E2

skin layers

1. epidermis

2. dermis

3. subcutaneous tissue

Epidermis

: Outer layer with protective, renewing cells.

Dermis

: Middle layer with blood vessels, nerves, and glands.

Subcutaneous tissue

: Fat layer that cushions and insulates.

layers of the epidermis

1. Stratum basale

2. stratum spinosum

3. stratum granulosum

4. stratum lucidum

5. stratum corneum

Stratum basale (basal layer)

: New skin cells form.

Stratum spinosum:

Cells start keratin production.

Stratum granulosum (granular layer):

Cells flatten and waterproof.

Stratum lucidum:

Clear layer in thick skin only.

Stratum corneum

: Dead, tough outer cells

sensory nerve ending

• meissner (tactile/ touch)

• pacinian (pressure)

• krauce (cold)

• ruffini (heat)

hair cycle

• anagen

• catagen

• telogen

anagen

growing phase

catagen

transitory phase between growing and resting phase

telogen

resting phase of hair cycle

function of skin

• barrier - by limiting water and nutrient loss

• temperature regualation - through sweating

• sensory perception - through nerve ending responsible for reacting to touch, pressure, hot and cold

• blood pressure control - through vasoconstriction or vasodilation of arterioles on it

• secretion of sebum and excretion of sweat

• flexibility - buy the aid of connective tissues

• synthesis - vitamin D ‘ calciferol synthesis under influence of sunlight

• storage of nutrient

• immune function - by the aid of skin substances with natural antibacterial and antifungal properties

• pigmentation - melanin secretion by melanocyte for skin protection against ultraviolet radiation

factors affecting the conditon/health of skin

• exogenous

• endogenous

exogenous

physical, chemical, nutritional, infectious, actiric (chemical charges due to radiation)

endogenous

age, heredity, congenital, metabolic, hormonal, immunologic, emotional

PRIMARY LESIONS

are the initial, direct result of a disease process or injury on the skin

PRIMARY LESIONS

• macule

A circumscribed flat area of color change <1cm diameter.

PRIMARY LESIONS

• PATCH

A circumscribed flat area 2of color change >1cm diameter.

PRIMARY LESIONS

• WHEAL

A sharply circumscribed raised lesion consisting of edema.

PRIMARY LESIONS

• papule

A small, solid, raised skin lesion less than 1 cm in diameter

PRIMARY LESIONS

• plaque

A flat-topped, solid elevation in the skin, greater than 1 cm in diameter, often formed by the coalescence of papules.

PRIMARY LESIONS

• nodule

Elevated lesion more than 5 mm size with substantial depth

PRIMARY LESIONS

• cyst

Basically a nodule containing expressible material (usually a clear fluid).

PRIMARY LESIONS

• vesicle and bullae

Vesicles and bullae are both blisters on the skin. However, bullae are larger than

vesicles

PRIMARY LESIONS

• pustule

A small, elevated, pus-filled lesion on the skin, commonly seen in conditions like superficial pyoderma and pemphigus foliaceus in animals.

PRIMARY LESIONS

• petechiae

Are tiny, pinpoint red or purple spots on the skin or mucous membranes, like the gums, caused by small blood vessels bleeding under the skin.

PRIMARY LESIONS

• purpura

• are larger areas of hemorrhage that may be palpable.

• does not blanch.

• Palpable purpura is considered the hallmark of leukocytoclastic vasculitis.

Secondary lesion

develop from changes in primary lesions, either due to progression, infection, scratching, or healings.

SECONDARY LESIONS

• scale

Accumulation of loose, flaky keratin (stratum corneum) on the skin surface; often seen in dry or inflammatory skin conditions.

SECONDARY LESIONS

• comedo

A plug of keratin and sebum within the hair follicle, commonly referred to as a "blackhead" or "whitehead."

SECONDARY LESIONS

• crust

Dried exudate (serum, blood, pus) on the skin surface; also known as a “scab”.

SECONDARY LESIONS

• epidermal colarette

A circular rim of scale that represents the remnants of a ruptured pustule or vesic

SECONDARY LESIONS

• excoriation

Superficial abrasion or scratch mark caused by self-trauma (e.g., from itching).

SECONDARY LESIONS

• fissure

Linear, often painful breaks within the skin surface, as a result of excessive xerosis (dryness of skin).

SECONDARY LESIONS

• erosion

Intraepithelial loss of epidermis, usually heals without scarring, moist, circumscribed, usually depressed lesion due to loss of all or part of the epidermis e.g. herpes simplex.

SECONDARY LESIONS

• ulceration

Full-thickness loss of the epidermis

with damage into the dermis, heals with scarring (e.g. ulcerated hemangiomas, aplasia cutis congenita).

SECONDARY LESIONS

• scar

Permanent fibrotic skin changes that develop as a consequence of tissue injury in which normal tissue is replaced by fibrous connective tissue at the site of injury to the dermis. Scars may be hypertrophic, atrophic, sclerotic or hard due to collagen proliferation. Reflects pattern of healing in the affected area.

SECONDARY LESIONS

• sclerosis

Hardening or thickening of the skin due to chronic inflammation or fibrosis.

