Integumentary System: Epidermis, Dermis, Hypodermis, Glands, Hair, and Nails

Comprehensive vocabulary flashcards covering the structure and function of the integumentary system: the epidermis, dermis, hypodermis, cutaneous glands, hair, and nails.

Epidermis

The top layer of skin, composed of stratified squamous epithelial tissue.

Stratum Corneum

The outermost epidermal layer consisting of $20$ to $30$ dead cell layers; its thick, keratinized cells protect deeper layers and regularly shed from the body.

Stratum Lucidum

The 'clear layer' of the epidermis consisting of a thin layer of translucent cells, found exclusively in thick skin on the palms of hands and soles of feet.

Stratum Granulosum

The epidermal layer where cells begin to flatten and disintegrate, accumulating keratin granules that water-protect the skin.

Stratum Spinosum

The 'spiny layer' named for the irregular shape of its cells; it is several cells thick and contains pre-keratin filaments.

Stratum Basale

The deepest epidermal layer, characterized by constantly dividing cells that push upward into the next layer.

Layers of the Epidermis (Diagram)

The stratified structure of the epidermis arranged from deep to superficial: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (thick skin only), and stratum corneum.

Melanocytes

Spider-shaped epithelial cells located in the bottom $2$ layers of the epidermis that produce the pigment melanin.

Melanin

A pigment produced by melanocytes and absorbed by nearby epidermal cells to protect the skin against harmful UV rays.

Melanoma

A form of skin cancer caused by the uncontrolled division of melanocytes.

Basal Cell Carcinoma

A form of skin cancer resulting from the uncontrolled division of cells in the stratum basale layer.

Squamous Cell Carcinoma

A form of skin cancer resulting from the uncontrolled division of cells in the stratum spinosum layer.

Dermis

The skin layer located just deep to the epidermis; composed of dense irregular connective tissue and containing blood vessels, nerves, sweat glands, and hair follicles.

Dermal Papillae

The wavy boundary between the epidermis and dermis that creates epidermal ridges (fingerprints), increasing friction to help pick up objects more easily.

Papillary Layer

The superficial layer of the dermis composed of loose connective tissue.

Reticular Layer

The deeper layer of the dermis composed of bundles of collagen fibers.

Integumentary Layers (Histology)

A microscopic cross-section displaying the cellular layers of the skin, including the superficial epidermis and the underlying dermis with its papillary and reticular layers.

Lines of Cleavage (Lines of Tension)

Patterns formed by the arrangement of collagen fibers in the dermis; surgical cuts are made parallel to these lines to aid healing.

Decubitus Ulcers

Also known as bedsores; localized injuries to skin and underlying tissue that form when blood supply is restricted for a prolonged time.

Hypodermis (Subcutaneous Layer)

A layer beneath the dermis that is not actually part of the skin, composed of loose fatty connective tissue that anchors skin to muscle or bone, provides insulation, and stores nutrients.

Eccrine Sweat Glands

Abundant merocrine sudoriferous glands found on the palms, soles of the feet, and forehead; structured as long tubes that open directly into pores on the skin surface.

Apocrine Sweat Glands

Sudoriferous glands found almost exclusively in the armpit and genital areas that secrete sweat containing fats and proteins.

Sweat

A generally acidic secretion consisting of $99\%$ water with trace amounts of salts, vitamins, wastes, and the antimicrobial peptide dermcidin.

Dermcidin

An antimicrobial peptide found in sweat that helps protect the body by killing bacteria on the skin surface.

Sebaceous Glands

Holocrine glands (whole burst cells) that secrete sebum onto hair; abundant on the scalp and face, and completely absent from the palms and soles of the feet.

Sebum

An oily substance secreted by sebaceous glands that lubricates the skin and hair and kills bacteria.

Cutaneous Appendages and Glands (Diagram)

Anatomical block section showing the structural relationships among hair follicles, sudoriferous (sweat) glands, and branching sebaceous (oil) glands within the skin.

Hard Keratin

The tough, fibrous structural protein that forms both hair and nails.

Hair Shaft

The part of the hair that projects above the surface of the skin, protected by an outermost layer called the cuticle.

Hair Follicle

The dermal sheath surrounding the root of the hair, containing the hair bulb where cell division occurs.

Hair Bulb

The expanded base of the hair follicle where epithelial cells divide, fill with keratin and pigment, and are pushed outward to form the hair strand.

Arrector Pili

Tiny smooth muscles attached to the hair follicle that contract to pull the hair upright, causing hair to 'stand on end'.

Nail Matrix

The thickened proximal portion of the nail bed responsible for producing heavily keratinized cells that form the nail body.

Lunula

The white, crescent-shaped 'little moon' area visible over the thickened nail matrix at the base of the nail body.

Eponychium (Cuticle)

The fold of skin at the proximal border of the nail body that provides a protective seal for the underlying nail matrix.

Nail Anatomy (Diagram)

The structural anatomy of the nail unit, featuring visible elements (free edge, nail body) and non-visible elements (root, nail bed, nail matrix, eponychium, and lateral nail folds).