BIOL 40A: Unit 1 - The Integumentary System

Comprehensive vocabulary flashcards covering the anatomy, histology, accessory organs, homeostatic functions, clinical disorders, burns, wound healing, and embryology of the integumentary system.

Integumentary System

The body system composed of the skin, hair, and nails that provides protection, thermoregulation, waste excretion, sensory perception, and vitamin D synthesis.

Epidermis

The most superficial, thinner portion of the skin, composed of stratified keratinized epithelial tissue.

Dermis

The deeper layer of the skin located beneath the epidermis, composed primarily of dense irregular and areolar connective tissue.

Hypodermis

Also called the subcutaneous (subQ) layer; a layer located deep to the dermis consisting of areolar and adipose tissue that anchors the skin while not being part of the skin itself.

Deep Fascia

A dense connective tissue layer located deep to the hypodermis that invests and encloses underlying muscles.

Keratinocytes

The most abundant epidermal cells; arranged in multiple layers, they synthesize the fibrous protein keratin, which protects against abrasion and water loss.

Melanocytes

Epidermal cells with long projections that contain melanosomes and synthesize melanin to protect cell nuclei from ultraviolet (UV) radiation damage.

Dendritic Cells (Langerhans Cells)

Immune surveillance cells located in the stratum spinosum that recognize, process, and present foreign antigens during immune responses.

Tactile Epithelial Cells (Merkel Cells)

Sensory cells located in the stratum basale that make contact with nonencapsulated sensory corpuscles to detect light touch sensations.

Melanosome

A specialized intracellular organelle found within melanocytes in which the pigment melanin is synthesized and stored.

Freckles

Patches of accumulated melanin occurring in genetically predisposed individuals that appear reddish or brown and become more pronounced with summer sun exposure.

Age Spots

Darker, permanent accumulations of melanin that develop over time from sunlight exposure, do not fade during winter months, and are common in adults over $40$.

Nevus

Commonly known as a mole; a round, flat, or raised benign localized overgrowth of melanocytes that typically develops in childhood or adolescence.

Albinism

An inherited genetic condition marked by an inability to produce melanin, resulting in total or partial absence of pigment in the skin, hair, and eyes.

Stratum Basale

The deepest epidermal layer, consisting of a single row of cuboidal or columnar actively mitotic stem cells that produce new keratinocytes, as well as melanocytes and tactile epithelial cells.

Stratum Spinosum

An epidermal layer composed of $8$ to $10$ rows of spiny-appearing keratinocytes bound by desmosomes that provide strength and flexibility; contains dendritic cells.

Stratum Granulosum

An epidermal layer made of $3$ to $5$ rows of flattened keratinocytes undergoing apoptosis and organelle degeneration, accumulating lamellar granules filled with lipid secretions.

Stratum Lucidum

A clear epidermal layer found exclusively in thick skin (palms, digits, soles) consisting of $4$ to $6$ rows of flat, dead keratinocytes packed with dense keratin.

Stratum Corneum

The outermost epidermal stratum composed of $20$ to $50$ rows of dead, flattened keratinocytes packed with keratin that provide a waterproof barrier against abrasion and microbes.

Lamellar Granules

Membrane-bound vesicles within keratinocytes of the stratum granulosum that exocytose a lipid-rich secretion to water-repel and seal the epidermis.

Provitamin D

A 7-dehydrocholesterol precursor molecule present in the epidermis that undergoes conversion when exposed to ultraviolet (UV) sunlight.

Calcitriol

The fully active hormonal form of vitamin D ($1,25\text{-dihydroxyvitamin D}_3$), synthesized via enzymatic processing in the liver and kidneys, which promotes intestinal calcium absorption.

Thin Skin

Skin covering most of the body except palms and soles; lacks a stratum lucidum, contains hair follicles and sebaceous glands, and has fewer sweat glands and sensory receptors.

