Integument: Structure and Function

Comprehensive vocabulary flashcards covering the structural layers, cellular differentiation, pigmentation, tissue repair, accessory glands, thermal homeostasis, and calcium synthesis of the integumentary system based on Lecture 4.

Integument

The largest and most visible organ of the body, composed of the cutaneous membrane (epidermis and dermis) along with accessory structures.

Cutaneous Membrane

The biological skin itself, consisting of two primary structural layers: the superficial epithelial epidermis and the underlying connective tissue dermis.

Epidermis

The superficial, avascular layer of the cutaneous membrane made of a stratified squamous epithelium divided into distinct cellular strata.

Dermis

The vascularized connective tissue layer beneath the epidermis that supports accessory structures and consists of two layers: the stratum papillare and stratum reticulare.

Hypodermis (Subcutis)

The layer of subcutaneous fat and connective tissue situated beneath the dermis; it is functionally associated with skin but is not considered an anatomical part of the integument.

Thick Skin

Hairless skin located exclusively on the palmar and plantar surfaces, featuring five epidermal strata (including the stratum lucidum) and a prominent stratum corneum.

Thin Skin

Hairy skin that covers the majority of the body surface, characterized by an epidermis with four strata (lacking the stratum lucidum) and containing hair follicles and sebaceous glands.

Stratum Basale

The deepest epidermal layer where basal cells undergo active proliferation and renewal, and where melanocytes reside attached to the basement membrane.

Stratum Spinosum

The epidermal layer situated directly superficial to the stratum basale where differentiating keratinocytes form spiny desmosomal connections.

Stratum Granulosum

The epidermal layer where keratinocytes accumulate protein granules, become heavily keratinized, and begin losing their cellular nuclei and organelles.

Stratum Lucidum

A clear, glassy band of flattened, dead keratinocytes found exclusively in the thick skin of palms and soles between the stratum granulosum and stratum corneum.

Stratum Corneum

The most superficial layer of the epidermis, composed of multiple flattened layers of dead, fully keratinized cells that are continuously shed and replaced.

Keratin

A tough, cross-linked, water-resistant intermediate filament protein accumulated by epidermal keratinocytes that limits water loss and provides mechanical resistance.

Insensible Perspiration

The passive loss of interstitial water by direct evaporation through the cutaneous membrane itself, occurring independently of active sweat gland secretion.

Melanocyte

A specialized pigment-producing cell in the stratum basale that synthesizes melanin and packages it into transport vesicles called melanosomes.

Melanosome

A membrane-bound pigment vesicle produced by melanocytes that is transferred via vesicle transport into adjacent keratinocytes to shield nuclear DNA from UV photons.

Melanin

A cellular pigment that protects epidermal DNA by absorbing ultraviolet (UV) photons and harmlessly releasing the absorbed radiation energy as heat.

Eumelanin

A predominant class of melanin pigment that produces brown and black tones, providing high photoprotection against UV-induced damage.

Pheomelanin

A sulfur-containing variant of melanin pigment that produces reddish-to-yellow hues with lower efficacy at protecting DNA against UV radiation.

Callus

A localized thickening of the stratum corneum formed when repetitive mechanical stress or friction causes keratinocytes to become more strongly cross-linked, delaying cellular shedding.

Blister (Vesicle)

A fluid-filled epidermal separation caused by shearing forces pulling layers apart—typically separating the stratum granulosum from the stratum spinosum—allowing interstitial fluid to accumulate.

Stratum Papillare

The superficial dermal layer composed of loose areolar connective tissue proper that interlocks with epidermal ridges, housing capillary loops and sensory nerve fibers.

Stratum Reticulare

The deeper, thicker dermal layer composed of dense irregular, elastic connective tissue that contains extensive vasculature and sensory receptor networks.

Granulation Tissue

A delicate, highly vascularized repair tissue formed in the dermis during the migratory phase, composed of a mixture of newly sprouted capillary loops, mesenchymal cells, and fibroblasts.

Scar Tissue

Fibrous dermal repair tissue generated when activated fibroblasts deposit dense collagen fibers and ground substance to bridge a deep wound.

Keloid

An exaggerated, raised fibrous growth that extends beyond the boundaries of an original injury, caused by persistent hyperproliferation and excessive collagen secretion by dermal fibroblasts.

Sebaceous Gland

An exocrine gland associated with hair follicles that discharges an oily lipid secretion (sebum) to coat, lubricate, and waterproof the surrounding epidermis and hair shaft.

Apocrine Sweat Gland

A coiled tubular exocrine gland confined primarily to the axillary and pubic regions that secretes a viscous product into hair follicles.

Eccrine Sweat Gland

A widely distributed exocrine gland that secretes watery sweat directly onto the surface of the epidermis to facilitate evaporative cooling during thermal homeostasis.

Cutaneous Vasodilation

The widening of blood vessels in the superficial dermis, increasing blood flow to the skin surface to disperse heat into the environment via radiation and convection.

Cutaneous Vasoconstriction

The narrowing of blood vessels supplying the superficial dermis, diverting blood flow toward deep visceral tissues to retain body heat in cold conditions.

Erythema

Visible superficial skin redness caused by increased blood flow through dilated dermal capillaries, commonly seen after exercise, heat exposure, or alcohol consumption.

Cholecalciferol (Vitamin $\text{D}_3$)

A steroid precursor synthesized in the epidermis when epidermal cells absorb specific ultraviolet (UV) wavelengths, which is later modified into calcitriol.

Calcitriol

An active steroid hormone synthesized sequentially by the liver and kidneys from cholecalciferol, required for the intestinal absorption of dietary calcium ($\text{Ca}^{2+}$).

Photoaging

Premature, accelerated aging and structural breakdown of the integument—manifesting as deep wrinkling and loss of dermal elasticity—caused by cumulative absorption of solar UV radiation.

Volar Fibroblasts

Specialized dermal fibroblasts derived from the sole or palm that, upon transplantation into nonvolar skin, instruct local epithelial cells to produce thick-skin traits including elevated keratin 9 ($KRT9$).