Chapter 5: The Integumentary System

Comprehensive vocabulary flashcards covering the anatomy, histology, physiological functions, and accessory structures of the integumentary system.

Integumentary System

The organ system consisting of the skin (cutaneous membrane) and accessory structures including hair, nails, and glands.

Epidermis

The most superficial layer of the skin, composed of keratinized stratified squamous epithelium resting on a basement membrane.

Dermis

The highly vascular layer of skin deep to the epidermis that provides blood supply, houses sensory receptors, and anchors the epidermis; divided into the papillary and reticular layers.

Papillary Layer

The thin, superficial layer of the dermis composed of loose (areolar) connective tissue that contains dermal papillae and tactile corpuscles.

Dermal Papillae

Projections of the dermis that house capillaries to provide oxygen and nutrients to the avascular epidermis.

Reticular Layer

The deep dermal layer composed of dense irregular collagenous connective tissue, rich in proteoglycans, collagen, elastic fibers, sensory receptors, blood vessels, and hair follicles.

Hypodermis

A layer deep to the dermis (also called superficial fascia or subcutaneous tissue) composed of loose connective tissue, blood vessels, and adipose tissue; anchors skin to underlying muscle and bone but is not part of the skin.

Arrector Pili Muscles

Bands of smooth muscle attached to hair follicles whose contraction pulls the hair upright, creating goosebumps.

Merkel Cell Fiber

A cutaneous mechanoreceptor located in the skin that functions in discriminative touch with fine spatial resolution.

Tactile (Meissner) Corpuscle

A sensory receptor housed within the dermal papillae that detects light touch and discriminative touch with less spatial resolution.

Ruffini Ending (Bulbous Corpuscle)

A sensory mechanoreceptor in the dermis that responds to stretch and movement.

Lamellated (Pacinian) Corpuscle

A large sensory receptor located deep in the reticular layer of the dermis that detects vibration and deep pressure applied to the skin.

Cutaneous Mechanoreceptors

Sensory receptors embedded in the skin that detect external mechanical stimuli such as fine touch, crude touch, stretch, movement, vibration, and deep pressure.

Keratinocyte

The predominant cell type in the epidermis; epithelial cells that produce the fibrous protein keratin and are linked together by desmosomes to resist mechanical stress.

Epidermal Strata

The distinct layers of keratinocytes in the epidermis, arranged from deep to superficial as stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.

Stratum Basale

The deepest epidermal layer consisting of a single row of dividing stem cells attached to the basement membrane, from which all epidermal keratinocytes originate.

Stratum Spinosum

Usually the thickest epidermal layer; contains metabolically and mitotically active cells that accumulate keratin filaments attached to desmosomes, giving them a spiny appearance.

Stratum Granulosum

The middle epidermal layer consisting of $3\text{--}5$ rows of cells containing granules of keratin bundles and membrane-coating lipids that form a waterproof barrier, which cuts off nutrients and causes cells to die.

Stratum Lucidum

A thin, translucent layer of dead keratinocytes found only in thick skin that provides an extra layer of protection.

Stratum Corneum

The most superficial epidermal layer, consisting of multiple layers of dead, flattened keratinocytes filled with keratin that lack organelles and are continuously shed by exfoliation.

Keratinocyte Life Cycle

The $40\text{--}50\text{ day}$ progression in which a keratinocyte arises through mitosis in the stratum basale, moves upward while accumulating keratin, dies in the stratum granulosum, and is eventually sloughed from the stratum corneum.

Melanocyte

A cell located primarily in the stratum basale of the epidermis that synthesizes the pigment melanin.

Merkel Cell

A sensory cell located in the epidermis that is involved in the sensation of touch.

Dendritic (Langerhans) Cell

A phagocytic immune cell in the epidermis that detects pathogens and coordinates immune responses.

Thick Skin

Skin found on the palms of the hands, soles of the feet, and fingertips; possesses all five strata including stratum lucidum, lacks hair follicles and sebaceous glands, and contains numerous sweat glands.