Thick Skin

Skin present on the palms, palmar digits, soles, and plantar toes; possesses a stratum lucidum, epidermal ridges, and abundant sensory receptors, but lacks hair follicles and sebaceous glands.

Papillary Dermis

The superficial one-fifth of the dermis composed of areolar connective tissue containing dermal papillae, capillary loops, free nerve endings, and tactile corpuscles.

Reticular Dermis

The deeper, thicker region of the dermis composed of dense irregular connective tissue with bundles of collagen and coarse elastic fibers, giving skin strength and elasticity.

Dermal Papillae

Small, nipple-shaped projections of the papillary dermis extending into the undersurface of the epidermis that increase surface area for vascular exchange and house sensory corpuscles.

Epidermal Ridges

Surface contours and downward projections of the epidermis on hands and feet (fingerprints) that enhance grip, friction, and tactile sensitivity.

Epidermal Pegs

Downward epithelial extensions of the epidermis that interlock with dermal papillae to form a strong mechanical junction resisting separation.

Shear Forces

Opposing mechanical forces that attempt to slide the epidermis across the underlying dermis, counteracted by the interlocking peg-and-papilla architecture.

Stretch Marks

Silvery white streaks (striae) resulting from extreme dermal stretching that tears collagen and elastic fibers, followed by replacement with poorly vascularized scar tissue.

Dermal Vasodilation

The widening of blood vessels in the dermis that increases cutaneous blood flow and heat radiation to lower body temperature during heat exposure or exercise.

Dermal Vasoconstriction

The narrowing of cutaneous blood vessels in response to cold, which shunts blood to internal organs to conserve body heat.

Tattoo Inking Layer

The dermis; target layer of tattoo needles where ink remains permanent because dermal collagen is not constantly shed like epidermal cells.

Tattoo Removal Mechanism

A medical laser technique that shatters ink pigments into microscopic fragments small enough to be phagocytized and cleared by lymphatic and immune cells.

Tactile Corpuscles (Meissner Corpuscles)

Encapsulated sensory nerve receptors located inside dermal papillae that detect light touch, fine pressure, and slow vibrations.

Lamellar Corpuscles (Pacinian Corpuscles)

Large, layered oval sensory receptors located deep in the reticular dermis or hypodermis that respond to deep pressure and rapid vibrations.

Free Nerve Endings

Unencapsulated sensory dendrites terminating in the papillary dermis and deeper epidermis that detect pain, temperature, tickle, and itching.

Sebaceous Glands

Exocrine oil glands connected to hair follicles that synthesize and secrete sebum; largely inactive in childhood and activated by hormones at puberty.

Sebum

An oily mixture of triglycerides, cholesterol, proteins, and inorganic salts that coats hair shafts, lubricates the skin, and inhibits certain bacteria.

Holocrine Gland

A secretory gland type, exemplified by sebaceous glands, where the entire cell ruptures, dies, and forms part of the secretion product.

Acne

An inflammatory skin condition involving plugged hair follicles, excess sebum production, and bacterial proliferation causing pimples and pustules.

Cutibacterium acnes (C. acnes)

The anaerobic bacterial species that colonizes sebum-rich follicles, metabolizes lipids, and provokes inflammatory immune responses in acne.

Pus

A thick, yellowish-white fluid that accumulates at sites of follicular infection consisting of sebum, dead skin cells, bacteria, and dead white blood cells.

Sudoriferous Glands

Sweat-producing exocrine glands that release secretions onto the skin surface or into hair follicles via excretory ducts.

Eccrine Sweat Glands

The most abundant sweat glands, functional from birth and distributed across most skin; secrete watery, acidic sweat for thermoregulation, excretion, and microbial protection.

Apocrine Sweat Glands

Sweat glands functional from puberty, located in the axillae, groin, areolae, and male bearded face; secrete a viscous, milky sweat that produces body odor upon bacterial breakdown.

Merocrine Secretion

The secretory mechanism where glandular products are discharged via exocytosis without injury or cytoplasm loss to the cell; utilized by both eccrine and apocrine sweat glands.

