupus erythematosus.
Inflammatory pathology of the skin
Acute inflammation virus, bacteria, fungi, parasites,
/ Destructive - immune mediated.
Physical and chemical agents.
Hyperplastic pathology of the skin
Chronic conditions with inflammatory component.
Epidermal – dyskeratosis - dermal- calcification, fibrosis, granuloma formation.
Aetiology can be nutritional, infective or chemical.
Atrophic pathology of the skin
Senility hormonal disturbances - (thinning of the epidermis, dermal collagen fibrils break up, pilosebaceous atrophy).
Corticosteroids.
Neoplastic pathology of the skin
Epidermis, dermis, subcutis and metastasis.
Endocrine pathology of the skin
Most hairs arrested in telogen, less common in catagen more easily epilated by licking, rubbing, etc.
Bilateral symmetrical alopecia
Epidermal atrophy and hyperkeratosis
Sebaceous gland atrophy
