Chapter 5: The Integumentary System

Comprehensive vocabulary flashcards covering the structural components, strata, cell types, mechanoreceptors, accessory structures, and exocrine glands of the integumentary system.

Cutaneous Membrane

The skin, consisting of a superficial epidermis and a deeper dermis, which forms the outer protective barrier of the body.

Epidermis

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

Dermis

The highly vascular layer of the skin deep to the epidermis that provides blood supply, anchors the epidermis, and houses sensory receptors.

Papillary Layer

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

Dermal Papillae

Projections of the papillary layer that house capillaries providing oxygen and nutrients to the avascular epidermis.

Reticular Layer

The deeper layer of the dermis composed of dense irregular collagenous connective tissue containing collagen and elastic fibers, proteoglycans, hair follicles, and glands.

Hypodermis

Subcutaneous tissue or superficial fascia deep to the dermis, not technically part of the skin, composed of loose connective tissue, adipose tissue, and blood vessels that anchor skin to muscle and bone.

Merkel Cell Fiber

A sensory mechanoreceptor in the skin responsible for discriminative touch with fine spatial resolution.

Tactile Corpuscle

A mechanoreceptor located in the dermal papillae that detects discriminative light touch with less spatial resolution to help distinguish shape and texture.

Ruffini Ending

A bulbous mechanoreceptor in the dermis that detects stretch and movement.

Lamellated Corpuscle

A sensory Pacinian receptor located deep in the reticular dermis that responds to vibration and deep pressure.

Keratinocytes

The predominant epithelial cells of the epidermis that manufacture the fibrous protein keratin and are linked together by desmosomes to resist mechanical stress.

Stratum Basale

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

Stratum Spinosum

Usually the thickest epidermal layer, consisting of metabolically active cells that accumulate keratin and appear spiny due to filaments attached to desmosomes.

Stratum Granulosum

The middle epidermal layer consisting of $3\text{--}5$ rows of cells containing keratin bundles and lipid-containing granules that form a waterproof barrier.

Stratum Lucidum

A thin, translucent layer of dead keratinocytes found exclusively in thick skin to provide an extra layer of protection.

Stratum Corneum

The most superficial epidermal layer composed of multiple layers of dead, flattened keratinocytes filled with keratin and lacking organelles, which are shed through exfoliation.

Keratinocyte Life Cycle Duration

The complete progression of a keratinocyte dividing in the stratum basale, moving superficially, dying, and shedding from the stratum corneum, which takes $40\text{--}50\text{ days}$.

Melanocytes

Epidermal cells located primarily in the stratum basale that synthesize the pigment melanin.

Dendritic Cells

Phagocytic Langerhans cells in the epidermis that detect pathogens and help coordinate immune responses.

Thick Skin

Skin that contains all five epidermal strata (including stratum lucidum), possesses abundant sweat glands, and lacks hair follicles and sebaceous glands; located on palms, soles, and fingertips.

Thin Skin

Skin that lacks the stratum lucidum, covers most of the body, allows flexibility, and contains numerous hair follicles and sebaceous glands.

Melanosomes

Specialized intracellular vesicles within melanocytes where tyrosine is converted into melanin via the enzyme tyrosinase.

Tyrosinase

The enzyme within melanocytes that catalyzes the chemical reactions that join two molecules of the amino acid tyrosine to produce melanin.

Albinism

A condition in which melanocytes fail to manufacture the enzyme tyrosinase, resulting in an absence of skin, hair, and eye pigmentation.

Hair Shaft

The portion of the hair that projects above the skin surface, composed of dead cells that have completed keratinization.

Hair Root

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

Hair Matrix

The group of actively dividing epithelial cells located in the hair bulb that produces the hair.

Hair Papilla

A connective tissue projection at the base of the hair bulb containing blood vessels that nourish the dividing cells of the hair matrix.

Arrector Pili Muscle

A small band of smooth muscle attached to the hair follicle whose contraction pulls the hair upright to generate goosebumps.

Hair Cuticle

The outermost single layer of overlapping keratinocytes containing hard keratin that compacts underlying layers and provides abrasion resistance.

Hair Cortex

The middle layer of the hair shaft composed of several layers of hard keratin-filled cells that contain most of the pigment responsible for hair color.

Hair Medulla

The inner core of keratinocytes containing soft keratin, present only in thick hairs such as those on the head.

Nail Plate

The hard exterior structure of the nail resting on the epidermal nail bed, divided into the visible nail body and the concealed nail root.

Nail Matrix

The thickened proximal portion of the nail root containing actively dividing cells that push older cells distally to grow the nail.

Eponychium

The cuticle of the nail, representing the most distal part of the proximal nail fold and composed solely of stratum corneum.

Hyponychium

The accumulation of stratum corneum underlying the free edge of the nail plate where it attaches to the distal nail bed.

Lunula

The opaque, whitish crescent region at the base of the nail body lying over the thickened nail matrix where cells accumulate keratin.

Eccrine Sweat Glands

Simple coiled tubular glands situated in the dermis that release a $99\%$ water secretion via sweat pores primarily for thermoregulation.

Apocrine Sweat Glands

Glands located in the axillae, anal area, and areola that release a protein-rich secretion into hair follicles beginning at puberty, producing odor upon bacterial breakdown.

Ceruminous Glands

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

Mammary Glands

Specialized sweat glands that produce milk, a nutrient-rich secretion composed of lipids, proteins, and sugars to nourish infants.

Sebaceous Glands

Branched exocrine glands composed of secretory acini that empty sebum into hair follicles via holocrine secretion under the influence of sex hormones like testosterone.

Sebum

An oily lipid mixture produced by sebaceous glands that coats the skin and hair to prevent dehydration and deter bacterial growth.