Thin Skin

Skin covering most of the body; lacks the stratum lucidum, provides flexibility, and contains hair follicles and sebaceous glands.

Melanin

A skin pigment composed of two molecules of tyrosine joined by tyrosinase; absorbs and dissipates UV radiation to protect epidermal DNA and reduces vitamin D synthesis.

Melanosome

A specialized vesicle within a melanocyte where melanin synthesis reactions occur and from which pigment is transferred into neighboring keratinocytes.

Tyrosinase

The enzyme responsible for catalyzing the series of reactions that convert two tyrosine molecules into melanin.

Albinism

A condition characterized by an absence of skin, hair, and eye pigmentation resulting from melanocytes failing to manufacture the enzyme tyrosinase.

Hair Shaft

The portion of hair that projects above the skin surface, composed entirely of dead, completely keratinized epithelial cells.

Hair Root

The portion of hair located below the skin surface within the hair follicle, containing living cells actively undergoing keratinization.

Hair Bulb

The expanded base of the hair root containing the hair matrix and the hair papilla.

Hair Matrix

A group of actively dividing epithelial cells located within the hair bulb that actively produces the hair as new cells are pushed upward.

Hair (Dermal) Papilla

A connective tissue projection housing blood vessels at the base of the hair bulb that provides nutrients to the dividing cells of the hair matrix.

Hair Follicle

An invagination of the epithelium that wraps around the hair root; composed of an epithelial root sheath and a surrounding connective tissue dermal root sheath.

Transverse Section of a Hair Shaft

A cross section revealing the three concentric regions of hair: an inner central medulla, a middle cortex containing pigment and hard keratin, and an outer single-layered cuticle.

Medulla (Hair)

The central core of a hair shaft, present only in thick hairs (such as those on the head), composed of keratinocytes with soft keratin.

Cortex (Hair)

The intermediate layer of a hair shaft consisting of several layers of keratinocytes containing hard keratin and pigment responsible for hair color.

Cuticle (Hair)

The outermost layer of a hair shaft consisting of a single layer of overlapping keratinocytes filled with hard keratin to compact underlying layers and resist abrasion.

Sagittal Section of a Fingertip

A cross-sectional view of digit anatomy illustrating the nail root, nail bed, nail matrix, eponychium, lunula, nail body, and hyponychium.

Nail Plate

The rigid structural component of a nail sitting atop the epidermal nail bed, divided into the visible nail body and the embedded nail root.

Nail Matrix

The portion of the nail root containing actively dividing cells that produce the nail plate by pushing older keratinized cells distally.

Eponychium

The most distal part of the proximal nail fold (cuticle) consisting solely of stratum corneum that covers the nail root.

Hyponychium

An accumulation of stratum corneum found at the distal end of the nail attached to the underlying nail bed beneath the free edge.

Lunula

An opaque, white, crescent-shaped region near the proximal nail fold that overlies the thickened distal part of the nail matrix.

Eccrine Sweat Glands

Simple coiled tubular glands in the dermis that release a watery sweat ($99\%$ water) through an epidermal pore primarily for thermoregulation.

Apocrine Sweat Glands

Large sweat glands found in the axillae, anal area, and areolae that empty a protein-rich secretion into hair follicles, producing body odor upon bacterial metabolism; activated at puberty.

Ceruminous Glands

Modified apocrine sweat glands in the external ear canal that secrete cerumen (ear wax) to lubricate the tympanic membrane and trap debris.

Mammary Glands

Specialized sweat glands in the breast that produce milk containing proteins, lipids, and sugars to nourish a newborn infant.

Sebaceous Glands

Branched exocrine glands composed of acini that empty into hair follicles to secrete an oily mixture called sebum via holocrine secretion.

Sebum

A lipid-rich secretion produced by sebaceous glands that coats and moistens the skin and hair, prevents dehydration, and deters bacterial growth.