SECONDARY LESIONS

• induration

Localized hardening of soft tissue, often due to inflammation, infection, or infiltration.

SECONDARY LESIONS

• lechinefication

Thickening of the skin with accentuation of the skin surface architecture, namely lines and folds.

SECONDARY LESIONS

• hyperpigmentation

Results from increases in rate of production, size, maturation melanosomes or in numbers of melanocytes.

PATHOLOGIC DISRODERS OF SKIN

• keratosis

A condition characterized by the overgrowth of keratin on the skin, leading to thickened areas.

PATHOLOGIC DISRODERS OF SKIN

• hyperkeratosis

Thickening of the outermost layer of the skin (stratum corneum) due to excessive keratin accumulation.

PATHOLOGIC DISRODERS OF SKIN

• orthokeratosis

A form of hyperkeratosis where the stratum corneum is thickened without retained nuclei in the keratinocytes, indicating normal maturation.

PATHOLOGIC DISRODERS OF SKIN

• parakeratosis

A condition where there is retention of nuclei in the stratum corneum, often associated with rapid skin turnover or chronic inflammation.

PATHOLOGIC DISRODERS OF SKIN

• acanthosis nigricans

Characterized by hyperpigmented, thickened, and often velvety skin, primarily affecting areas such as the axillae, groin, and perineum.

PATHOLOGIC DISRODERS OF SKIN

• epitheliogenesis imperfecta

Incomplete formation of skin

PATHOLOGIC DISRODERS OF SKIN

• hypertrichosis

Excessive growth of hair on the extremities, the head, and the back

PATHOLOGIC DISRODERS OF SKIN

• ichthyosis

Congenital skin disorder in which the skin is thickened by scales (hyperkeratosis) that in severe forms can crack into plates resembling fish scales

PATHOLOGIC DISRODERS OF SKIN

• solar dematosis

Skin damage caused by chronic sun exposure, commonly seen in lightly pigmented or sparsely haired animals.

PATHOLOGIC DISRODERS OF SKIN

• callus

Thickened, hairless skin usually over pressure points, such as the elbows in large dogs.intert

PATHOLOGIC DISRODERS OF SKIN

• intertrigo

Inflammation in skin folds due to moisture, friction, and secondary bacterial or yeast infection.

PATHOLOGIC DISRODERS OF SKIN

• folliculitis

Inflammation or infection of hair follicles, often presenting as pustules or papules; common in bacterial skin infections.

PATHOLOGIC DISRODERS OF SKIN

• perifolliculitis

Inflammation of the skin surrounding hair follicles, often accompanying folliculitis (inflammation of the follicles themselves). It can be caused by infections, physical irritation, or other factors. In some cases, like dissecting cellulitis of the scalp, it can lead to scarring and permanent alopecia.

PATHOLOGIC DISRODERS OF SKIN

• furunculosis

• Often called interdigital furunculosis, is a deep bacterial infection of the skin and hair follicles that can lead to painful boils, abscesses, and even draining tracts.

• These lesions, known as furuncles, can appear anywhere on the body but are commonly found between the toes (interdigital) or on the back and neck.

PATHOLOGIC DISRODERS OF SKIN

• paronychia

Inflammation or infection of the skin surrounding the nails or claws, leading to redness, swelling, and pain.

PATHOLOGIC DISRODERS OF SKIN

• seborrhea

A disorder characterized by excessive sebum production, leading to oily or flaky skin.

PATHOLOGIC DISRODERS OF SKIN

• spongiosis

Intercellular edema of the epidermis, typically seen in eczematous dermatitis.

PATHOLOGIC DISRODERS OF SKIN

• erythema

Redness of the skin due to increased blood flow in superficial capillaries, often a sign of inflammation or infection.

PATHOLOGIC DISRODERS OF SKIN

• urticaria/ hives

Raised, red, itchy welts on the skin caused by an allergic reaction or other irritants; due to localized edema in the dermis.

PATHOLOGIC DISRODERS OF SKIN

• wheal and flare reaction

An immediate hypersensitivity reaction marked by a raised, red, itchy area (wheal) surrounded by a flare of redness (flare), commonly seen in allergic responses.

PATHOLOGIC DISRODERS OF SKIN

• alopecia

The partial or complete loss of hair in areas where it is normally present, which can result from various causes including hormonal imbalances, infections, or autoimmune diseases.

agents of parasitic dermatitis

• Sarcoptes scabiei (ITCH MITE)

A mite that causes sarcoptic mange, a highly contagious skin disease in animals and humans. This burrowing mite is transmitted through direct contact and can cause intense itching, skin lesions, and discomfort.

Demodex canis (DOG FOLLICLE MITE)

A parasitic mite that causes demodectic mange, also known as red mange, in dogs. It is a common skin condition where the mites live in the dog's hair follicles.

Sarcoptes scabiei (ITCH MITE)

A severe case of S. scabiei infestation in a stray cat from Italy, characterized by bilateral alopecia, diffuse and multifocal hyperpigmented, crusted, erythematous, scaled, and exfoliated lesions.

