Chapter 06: The Integumentary System

Comprehensive vocabulary flashcards covering the anatomical structure, cellular composition, physiological functions, accessory organs, pigmentation, and clinical disorders of the integumentary system.

Dermatology

The scientific study and medical treatment of the integumentary system.

Integumentary system

The organ system consisting of the skin, hair, nails, and cutaneous glands.

Epidermis

The superficial layer of the skin composed of keratinized stratified squamous epithelium; it is avascular and relies on nutrient diffusion from the dermis.

Dermis

The deeper connective tissue layer of the skin beneath the epidermis, composed mainly of collagen and well supplied with blood vessels, cutaneous glands, and nerve endings.

Hypodermis

The layer of subcutaneous connective tissue beneath the dermis that contains abundant areolar and adipose tissue, binding the skin to underlying tissues and serving as an energy reservoir.

Thick skin

Skin covering the palms, soles, and surfaces of the fingers and toes; characterized by an epidermis about $0.5\,\text{mm}$ thick with a prominent stratum corneum, possessing sweat glands but lacking hair follicles and sebaceous glands.

Thin skin

Skin covering most of the body with an epidermis about $0.1\,\text{mm}$ thick; possesses hair follicles, sebaceous glands, and sweat glands.

Keratinocytes

The great majority of epidermal cells, responsible for synthesizing the tough, protective fibrous protein keratin.

Epidermal stem cells

Undifferentiated cells located exclusively in the deepest layer of the epidermis (stratum basale) that divide and give rise to keratinocytes.

Melanocytes

Cells located only in the stratum basale that synthesize the pigment melanin and distribute it via melanosomes to shield keratinocyte DNA from ultraviolet radiation.

Tactile cells

Touch receptor cells found in the basal layer of the epidermis that are associated with underlying dermal nerve fibers.

Tactile disc

The collective term for a single epidermal tactile cell and its associated sensory nerve fiber.

Dendritic cells

Phagocytic immune cells found in the stratum spinosum and stratum granulosum that guard against toxins and microbes.

Stratum basale

A single layer of stem cells and keratinocytes resting on the basement membrane at the base of the epidermis, also housing melanocytes and tactile cells.

Stratum spinosum

An epidermal layer composed of several layers of living keratinocytes firmly attached by desmosomes and tight junctions, named for their spiny histological appearance.

Stratum granulosum

An epidermal layer consisting of three to five layers of flat, living keratinocytes characterized by prominent, dark-staining keratohyalin granules.

Stratum lucidum

A thin, translucent epidermal layer found only in thick skin, where keratinocytes are densely packed with the clear protein eleidin.

Stratum corneum

The outermost epidermal zone consisting of up to $30$ layers of dead, scaly, keratinized cells that resist abrasion, penetration, and water loss.

Filaggrin

A protein released by keratohyalin granules in the stratum granulosum that binds keratin filaments into tough bundles.

Epidermal water barrier

A physiological barrier formed in the stratum granulosum by tight junctions and a secreted lipid mixture from membrane-coating vesicles, preventing systemic dehydration.

Dermal papillae

Upward, finger-like extensions of the dermis that interlock with the epidermal ridges to prevent epidermal slipping.

Epidermal ridges

Downward, wave-like projections of the epidermis that interlock with the underlying dermal papillae.

Papillary layer

The thin, superficial zone of the dermis composed of areolar connective tissue that allows leukocyte mobility and contains abundant small blood vessels.

Reticular layer

The deeper, thicker layer of the dermis composed of dense irregular connective tissue with thick bundles of collagen.

Striae

Stretch marks formed by tears in the dermal collagen fibers due to excessive stretching of the skin during pregnancy or obesity.

Autograft

A skin graft of tissue taken from another location on the same patient's body.

Allograft

A skin graft taken from an unrelated person, usually obtained from a deceased donor.

Eumelanin

The form of melanin that produces brown and black pigments in the skin and hair.

Pheomelanin

A sulfur-containing melanin pigment responsible for reddish to yellowish tones in hair and skin.

Cyanosis

An abnormal blue tint of the skin resulting from an oxygen deficiency in circulating blood.

Erythema

Abnormal redness of the skin caused by increased cutaneous blood flow (vasodilation).

Pallor

An abnormal pale or ashen skin tone caused by significantly reduced cutaneous blood flow.

Albinism

A genetic condition characterized by a lack of melanin synthesis, resulting in milky white skin and hair and pinkish eyes.

Jaundice

Yellowing of the skin and sclera caused by high levels of bilirubin in the blood, often indicative of liver dysfunction.

Hematoma

A bruise; a localized visible mass of clotted blood beneath the skin caused by trauma.

