Integument Microanatomy- Pt 1

Integument: General Info

• Collagen dysplasia is an example of an integumental disease.
• Integument is the composition of skin and epidermal derivatives.
• Epidermal derivatives include: foot pads, claws, horns, hooves, glands (like anal sacs), uropygial glands, wattles, combs, spurs, and feathers.

Skin: General Info

• Skin is the largest organ in the body, composing 8-16% of body weight.
• Skin functions include: protection, prevent water and electrolyte loss, calcium homeostasis, temperature regulation, sensation, energy storage, and immune functions.

Skin Types

• Thick skin: hairless, thick epidermis layer, merocrine/eccrine sweat glands. Examples: paw pads and muzzles.
• Thin skin: hair follicles (often with arrector pili muscles), thin epidermis layer, sebaceous glands, and apocrine sweat glands.

Skin: Composition

• Skin is composed of the epidermal layer, dermal layer, and hypodermal layer.
• Dermal layer can be further subdivided into the papillary layer (loose connective tissue) and reticular layer (dense irregular connective tissue).

Epidermis

• Epidermis is an avascular, thick barrier of epithelium composed of stratified keratinized epithelium.
• Keratinocytes compose 95% of cells in the epidermal layer.
• Non-keratinocytes found in the epidermis include: Langerhans cells (immune function as a tissue macrophage), Merkel's cells (mechanoreceptors), and melanocytes (UV protection).

Dermis

• Dermis is composed of blood vessels, connective tissue, and nervous tissue.
• Dermis functions to support the epidermis.
• Things found in the dermal layer include: blood vessels, collagen fibers, elastic fibers, resident cells, transient cells, nerves, and lymphatics.

Hypodermis (Subcutis)

• Hypodermis contains panniculus adiposus, which is loose connective tissue that's rich in adipocytes.
• Hypodermal layer is located beneath the dermis.

Dermo-Epidermal Junction

• Dermo-epidermal junction is the interface between the dermis and epidermis.
• Examples of where dermo-epidermal junctions can be found include: footpads, nasal planum, scrotum, and areas subjected to traction.

Epidermal Pegs/Ridges and Dermal Papilla

• Epidermal pegs/ridges: downward projections of the deep epidermis into the dermis.
• Dermal papilla: upward projections of superficial dermis that bring blood supply closer to the epithelium.

Epidermis: Layers

• Stratum basale: active, alive, cuboidal to columnar epithelium, keratinocytes, and melanocytes.
• Stratum spinosum: active, alive, polygonal, cohesive, and resistant to abrasion.
• Stratum granulosum: alive, but non-active, contains basophilic keratohyalin granules, and lamellar granules.
• Stratum lucidum: not always present, deceased, translucent, and contains desmosome, many keratin filaments, and cytoplasm with eleidin.
• Stratum corneum: deceased, outermost epidermal layer, contains up to 20 cell layers, lacks nuclei and organelles, and consists entirely of keratin.