Demodex canis (DOG FOLLICLE MITE)

Canine demodicosis is a common inflammatory parasitic skin disease believed to be associated with a genetic or immunologic disorder. This disease allows mites from the normal cutaneous biota to proliferate in the hair follicles and sebaceous glands, leading to alopecia, erythema, scaling, hair casting, pustules, furunculosis, and secondary infections.

Notoedres cati (FELINE SCABIES)

A mite that causes notoedric mange in cats, leading to intense pruritus, crusting, and hair loss, especially on the ears and face.

Otodectes cynotis (EAR MITES)

responsible for otitis externa in cats and dogs; causes intense ear irritation and a dark, waxy discharge.

Notoedrescati (FELINESCABIES)

Initial lesions are usually around the ears and face and are characterised by intense pruritus and a dry, crusty appearance. Notoedres is similar to Sarcoptes in appearance and clinical presentation.

Otodectes cynotis (EAR MITES)

Very contagious by direct contact or through fomites such as bedding or grooming equipment. Ear mite infestation can spread rapidly in a group of dogs or cats, especially if the hosts are young, immunosuppressed or are in other ways stressed.

Ctenocephalides spp. (Cat and Dog fleas)

Are fleas, small wingless ectoparasitic insects that commonly infest domestic dogs and cats.

The two main species are:

• Ctenocephalides felis (cat flea) — the most common flea on both cats and dogs worldwide

• Ctenocephalides canis (dog flea) — less common, mainly found on dogs

Cheyletiella spp. (Walking Dandruff)

Are mites known as “walking dandruff” because of the visible dandruff-like flakes they produce on infested animals. They are highly contagious ectoparasites primarily of dogs, cats, and rabbits.

Ctenocephalides spp. (Cat and Dog fleas)

Common ectoparasites of dogs and cats, especially Ctenocephalides felis (cat flea) and Ctenocephalides canis (dog flea). They are blood-feeding parasites that cause itching, flea allergy dermatitis, and can transmit diseases and parasites. Flea infestations spread by direct contact or through infested environments such as bedding or grooming tools.

Cheyletiella spp. (Walking Dandruff)

Are mites known as “walking dandruff” because of the visible dandruff-like flakes they produce on infested animals. They are highly contagious ectoparasites primarily of dogs, cats, and rabbits.

Argas persicus (FOWL TICK)

A soft-bodied tick that primarily infests poultry, hiding in crevices during the day and feeding on birds at night. It can transmit diseases like avian spirochetosis.

Rhipicephalus sanguineus (Brown Dog Tick)

A hard-bodied tick that predominantly feeds on dogs and can transmit various pathogens, including those causing canine ehrlichiosis and babesiosis.

Argas persicus (Fowl Tick)

Also known as the poultry tick, it primarily affects birds like chickens. It hides in cracks during the day and feeds at night, causing irritation, weight loss, decreased egg production, and even anemia in severe infestations. It can also transmit diseases like avian spirochetosis.

Rhipicephalus sanguineus (Brown Dog Tick)

This tick mainly targets dogs but can also bite humans. It thrives in warm environments, including homes and kennels. It causes skin irritation, anemia, and can transmit serious diseases like Ehrlichiosis and Babesiosis in dogs.

Dermanyssus gallinae (POULTRY RED MITE)

Is a small blood-feeding mite that infests poultry

Ancylostoma caninum

Is a hookworm in dogs causing anemia. Infection via skin or ingestion. Prevent with deworming.

general cauases of parasitic dermatitis’

• insect bites (lice and fleas)

• acarid bites (ticks and mites)

• burrowing activities of mites

• migrating stages of parasite

major effects of skin parasites

• acute or chronic inflammation

• acitivation of inflammatory cells

• acute phase: neutrophil and eosinophil

• chronic phase: plasma cell, macrophage, and proliferating fibroblast

• stylostome - sucking tubes of chiggers

parasite that causes dermatiti

• protozoan - Globidia spp. (besnoitia)

• simuliasis - simulium (blackflies)

• hypodermyiasis - hypoderma bovis and H. lineatum (larva)

• gasterophilomyiasis - gasterophillus (larva in mouthparts of horse)

• trombiculiasis - trombicula mites (chiggers”larva mites)

• gamasoidiasis - dermanyssus gallinae, ornithonyssus sylviarum and o. bursa

• trematodiasis - schistosome metacercariae (causing cercarial dermatitis)

• collyricium - (causing subcutaneous cyst in fowl)

• nematodiasis - habronemiasis (summer sore) strongyloides stercoralis and rhabditis strongyloides (causes papular and pustular dermatitis

• microfiliariasis - onchocerca, parafilaria, dirofilaria (in tropics and warmer regions there us dermatitis and skin ulceration)

• elaeophoriasis - E,aephora schneideri (microfilaria also causes dermatitis) creeping eruption in human -Ancylostoma spp

neoplastic disorders of skin

• benign

• malignant

benign

marked by disorganization of the granular layers of the epidermis, swollen and eosinophilic cytoplasm, and sometimes viral particles if poxvirus

malignant

hyperchromatism (with darker color of cells) increased mitotic activity, enlargement of cell nuclei and can lead to carcinoma