Integumentary System Quiz

Integumentary System: VPM 3419

• The Integumentary system is the largest body system, forming an anatomical boundary between the animal and its environment.
• Skin diseases are common in veterinary practice and can indicate systemic diseases, causing significant economic losses in food animals and zoonotic transmission.
• Functions:
  • Protection: Protects against ultraviolet light, mechanical, chemical, and thermal insults, acting as a barrier against water loss, electrolyte loss, macromolecules and micro-organism invasion.
  • Sensation: Contains receptors for touch, pressure, pain, and temperature.
  • Thermoregulation: Hairs and subcutaneous adipose tissue insulate the body against heat loss. Excess heat is evaporated through sweat and increased blood flow in the skin.
  • Metabolic: Subcutaneous adipose tissue is a major energy store (triglycerides). Epidermis synthesizes Vitamin D.
  • Motion, Shape, and Colour: Skin's flexibility, elasticity, and toughness allow movement and define shape and form. Processes in skin (melanin formation, vascularity, keratinization) influence coat and skin colour. Pigmentation prevents damage from solar radiation.
  • Indicators: Skin can be a valuable indicator of internal diseases.

Skin Structure

• Composed of epidermis, dermis, hair follicles, adnexal glands, and subcutis.
• The structure shows layered features in different images of the skin.

Epidermis, Dermis and Hypodermis

• Epidermis:
  • Stratum basale (basal layer): single layer of cuboidal/columnar cells; mitosis is often limited.
  • Stratum spinosum (prickle layer): several layers of polygonal cells
  • Stratum granulosum (granular layer): one or more layers of nucleated, flattened keratinocytes.
  • Stratum lucidum (clear layer): thin layer of flattened, unstained cells (found in paw and nose).
  • Stratum corneum (horny layer): multiple layers of dead, fully keratinized, flattened cells.
• Epidermal Appendages (Adnexa):
  • Hair Follicles: simple (e.g., cattle, horses) and compound (e.g., sheep, dogs, cats). Hair follicles have cyclical growth (anagen, catagen, telogen). Hair follicles possess multiple components: shaft, bulb, papilla, internal root sheath, external root sheath, sebaceous gland, arrector pili muscle and apocrine sweat glands.
  • Glands:
    • Sebaceous glands: part of hair follicle complex, secrete sebum (triglycerides + cholesterol).
    • Apocrine sweat glands: develop as part of hair follicle complex, opening into hair follicles; effective in hoofed animals.
    • Eccrine sweat glands: not associated with hair follicles; effective in mammals without hooves. Secrete water and salt.
• Dermis (Corium):
  • Support and nourish epidermis and appendages.
  • Composed of collagen, reticulin, and elastin fibers embedded in ground substance.
  • Contains fibroblasts, mast cells, lymphocytes, macrophages (few) also eosinophils & neutrophils.
  • Has superficial and deep layers of different fiber density.
• Hypodermis (Subcutis):
  • Heat insulator, contributing to body shape.
  • Composed of lipocytes, blood vessels, nerves, and connective tissue.
  • Cutaneous vasculature (superficial, middle, deep). Nerve fibers follow blood vessels, lymphatics in superficial dermis.

Dermal Histopathology

• Hyperkeratosis: thickened stratum corneum (absolute or relative). May be orthokeratotic or parakeratotic, focal or generalized.
• Hypokeratosis: decreased stratum corneum thickness
• Dyskeratosis: premature and faulty keratinization of viable cells in stratum spinosum
• Hyperplasia/Acanthosis: increased epidermis thickness related to cell number in non-cornified epidermis
• Hypoplasia/ Atrophy: reduced epidermis thickness related to decreased cell number or size of non-cornified epidermis
• Necrosis/Necrolysis: death of cells or tissues; nuclear changes, loss of intercellular bridges, eosinophilia of cytoplasm
• Intercellular Oedema (Spongiosis): widening of epidermis intercellular bridges (common in acute/subacute dermatosis)
• Intracellular Oedema: increased cell size and cytoplasmic pallor (often from viral infection or artifacts, resembling freezing or improper fixation)
• Ballooning Degeneration: swollen, eosinophilic cytoplasm/cells without vacuoles: common in viral infections
• Hydrophic Degeneration: Intracellular oedema in the stratum basale; often associated with Lupus erythematosus or drug reactions
• Acantholysis: loss of cohesion between epidermal cells; causing clefts, vesicles, and bullae (common in severe spongiosis or viral infection); may be caused by proteolytic enzymes
• Exocytosis: migration of inflammatory cells into epidermis.
• Clefts (lacunae): slit-like spaces without fluid
• Microvesicles, vesicles, bullae: small to large fluid-filled spaces in or below the epidermis.
• Microabscesses/Pustules: intraepidermal and subepidermal cavities containing inflammatory cells
• Hyperpigmentation (hypermelanosis): increase/excess melanin in epidermis
• Hypopigmentation (hypomelanosis): decrease in melanin deposition in epidermis
• Crusts: consolidated, desiccated serum, keratin debris, and microbes. Can be serous, hemorrhagic, or cellular/seocellular. Crust may be various colours.
• Horn cysts (keratin cysts): circular cysts surrounded by flattened epidermal cells with keratin layers.
• Horn pearls (squamous pearls): focal circular structures of concentric keratin layers in the centre, often with dyskeratosis; often associated with squamous cell carcinoma.

Dermal Changes

• Dermal collagen: collagen hyalinization with confluence; characterized by increased eosinophilia, glassy refractile appearance (often in chronic inflammation)
• Fibrinoid degeneration: brightly eosinophilic fibrillar/granular substance resembling fibrin; indicative of connective tissue disease.
• Fibrosis, Fibroplasia, Sclerosis: increase in fibrous tissue (e.g., granulation tissue), prominent fibroblast cells, and increased collagen fibrils (often with inflammation) ; sclerosis is a later stage of the process.
• Exuberant Granulation Tissue: vertically and horizontally oriented capillaries and few collagen fibres.
• Papillomatosis: projection of dermal papillae above skin surface, often with epidermal hyperplasia.
• Pigmentary incontinence: presence of melanin granules free in subepidermal dermis and within dermal macrophages (melanophages).
• Dermal oedema: widened perivascular interstitial spaces.
• Mucinous degeneration: increase in amorphous, stringy, granular materials displacing collagen fibrils.
• Follicular epithelium: Follicular keratosis, plugging and dilatation or atrophy of follicles, resulting from hormonal disease.
• Sebaceous glands/apocrine, sweat glands: suppurative or granulomatous inflammations, atrophy, cysts, hyperplasia (related to chronic inflammation or hormonal disease).
• Cutaneous blood Vessels: dilation, endothelial swelling, vasculitis or thromboembolism.

Subcutaneous Changes

• Suppurative and granulomatous dermatoses.
• Inflammatory changes (e.g., panniculitis, steatitis).
• Necrosis.

Test your knowledge about the integumentary system and the functions of the epidermis. This quiz covers various aspects including skin structure, functions, and the role of hair follicles. Perfect for students studying anatomy or related fields.