Integumentary System Vocabulary

Flashcards covering the vocabulary and key concepts of Unit D: Integumentary System, including skin layers, cell types, accessory structures, functions, and clinical pathologies.

Integument

The body's largest organ, comprising approximately $8\%$ of total body weight, composed of epithelial, connective, smooth muscle, and nervous tissue.

Epidermal Dendritic Cells

Immune cells located in the stratum spinosum and stratum granulosum that initiate immune responses against pathogens and epidermal cancer cells.

Calcitriol

The active hormonal form of vitamin D converted in the kidneys from calcidiol, which increases intestinal absorption of calcium and phosphate.

Vasoconstriction

The narrowing of dermal blood vessels to shunt blood away from the body periphery toward deeper structures in order to conserve heat.

Vasodilation

The widening of dermal blood vessels allowing increased blood flow close to the skin surface to dissipate heat.

Subcutaneous Layer

Also called the hypodermis; a layer deep to the dermis composed of areolar and adipose connective tissue that pads the body and stores energy, but is not part of the integumentary system.

Regeneration

A tissue repair mechanism where damaged or dead cells are replaced with the same cell type, restoring full organ function.

Fibrosis

A tissue repair mechanism where a wound gap is filled with scar tissue composed of collagen produced by fibroblasts, failing to restore functional activity.

Rule of Nines

A clinical tool used to estimate the surface area involvement of burns by dividing the body into regions assigned percentage values in multiples of nine.

First-Degree Burn

A burn involving only the epidermis, characterized by slight redness and pain.

Second-Degree Burn

A burn involving the epidermis and part of the dermis, characterized by skin blistering, pain, and slight scarring.

Third-Degree Burn

A severe burn involving the epidermis, dermis, and subcutaneous layer, requiring hospitalization to treat dehydration, swelling, and risk of infection.

Epidermal Strata

The distinct cell layers of keratinized stratified squamous epithelium in thick skin, ordered from deep to superficial: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.

Keratinocytes

The most abundant cell type in the epidermis, present across all strata, responsible for synthesizing keratin to strengthen and waterproof the skin.

Melanocytes

Pigment-producing cells in the stratum basale that synthesize melanin and transfer melanosomes into keratinocytes to shield nuclear DNA from UV radiation.

Merkel (Tactile) Cells

Specialized sensory cells scattered within the stratum basale that release chemicals upon compression to stimulate sensory nerve endings.

Keratinization

A process beginning in the stratum granulosum where keratinocytes fill with keratin, causing their nucleus and organelles to disintegrate.

Stratum Lucidum

A translucent, clear layer of 2 to 3 dead cell layers found exclusively in thick skin on the palms and soles, containing the protein eleidin.

Stratum Corneum

The most superficial epidermal layer consisting of 20 to 30 layers of dead, anucleate, interlocking keratinized cells.

Thick Skin

Epidermis measuring $0.4\text{ mm to }0.6\text{ mm}$ thick found on palms and soles containing all five strata and sweat glands, but lacking hair follicles and sebaceous glands.

Thin Skin

Epidermis measuring $0.075\text{ mm to }0.150\text{ mm}$ thick covering most of the body, lacking a stratum lucidum, but containing sweat glands, hair follicles, and sebaceous glands.

Carotene

A yellow-orange pigment acquired from vegetables that accumulates in subcutaneous fat and stratum corneum keratinocytes, serving as a precursor to vitamin A.

Albinism

An inherited recessive condition in which the enzyme needed to produce melanin is nonfunctional, leaving melanocytes unable to synthesize pigment.

Nevus

A harmless, localized overgrowth of melanocytes, commonly referred to as a mole.

Hemangioma

A benign blood vessel tumor present as red to purple skin lesions, categorized as capillary (strawberry birthmarks) or cavernous (port-wine stains).

Friction Ridges

Large folds and valleys of the dermis and epidermis forming unique patterns of arches and whorls on fingers, palms, soles, and toes.

Papillary Layer

The superficial region of the dermis composed of areolar connective tissue with dermal papillae that interdigitate with epidermal ridges.

Reticular Layer

The deeper, major portion of the dermis composed of dense irregular connective tissue containing large, interwoven collagen fiber bundles.

Cleavage Lines

Parallel orientations of collagen and elastic fiber bundles in the dermis that resist stress; incisions parallel to them heal faster with reduced gaping.

Eponychium

The narrow band of stratum corneum extending over the proximal edge of the nail body, commonly called the cuticle.

Lanugo

Fine, unpigmented, downy hair appearing on the fetus during the last trimester of development.

Vellus

Fine, unpigmented primary hair covering most upper and lower limbs.

Terminal Hair

Coarser, pigmented, longer hair found on the scalp, eyebrows, eyelashes, and pubic/axillary regions post-puberty.

Hair Bulb

The swelling at the base where hair originates in the dermis, containing living epithelial cells and the hair matrix.

Anagen Phase

The active growth phase of the hair cycle where live matrix cells rapidly divide, lasting $18\text{ months to }7\text{ years}$.

Catagen Phase

A brief regression phase of the hair cycle lasting $3\text{ to }4\text{ weeks}$ where cell division in the follicle ceases.

Telogen Phase

The resting phase of the hair cycle lasting $3\text{ to }4\text{ months}$ during which the hair is shed.

Alopecia

A general term for hair loss or thinning due to aging, hormonal changes, or systemic disease.

Hirsutism

Excessive male-pattern hairiness on areas like the face, chest, and back caused by excess androgens.

Merocrine Sweat Glands

Simple coiled tubular exocrine glands distributed widely across the body that secrete watery sweat for thermoregulation via fluid evaporation.

Apocrine Sweat Glands

Coiled tubular glands discharging viscous, cloudy secretions into hair follicles in axillary, pubic, and nipple regions that become active during puberty.

Sebaceous Glands

Holocrine glands that secrete oily sebum into hair follicles to lubricate skin and hair.

Ceruminous Glands

Modified apocrine sweat glands located in the external ear canal that secrete waterproof earwax (cerumen).

Psoriasis

A chronic autoimmune skin disease where T-lymphocytes attack keratinocytes, resulting in rapid skin cell overgrowth and silvery scaly patches.

Decubitus Ulcer

A chronic open skin wound or pressure sore caused by continuous restriction of blood supply to a tissue region.