The Integumentary System

Comprehensive vocabulary flashcards covering the anatomical structures, histological strata, cellular functions, skin appendages, sensory receptors, pigmentary variations, clinical burn assessments, and pathologies of the integumentary system.

Dermatology

The scientific study and medical treatment of the integumentary system.

Epidermis

The outermost, avascular layer of the skin composed of keratinized stratified squamous epithelium that relies on diffusion of nutrients from dermal capillaries.

Dermis

The deeper, vascular connective tissue layer of the skin beneath the epidermis that consists of the papillary and reticular layers and accounts for the bulk of skin thickness.

Hypodermis (Subcutaneous Layer)

The layer of adipose and areolar connective tissue deep to the dermis that binds skin to underlying structures, pads the body, and serves as an energy reservoir and thermal insulator.

Thick Skin

Skin covering the palms and soles that features an epidermis of approximately $0.5\,\text{mm}$, contains five strata (including stratum lucidum) and sweat glands, but lacks hair follicles and sebaceous glands.

Thin Skin

Skin covering most of the body with an epidermis of approximately $0.1\,\text{mm}$, containing four strata (lacking stratum lucidum), hair follicles, sebaceous glands, and sweat glands.

Keratinocytes

The most abundant cell type of the epidermis that synthesizes keratin intermediate filaments, is joined by desmosomes and tight junctions, and has a turnover time of approximately $25$ to $45\,\text{days}$.

Melanocytes

Cells located in the stratum basale that synthesize melanin within melanosomes and transfer pigment granules to keratinocytes to form a protective shield over the nucleus against ultraviolet radiation.

Tactile (Merkel) Cells

Touch receptor cells found in the stratum basale that are intimately associated with an underlying dermal sensory nerve fiber to detect light touch and sustained pressure.

Dendritic (Langerhans) Cells

Antigen-presenting immune macrophages originating in the bone marrow that reside in the stratum spinosum and stratum granulosum to guard against toxins, microbes, and pathogens.

Stratum Basale

The deepest epidermal layer consisting of a single row of cuboidal to low columnar actively mitotic stem cells, melanocytes, and tactile cells attached along a wavy basement membrane.

Stratum Spinosum

Several layers of keratinocytes connected by desmosomes that contain thick bundles of pre-keratin intermediate filaments and scattered dendritic cells.

Stratum Granulosum

One to five layers of flattened keratinocytes containing dark-staining keratohyalin granules and membrane-coating lamellar granules that release water-resistant glycolipids.

Stratum Lucidum

A thin, translucent band of flat, dead, anucleate keratinocytes seen exclusively in the thick skin of the palms, fingertips, and soles.

Stratum Corneum

The superficial horny layer composed of $20$ to $30\,\text{layers}$ of dead, flattened, anucleate keratin sacs surrounded by extracellular glycolipids that resist abrasion, penetration, and water loss.

Desquamation

The continuous shedding of dead, keratinized epidermal flakes from the stratum corneum, totaling approximately $18\,\text{kg}$ over a human lifetime.

Papillary Layer

The superficial zone of the dermis composed of loose areolar connective tissue that forms dermal papillae and houses capillary loops, free nerve endings, and Meissner corpuscles.

Reticular Layer

The deeper, thicker dermal zone comprising approximately $80\%$ of dermal thickness, composed of dense irregular connective tissue with prominent collagen bundles, elastic fibers, and Pacinian corpuscles.

Meissner (Tactile) Corpuscles

Rapidly adapting sensory receptors situated in the dermal papillae of hairless skin that detect light touch and low-frequency vibrations.

Pacinian (Lamellar) Corpuscles

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

Free Nerve Endings

Unencapsulated sensory dendrites extending into the upper dermis and epidermis that function as thermoreceptors and nociceptors to register temperature, pain, and chemical itch.

Friction Ridges

Elevated skin markings on the fingertips, palms, and soles formed by epidermal ridges overlying dermal ridges that improve grip and produce unique fingerprints via crest sweat pores.

Cleavage (Tension) Lines

Predominant parallel arrangements of collagen and elastic fibers in the reticular dermis; surgical incisions made parallel to them produce minimal gaping and faster healing.

Flexure Lines

Dermal folds and visible skin creases located near joints (palms, digits, wrists) where the dermis is firmly bound to underlying deep fascia to facilitate joint bending.