Ceruminous Glands

Modified apocrine sweat glands situated in the external auditory canal that secrete cerumen.

Cerumen

Earwax; a sticky waxy secretion from ceruminous and sebaceous glands that provides a physical and chemical barrier against water, foreign particles, and insects.

Mammary Glands

Specialized modified apocrine sweat glands within the breasts that are hormonally regulated to produce and secrete milk.

Hair Shaft

The superficial, visible portion of a hair that projects beyond the epidermal surface.

Hair Root

The portion of a hair embedded deep below the epidermal surface, penetrating into the dermis and sometimes the hypodermis.

Hair Follicle

The tubular epidermal invagination that encloses the hair root, consisting of an internal and external epithelial root sheath surrounded by a dermal root sheath.

Hair Bulb

The expanded onion-shaped base of the hair follicle housing the hair matrix and surrounding the vascular papilla of the hair.

Hair Matrix

A germinal layer of actively dividing epithelial stem cells in the hair bulb that gives rise to all cellular layers of the growing hair.

Papilla of the Hair

A vascularized connective tissue projection that indents the hair bulb, providing blood vessels and nutrients to the actively dividing hair matrix cells.

Arrector Pili Muscle

A smooth muscle bundle extending from the papillary dermis to the connective tissue sheath of the hair follicle that contracts under cold or emotional stress to pull hair upright.

Hair Root Plexus

A network of unmyelinated sensory nerve endings wrapped around the base of the hair follicle that detects hair shaft displacement.

Growth Stage (Hair Cycle)

The active follicular cycle phase where stem cells in the hair matrix divide rapidly, pushing older cells upward as they keratinize and lengthen the hair.

Regression Stage (Hair Cycle)

The transition phase of hair growth where matrix division halts, the follicle atrophies, and the hair root detaches from its vascular papilla.

Resting Stage (Hair Cycle)

The quiescent phase of the hair cycle following regression in which the old hair club falls out before new matrix division initiates a new cycle.

Androgenic Alopecia

Male-pattern baldness; a genetically predetermined progressive hair miniaturization and shedding pattern influenced by androgens.

Vellus Hairs

Fine, short, lightly pigmented hairs covering the bodies of children and constituting the majority of body hair in adult females.

Terminal Hairs

Long, coarse, heavily pigmented hairs found on the scalp, eyebrows, and eyelashes, and developing at puberty in the axillae, pubic regions, and male face.

Lanugo

Extremely fine, unpigmented fetal hairs that develop around the fifth to sixth month of gestation and are normally shed prior to birth; can re-emerge in severe anorexia.

Eumelanin

The dark brown-to-black variant of melanin pigment responsible for darker shades of hair and skin.

Pheomelanin

The yellow-to-red variant of melanin pigment responsible for red and blond hair colors.

Gray Hair

Hair characterized by a progressive, age-related decline in melanin synthesis by matrix melanocytes.

White Hair

Hair that completely lacks melanin pigment and contains microscopic air bubbles within the medullary shaft.

Pinpoint Bleeding (Waxing)

Tiny droplets of blood appearing after hair extraction caused by mechanical disturbance of delicate capillary loops nourishing the hair follicle base.

Laser Hair Removal

A procedure utilizing specific wavelengths of light absorbed by hair pigment to generate heat and selectively destroy the regenerative hair follicle.

Nail Body (Nail Plate)

The visible external portion of the nail resting firmly on the underlying nail bed.

Free Edge

The distal, unattached portion of the nail plate extending outward beyond the fingertip or toe.

Nail Bed

The specialized layer of living epidermal tissue situated beneath the nail plate that extends from the matrix to the hyponychium.

Nail Root

The proximal, hidden portion of the nail plate buried beneath a fold of skin known as the proximal nail fold.

Nail Matrix

The thickened, actively dividing germinal epithelium located proximal to the nail root that produces new, highly keratinized nail cells.

Lunule (Lunula)

The opaque, white, crescent-shaped region at the proximal base of the nail body overlying the thick vascular nail matrix.

