Integumentary System

Cards · 55

Integumentary System

Organ system consisting of skin, hair, nails, and exocrine glands that protects the body and maintains homeostasis.

Epidermis

Avascular, outermost layer of the skin composed of keratinized stratified squamous epithelium.

Dermis

Vascular, middle layer of the skin composed of dense irregular and loose areolar connective tissue.

Hypodermis (Subcutaneous layer)

Deepest layer beneath the dermis, composed mostly of adipose and loose areolar connective tissue; anchors skin to underlying muscle.

Stratum Basale

Deepest epidermal layer, consisting of a single row of actively dividing stem cells attached to the basement membrane.

Stratum Spinosum

Epidermal layer above stratum basale containing spiny-appearing keratinocytes held together by desmosomes and containing Langerhans cells.

Stratum Granulosum

Layer of 3 to 5 cell layers where keratinocytes flatten, lose nuclei, and accumulate keratohyalin and lamellar granules.

Stratum Lucidum

Clear, translucent band of dead keratinocytes found only in thick skin like the palms and soles.

Stratum Corneum

Outermost epidermal layer consisting of 20 to 30 layers of dead, flattened, anucleate, fully keratinized corneocytes.

Keratinocytes

Predominant epidermal cells (about 90%) that produce keratin, a tough fibrous protein providing structural protection.

Melanocytes

Pigment-producing cells in the stratum basale that synthesize melanin and transfer it to keratinocytes to protect DNA from UV damage.

Langerhans Cells (Dendritic Cells)

Immune cells located primarily in the stratum spinosum that act as antigen-presenting cells against skin pathogens.

Merkel Cells (Tactile Cells)

Sensory cells located in the stratum basale that combine with disc-like sensory nerve endings to detect light touch.

Thick Skin

Skin found on palms and soles containing all five epidermal strata, lacking hair follicles and sebaceous glands.

Thin Skin

Skin covering most of the body containing four epidermal strata (lacking stratum lucidum) and harboring hair follicles and glands.

Papillary Dermis

Superficial dermal layer composed of loose areolar connective tissue containing dermal papillae, capillary loops, and Meissner's corpuscles.

Reticular Dermis

Deeper, thicker dermal layer composed of dense irregular connective tissue rich in collagen and elastin fibers.

Dermal Papillae

Peg-like projections of the papillary dermis into the epidermis that increase surface area for adhesion and form epidermal ridges (fingerprints).

Fibroblasts

Primary cells of the dermis responsible for synthesizing collagen, elastin fibers, and extracellular ground substance.

Mast Cells

Dermal immune cells that release histamine, heparin, and other inflammatory mediators during injury or allergic response.

Adipocytes

Fat-storing cells predominating in the hypodermis, providing thermal insulation, energy storage, and mechanical cushioning.

Collagen Fibers

Tough, flexible protein fibers in the dermis providing tensile strength to resist pulling forces and prevent tearing.

Elastic Fibers

Coiled protein fibers composed of elastin that grant the dermis stretchability and elasticity, returning skin to rest.

Meissner's Corpuscles (Tactile Corpuscles)

Encapsulated nerve endings in dermal papillae responsible for detecting light touch, low-frequency vibrations, and texture changes.

Pacinian Corpuscles (Lamellar Corpuscles)

Large, encapsulated mechanoreceptors located deep in the reticular dermis and hypodermis that detect deep pressure and high-frequency vibration.

Ruffini Endings (Bulbous Corpuscles)

Mechanoreceptors in the reticular dermis sensitive to skin stretch, continuous pressure, and joint movement.

Free Nerve Endings

Unencapsulated sensory receptors throughout the epidermis and dermis sensitive to pain (nociception), temperature, and itching.

Eccrine Sweat Glands (Merocrine)

Coiled tubular glands distributed widely across the body that secrete a hypotonic, watery solution directly onto the skin for thermoregulation.

Apocrine Sweat Glands

Glands located in axillary and anogenital regions that secrete an odor-producing, protein- and lipid-rich sweat into hair follicles.

Sebaceous Glands

Holocrine glands associated with hair follicles that secrete sebum, an oily substance that lubricates and waterproofs skin and hair.

Ceruminous Glands

Modified apocrine sweat glands in the external ear canal that secrete cerumen (earwax) to trap foreign particles and protect the tympanic membrane.

Mammary Glands

Specialized, modified apocrine glands embedded in subcutaneous tissue that produce milk during lactation.

Hair Follicle

Tubular invagination of the epidermis extending into the dermis from which hair strands grow and develop.

Hair Bulb

Swollen base of the hair follicle containing the actively dividing hair matrix and vascularized dermal papilla.

Hair Matrix

Germinative layer of epithelial cells in the hair bulb that actively divides to generate the hair shaft and internal root sheath.

Hair Shaft

Dead, visible keratinized portion of the hair extending beyond the skin surface, composed of medulla, cortex, and cuticle.

Hair Medulla

Innermost core of the hair shaft composed of large, loosely packed cells and air spaces, typically present in thick hairs.

Hair Cortex

Intermediate layer of the hair shaft composed of elongated keratinized cells containing melanin, providing hair its strength and color.

Hair Cuticle

Outermost layer of the hair shaft made of a single layer of overlapping, heavily keratinized, shingle-like cells.

Arrector Pili Muscle

Bundle of smooth muscle tissue attached to the hair follicle that contracts during cold or fear to pull the hair upright, causing goosebumps.

Nail Plate (Body)

Visible, hard, translucent portion of the nail made of densely compacted, non-living keratinized stratified squamous cells.

Nail Matrix

Thickened epithelial zone at the proximal nail fold where actively dividing cells produce new nail plate cells.

Nail Bed

Layer of epidermis underlying the nail plate, highly vascularized and lacking a stratum granulosum.

Lunula

Whitish, crescent-shaped region at the base of the nail plate where the underlying thick matrix obscures vascular visibility.

Eponychium (Cuticle)

Narrow fold of stratum corneum extending from the proximal nail fold over the base of the nail plate, preventing microbial entry.

Hyponychium

Thickened stratum corneum beneath the free edge of the nail that seals the space between the nail and the fingertip.

Melanin

Pigment produced by melanocytes, synthesized as brown-black eumelanin or reddish-yellow pheomelanin, determining skin and hair tone.

Keratin

Insoluble, tough, fibrous structural protein providing mechanical resistance and water-repellent properties to epidermis, hair, and nails.

Keratohyalin Granules

Intracellular granules in the stratum granulosum containing profilaggrin, which aggregates keratin filaments into tight bundles.

Lamellar Bodies

Lipid-filled organelles within stratum granulosum cells that exocytose glycolipids into intercellular space to form a water barrier.

Desmosomes

Intercellular anchoring junctions that strongly bind adjacent keratinocytes together, conferring high mechanical shear strength.

Basement Membrane (Dermal-Epidermal Junction)

Specialized extracellular matrix composed of lamina lucida, lamina densa, and fibroreticular lamina anchoring epidermis to dermis.

Vitamin D Synthesis

Process where 7-dehydrocholesterol in epidermal cells is converted by UV-B radiation into cholecalciferol (vitamin D3).

Thermoregulation by Vasodilation

Expansion of dermal blood vessels to increase cutaneous blood flow and release body heat into the external environment.

Thermoregulation by Vasoconstriction

Narrowing of dermal blood vessels to divert blood away from the skin toward core organs, conserving metabolic heat.