Striae

Silvery-white or purplish stretch marks resulting from tearing of collagen and elastic fibers in the reticular dermis following rapid mechanical stretching.

Blister

A fluid-filled pocket that forms when acute friction or burn causes separation between the epidermis and the underlying dermis, allowing tissue fluid to pool.

Eumelanin

A major form of the melanin pigment that produces a brownish-black color and is present in higher quantities in darker skin.

Pheomelanin

A sulfur-containing form of melanin pigment that produces a reddish-yellow color, prevalent in fair skin, red hair, and freckles.

Albinism

An autosomal recessive genetic condition characterized by a hereditary defect in the enzyme tyrosinase, resulting in little or no melanin production despite normal numbers of melanocytes.

Vitiligo

An acquired autoimmune disorder marked by the destruction and loss of melanocytes, resulting in well-demarcated depigmented white patches of skin.

Cyanosis

A bluish discoloration of the skin and mucous membranes resulting from oxygen deficiency and an excess of deoxygenated hemoglobin exceeding $5\,\text{g/dL}$ in capillary blood.

Erythema

Abnormal redness of the skin caused by increased cutaneous blood flow and dilation of dermal blood vessels during inflammation, fever, sunburn, or blushing.

Pallor

Abnormal paleness or ashen appearance of the skin caused by severe vasoconstriction, reduced cutaneous blood flow, shock, cold, or low hemoglobin concentrations.

Hematoma

A mass of clotted blood (bruise) trapped in the skin or subcutaneous tissues due to mechanical trauma or ruptured blood vessels.

Jaundice

Yellowish discoloration of the skin, mucous membranes, and sclera due to hyperbilirubinemia, indicating liver pathology, hemolysis, or biliary obstruction.

Petechiae

Minute, non-blanching red or purple punctate hemorrhages in the skin often caused by platelet deficiency (thrombocytopenia) or anticoagulant medications.

Freckles (Ephelides)

Flat, small, tan to light-brown melanized patches that become darker and more noticeable upon exposure to ultraviolet radiation.

Moles (Nevi)

Elevated, darker brown to black melanized skin lesions composed of aggregations of melanocytes that frequently grow hair and require clinical monitoring.

Capillary Hemangioma

A raised, bright red vascular birthmark ('strawberry hemangioma') caused by benign proliferations of dermal capillaries that usually regresses during early childhood.

Port-Wine Stain (Nevus Flammeus)

A flat, pinkish-to-purple vascular birthmark caused by abnormally dilated dermal capillaries that typically persists throughout life.

Lanugo

Fine, downy, unpigmented fetal hair that appears during the last three months of fetal development and is mostly shed before or shortly after birth.

Vellus

Fine, pale, short hair that replaces fetal lanugo and constitutes about two-thirds of the hair of women and one-tenth of that of men.

Terminal Hair

Coarse, longer, and heavily pigmented hair found on the scalp, eyebrows, and eyelashes, and in androgen-stimulated regions (pubic, axillary, and male facial hair) after puberty.

Anagen

The active growth phase of the hair cycle in which matrix cells divide rapidly, lasting approximately $6$ to $8\,\text{years}$ in the human scalp and accounting for $\sim 90\%$ of scalp hairs.

Catagen

The transitional regression phase of the hair cycle lasting $2$ to $3\,\text{weeks}$, during which mitosis ceases and the lower follicle degenerates.

Telogen

The resting phase of the hair cycle lasting $1$ to $2\,\text{months}$, during which the club hair remains dormant in the follicle before being shed.

Alopecia

Significant thinning of hair or baldness resulting from genetic factors, hormonal shifts, autoimmune conditions, chemotherapy, or severe scarring.

Hirsutism

Excessive growth of terminal, coarse hair in women in androgen-dependent regions, such as the face, chest, or abdomen, commonly linked to endocrine disorders.

Nail Matrix

The mitotically active proximal growth zone of the nail bed responsible for the formation and elongation of the keratinized nail plate.

Lunule

The opaque, whitish crescent located at the proximal end of the nail plate, obscured by the thickness of the underlying nail matrix.

Eponychium

A narrow fold of dead stratum corneum extending over the proximal border of the nail body, commonly called the cuticle.