Friction ridges

Markings on fingertips formed during fetal development that enhance fingertip sensitivity, improve grip, and leave fingerprints.

Flexion lines

Creases on the flexor surfaces of digits, palms, wrists, and elbows marking locations where the skin folds during joint movements.

Hemangiomas

Birthmarks; patches of discolored skin caused by benign tumors of dermal capillaries.

Pilus

A hair; a slender filament of keratinized cells growing out of an oblique epidermal tube called a hair follicle.

Lanugo

Fine, downy, unpigmented hair that appears on the human fetus during the last 3 months of gestation.

Vellus hair

Fine, pale hair that replaces lanugo by the time of birth, constituting the majority of body hair in women and children.

Terminal hair

Longer, coarser, and heavily pigmented hair found on the scalp, eyebrows, and eyelashes, and forming pubic, axillary, and facial hair after puberty.

Hair bulb

The dilated swelling at the deep proximal end of a hair root in the dermis or hypodermis that caps the dermal papilla.

Hair matrix

A region of mitotically active cells directly above the dermal papilla that functions as the growth center of the hair.

Arrector muscle

A bundle of smooth muscle cells connecting the hair follicle to the dermal papillary layer; contraction pulls the hair upright (piloerection).

Anagen

The active growth stage of the hair cycle, lasting $6\text{ to }8\,\text{years}$ in scalp follicles, during which hair matrix cells actively divide and synthesize keratin.

Catagen

The transitional degeneration stage of the hair cycle, lasting $2\text{ to }3\,\text{weeks}$, during which mitosis ceases and the base of the hair hardens into a club hair.

Telogen

The resting phase of the hair cycle, lasting $1\text{ to }3\,\text{months}$, before the follicle re-enters anagen.

Alopecia

Thinning of the hair or baldness occurring across the scalp or body.

Hirsutism

Excessive or undesirable hairiness in areas not typically hairy, especially in women and children.

Vibrissae

Stiff guard hairs guarding the nostrils and auditory ear canals to block foreign particulate entry.

Nail plate

The hard, visible keratinized portion of the nail, composed of the free edge, nail body, and nail root.

Nail matrix

The mitotically active growth zone of thickened stratum basale at the proximal end of the nail bed.

Eponychium

The cuticle; a narrow band of dead epidermis that overhangs the proximal end of the nail plate.

Hyponychium

The epidermis of the nail bed lying beneath the nail plate.

Lunule

The opaque white crescent visible at the proximal border of a nail, caused by the thickness of the underlying nail matrix obscuring dermal capillaries.

Apocrine sweat glands

Sweat glands occurring in the groin, axillae, areolae, and male beard areas that empty into hair follicles, producing a thick, milky secretion containing fatty acids.

Eccrine sweat glands

Simple coiled tubular glands distributed widely across the body that secrete watery perspiration directly onto the skin surface for evaporative cooling.

Myoepithelial cells

Contractile epithelial cells present in apocrine and eccrine sweat glands that squeeze perspiration up into the duct in response to sympathetic stimulation.

Diaphoresis

Noticeable perspiration that visibly wets the skin, typically occurring in response to heat, physical exercise, or circulatory shock.

Cutaneous transpiration

Water loss that occurs via diffusion between epidermal keratinocytes and evaporation from the surface, independent of glandular sweat production.

Sebum

An oily secretion produced by holocrine sebaceous glands that lubricates and waterproofs the hair and stratum corneum.

Ceruminous glands

Modified apocrine glands located in the external auditory meatus that produce cerumen (earwax).

Basal cell carcinoma

The most common and least dangerous form of skin cancer, arising from the stratum basale and presenting as a small, shiny bump with a central depression and beaded edges.

Squamous cell carcinoma

A form of skin cancer arising from keratinocytes in the stratum spinosum, presenting as a raised, reddened, scaly lesion that may ulcerate and metastasize to lymph nodes.

Malignant melanoma

The most aggressive and lethal type of skin cancer, originating from melanocytes, characterized by asymmetry, irregular borders, and uneven pigmentation.

Eschar

The burned, dead necrotic tissue that forms following deep severe burns, which can cause severe toxic systemic effects and infection.

First-degree burn

A partial-thickness burn that involves only the epidermis, marked by redness, slight edema, and pain, typically healing within days.

Second-degree burn

A partial-thickness burn that damages the epidermis and part of the dermis, characterized by blistering, severe pain, and potential scar formation.

Third-degree burn

A full-thickness burn that completely destroys the epidermis, dermis, and often deeper subcutaneous tissues, requiring skin grafting, fluid replacement, and infection control.