LESSON #5: INTEGUMENTARY SYSTEM | SEELEY’S 13TH EDITION

Vocabulary flashcards covering key terms and concepts from the integumentary system lecture notes (Seeley’s 13th ed.).

Avascular

Epidermis lacks blood vessels and is nourished by diffusion from capillaries in the dermal papillary layer.

Epidermis

The outer protective layer of skin composed of stratified squamous epithelium; separated from the dermis by the basement membrane.

Basement membrane

Thin layer that separates the epidermis from the dermis and anchors them together.

Keratinocytes

The most abundant epidermal cells that produce keratin for strength and form the epidermal layers.

Melanocytes

Cells that produce melanin; contribute to skin color and transfer melanin to keratinocytes; same number in all people.

Melanin

Pigment produced by melanocytes derived from tyrosine; provides UV protection and contributes to skin color.

Langerhans cells

Epidermal immune cells involved in the body’s defense system.

Merkel cells

Epidermal cells that detect light touch and superficial pressure.

Keratinization

Process by which cells move outward, fill with keratin, die, and form a resistant, protective permeability layer.

Stratum basale (germinativum)

Deepest epidermal layer; single layer of cuboidal/columnar cells with high mitotic activity; desmosomes; ~40–56 days to reach surface.

Desmosomes

Cell–cell junctions that hold keratinocytes together and provide structural strength.

Stratum spinosum

8–10 layers of cells that flatten as they move upward; contains desmosomes and keratin fibers.

Stratum granulosum

2–5 layers of flattened cells with keratohyalin granules; lamellar bodies release lipids; nucleus degenerates as cells die.

Stratum lucidum

Thin, clear layer found only in thick skin (palms and soles).

Stratum corneum

Most superficial layer; 25+ layers of dead, keratinized cells joined by desmosomes; forms the protective barrier.

Thick skin

Skin with all five epidermal strata; found on palms, fingertips, and soles; contains friction ridges.

Thin skin

Skin lacking stratum lucidum; covers most of the body; more flexible and contains hair.

Dermis

Deeper connective tissue layer; provides structural strength and houses nerves, blood vessels, glands, and hair follicles.

Papillary dermis

Superficial dermal layer (areolar CT) with dermal papillae and capillary beds; contains touch receptors.

Reticular dermis

Deep dermal layer (dense irregular CT) with collagen and elastic fibers; houses glands and hair follicles.

Papillae

Projections of the dermis that elevate the epidermis, forming fingerprints and enhancing grip.

Meissner corpuscles

Touch receptors located in the papillary dermis.

Pacinian corpuscles

Deep pressure receptors in the dermis, sensitive to vibration.

Ruffini endings

Touch/pressure receptors in the dermis that respond to skin stretch.

Cleavage (tension) lines

Directions of collagen fiber orientation in the dermis; important for surgical incisions and scar formation.

Subcutaneous tissue (hypodermis)

Loose connective tissue (and adipose) beneath the skin; not part of the skin; anchors skin to underlying structures.

Hair

Strands of keratinized cells growing from hair follicles; color due to melanin.

Lanugo

Fine, unpigmented fetal hair.

Terminal hair

Long, coarse hair of the scalp, eyebrows, and, at puberty, axillae, pubic region, and face.

Vellus hair

Fine, short, lightly pigmented hair covering most of the body.

Arrector pili

Smooth muscle attached to hair follicles; contraction causes hair to stand (goose bumps).

Sebaceous glands

Holocrine glands that secrete sebum to lubricate skin and hair; usually open into hair follicles.

Eccrine glands

Merocrine glands; abundant on palms and soles; secrete isotonic sweat for thermoregulation directly onto skin.

Apocrine glands

Glands active at puberty; open into hair follicles; secretions can become odorous after bacterial action.

Ceruminous glands

Modified apocrine glands in the external ear canal; produce earwax (cerumen).

Mammary glands

Modified apocrine sweat glands that produce milk.

Nail body

Visible part of the nail made of layered dead keratinocytes.

Eponychium (cuticle)

Fold of skin at the proximal nail edge; the cuticle overlaying the nail root.

Hyponychium

Skin underneath the free edge of the nail.

Nail matrix

Cells at the nail root that produce the nail plate.

Nail bed

Skin beneath the nail plate; contains the nail matrix.

Lunula

Whitish crescent area at the base of the nail indicating the visible part of the nail matrix.

Nail growth rate

Fingernails grow about 0.5–1.2 mm per day; toenails grow more slowly.

Hair shaft

Part of the hair that extends above the surface of the skin.

Medulla

Central core of the hair.

Cortex

Forms the bulk of the hair shaft.

Cuticle (hair)

Outer protective layer of hair consisting of overlapping cells.