Hyponychium

The thickened epidermal stratum corneum underlying the free edge of the nail that seals and secures the nail plate to the distal fingertip.

Koilonychia

An abnormal nail dystrophy characterized by thin, concave, spoon-shaped nail plates, commonly secondary to severe chronic iron-deficiency anemia.

Clubbing

Bulbous enlargement and increased longitudinal curvature of the fingertips and nail plates associated with chronic systemic hypoxemia from pulmonary or cardiac disease.

Beau's Lines

Transverse horizontal depressions across the nail plate resulting from temporary arrest of cell division in the nail matrix during severe acute illness or fever.

Eccrine (Merocrine) Sweat Glands

Abundant simple coiled tubular glands that release a watery perspiration directly onto the epidermal surface via sweat pores for thermoregulatory evaporative cooling.

Apocrine Sweat Glands

Large coiled tubular glands in the axillary and anogenital regions that secrete an odor-free, milky, protein- and lipid-rich fluid into hair follicles, activated primarily by puberty, emotional stress, and sexual excitement.

Bromhidrosis

Disagreeable, pungent body odor caused by bacterial decomposition of the fatty acids and organic compounds present in apocrine sweat.

Sebaceous Glands

Lobulated, flask-shaped cutaneous glands associated with hair follicles that release an oily mixture called sebum via holocrine secretion.

Sebum

An oily holocrine secretion rich in lipids and broken-down cellular debris that lubricates and waterproofs skin and hair and provides mild bactericidal activity.

Ceruminous Glands

Modified apocrine sweat glands located in the external acoustic meatus that produce cerumen (earwax) to coat guard hairs, repel water, and inhibit bacteria.

Myoepithelial Cells

Specialized contractile epithelial cells situated around the secretory bases of sweat glands that contract under sympathetic stimulation to propel perspiration through the ducts.

Diaphoresis

Copious sweating that produces noticeable wetness of the skin, during which an individual may lose up to approximately $1\,\text{L}$ of sweat per hour during intense exertion.

Insensible Perspiration

Unnoticed daily water loss across the skin of approximately $500\,\text{mL/day}$ that does not produce visible cutaneous wetness.

First-Degree Burn

A superficial burn limited to the epidermis, characterized by localized redness, mild edema, and pain, typically healing within several days without scarring.

Second-Degree Burn

A partial-thickness burn that destroys the epidermis and penetrates into the dermis, characterized by painful blister formation, red or mottled appearance, and a healing course of two weeks to several months.

Third-Degree Burn

A full-thickness burn destroying the entire epidermis, dermis, and often deeper tissues, appearing leathery, charred, or white, and lacking initial sensation due to destruction of cutaneous nerve endings.

Eschar

Burned, necrotic tissue resulting from severe full-thickness thermal burns that releases toxic substances and must be excised to permit wound healing.

Debridement

The essential clinical removal of dead tissue and eschar from a severe burn wound to mitigate systemic toxic effects and prevent infection.

Rule of Nines

A clinical system for calculating total body surface area ($\%\,\text{TBSA}$) burned in an adult by assigning anatomical regions percentages divisible by nine (such as $9\%$ for the entire head, $9\%$ for each entire upper limb, $18\%$ for anterior trunk, $18\%$ for posterior trunk, $18\%$ for each entire lower limb, and $1\%$ for the perineum).

Autograft

A skin graft harvested from an undamaged donor site on a patient's own body and transferred to the burned wound bed, carrying virtually no risk of immunological rejection.

Homograft (Allograft)

A temporary biological skin graft harvested from an unrelated cadaveric human donor to reduce fluid loss and prevent infection while awaiting autografting.

Heterograft (Xenograft)

A temporary biological wound covering derived from a donor of a different species, most commonly porcine (pig) skin.

Basal Cell Carcinoma

The most common and least malignant cutaneous neoplasm, arising from proliferating stem cells of the stratum basale that invade the dermis to form a shiny, pearl-like nodule.

Squamous Cell Carcinoma

A malignant neoplasm arising from keratinocytes of the stratum spinosum that typically manifests as a scaly, reddened papule or firm ulcer with potential to metastasize to regional lymph nodes.

Malignant Melanoma

The most aggressive and lethal form of skin cancer, originating from melanocytes, characterized by rapid metastasis and early invasion, and evaluated using the ABCDE criteria.