Eponychium

Also called the cuticle; a narrow fold of stratum corneum from the proximal nail fold extending onto the proximal border of the nail body.

Hyponychium

The thickened zone of stratum corneum located beneath the free edge that seals the nail plate securely to the fingertip.

Regeneration

The biological repair process for superficial tissue injuries where lost cells are replaced by identical cell division, restoring complete normal anatomy and function.

Fibrosis

The repair process for extensive deep injuries where fibroblasts synthesize dense collagen connective tissue, producing a non-functional scar.

Epidermal Wound Healing

The repair of superficial wounds (such as abrasions) wherein detached basal cells enlarge, migrate across the wound bed, and cease migrating upon contact inhibition before dividing to restore strata thickness.

Hemostasis

The immediate first phase of deep wound repair involving vascular spasm and platelet-fibrin clot formation to arrest hemorrhage within minutes.

Inflammatory Phase

The second phase of deep wound healing (days $1$ to $4$) where increased vascular permeability allows neutrophils and macrophages to phagocytize microbes and cellular debris.

Proliferative Phase

The third phase of deep wound healing (days $3$ to $21$) marked by fibroblast proliferation, extensive collagen deposition, angiogenesis, and granulation tissue growth.

Granulation Tissue

Vascular, pink, granular connective tissue formed by proliferating capillaries and fibroblasts that fills the void of an open wound during the proliferative phase.

Maturation (Remodeling) Phase

The final stage of deep wound healing occurring from day $21$ onwards where the scab sloughs, collagen fibers are reorganized and cross-linked, and scar tissue gains tensile strength.

Primary Intention Healing

Healing of a clean, sharp incision with minimal tissue deficit where opposing wound edges are closely approximated with sutures, staples, or glue, resulting in minimal scarring.

Secondary Intention Healing

Healing of wide, irregular, or infected wounds with significant tissue loss that cannot be surgically approximated, healing from the base upward via granulation tissue and leaving noticeable scars.

Tertiary Intention Healing

Also called delayed primary closure; intentional temporary management where an infected or heavily contaminated wound is left open to drain and debride before being surgically sutured closed.

First-Degree Burn

A mild thermal injury confined strictly to the epidermis, characterized by localized erythema, mild edema, and pain without blister formation (e.g., typical sunburn).

Second-Degree Burn

A partial-thickness burn that damages the epidermis and upper portions of the dermis, characterized by redness, edema, pain, and blister formation.

Third-Degree Burn

A full-thickness burn that completely destroys the epidermis, dermis, and subcutaneous layer; appears white, red, or charred black, and lacks sensation due to destroyed nerve endings.

Major Burn

A severe burn injury defined as any third-degree burn involving the face, hands, feet, or perineum; third-degree burns exceeding $10\%$ body surface area; or second-degree burns exceeding $25\%$ body surface area.

Rule of Nines

A clinical estimation method dividing adult body surface area into sections of $9\%$ or multiples of $9\%$ ($9\%$ head, $18\%$ each leg, $36\%$ trunk, $9\%$ each arm, $1\%$ perineum) to calculate the extent of burn injuries.

Skin Graft

The surgical transfer of a section of healthy donor skin to cover a full-thickness wound where stratum basale stem cells have been permanently destroyed.

Basal Cell Carcinoma (BCC)

The most common skin cancer ($78\%$ of cases), arising from stem cells in the stratum basale; slow-growing and rarely metastasizing, it classically appears as a pearly, shiny bump with rolled borders.

Squamous Cell Carcinoma (SCC)

The second most common skin cancer ($20\%$ of cases), originating from keratinocytes of the stratum spinosum; presents as a scaly, rough, erythematous patch or firm nodule with variable metastatic potential.

Malignant Melanoma

The most dangerous and lethal form of skin cancer ($2\%$ of cases), arising from transformed melanocytes; metastasizes aggressively through lymphatic and vascular pathways.