Integumentary System Terms

Arrector pili: Tiny smooth muscles attached to hair follicles that cause the hair to stand upright when activated, resulting in "goose bumps."

Dermal papilla: Fingerlike projections of dermal tissue into the epidermis.

Dermis: The layer of skin under the epidermis, composed of a thin superficial papillary region with areolar connective tissue, and a deep reticular region of dense irregular connective tissue.

Epidermis: The superficial layer of skin, composed of keratinized stratified squamous epithelium.

Free nerve endings: Sensory nerve fibers in the dermal papillae that detect pain, heat and cold.

Hair follicle: Tubelike invagination of the epidermis with outer and inner root sheaths from which hair grows.

Hair follicle receptor: Nerve receptors that detect hair movement. Also called hair root plexus.

Hair root: The part of a hair that is embedded in the hair follicle.

Hair shaft: The nongrowing portion of a hair, which protrudes from the skin.

Hypodermis: Subcutaneous tissue deep to the skin; consists of adipose and areolar connective tissue.

Keratinocytes: Epidermal cells that produce the protein keratin.

Langerhans cells: Phagocytic immune cells of the epidermis. Also called epidermal dendritic cells.

Meissner corpuscles: Oval receptors in the dermal papillae; responsible for fine discriminative touch. Also called tactile corpuscles.

Melanocytes: Cells deep in the epidermis that produce melanin pigments; branching cell processes transfer melanin granules to keratinocytes, resulting in pigmentation of the epidermis.

Merkel disc: A complex of an epidermal Merkel cell associated with a tactile sensory nerve ending that is responsible for light touch. Also called tactile discs.

Pacinian corpuscles: Oval receptors deep in the dermis, responsible for deep cutaneous pressure and vibration. Also called lamellar corpuscles.

Sebaceous glands: Exocrine glands in the dermis that usually open into hair follicles, and secrete oily sebum by a holocrine mechanism.

Stratum basale: Deepest layer of epidermis, composed of dividing stem cells.

Stratum corneum: Outer layer of epidermis, consisting of several layers of dead, flat, keratinized cells.

Stratum granulosum: A middle layer of epidermis, consisting of several layers of flattened cells with granules.

Stratum spinosum: A middle layer of epidermis, composed of keratinocytes.

Sudoriferous glands: Exocrine sweat glands in the dermis that secrete sweat by a merocrine mechanism.

Sweat glands, Apocrine: Sudoriferous glands that open into hair follicles, and develop during puberty in the axilla and pubis; they secrete a viscous milky sweat that supports bacteria growth, leading to body odor.

Sweat glands, Eccrine: Sudoriferous glands that open into pores at the surface of the skin, and found on almost all parts of the body; they secrete a watery sweat that cools the body.

Skin Burn Terms

First-degree burn: Superficial burn that damages only the epidermis.

Second-degree burn: Partial-thickness burn that damages the epidermis and upper region of the dermis, usually forming blisters.

Third-degree burn: Full-thickness burn that destroys all of the epidermis and dermis, may damage deeper tissue, and usually requires skin grafting.

Rule of Nines for Burns: Method of computing the severity of burns by dividing the body into a number of areas, each accounting for 9 % of the total area. Burns are considered critical if over 25% of the body has second-degree burns, or over 10% of the body has third-degree burns, or there are third-degree burns on the face, hands, or feet.

Skin Cancer Terms

Basal cell carcinoma: Most common and least harmful type of skin cancer, where stratum basale cells proliferate and invade the dermis and hypodermis, causing tissue destruction.

Squamous cell carcinoma: A type of skin cancer where keratinocytes of the stratum spinosum grow rapidly and may metastasize if not removed.

Melanoma: Most dangerous type of skin cancer, where melanocytes grow rapidly and often metastasize.

ABCD rules for skin cancer: Carcinoma may become fatal if any of the following conditions exist: A: Asymmetry; the two sides of the pigmented area do not match; B: Border is irregular and exhibits indentations; C: Color (pigmented area) is black, brown, tan, and sometimes red or blue; D: Diameter is larger than 6 mm (1/4 inch); E: Evolving or changing shape and size.