cards tissue ap skin

Cutaneous membrane

The skin, composed of the superficial epidermal layer and the deeper dermal layer.

Epidermis

The superficial, avascular layer of keratinized stratified squamous epithelium in the skin.

Dermis

The deeper layer of skin composed of connective tissue, located between the epidermis and hypodermis.

Epidermal accessory structures

Structures derived from the epidermis that extend into the dermis, including hair, nails, and multicellular exocrine glands.

Hypodermis

A subcutaneous layer deep to the dermis composed of loose connective and adipose tissue that insulates, absorbs shock, stores lipids, and anchors skin.

Functions of the integumentary system

Protection, waste excretion, thermoregulation, melanin and keratin production, synthesis of vitamin $D_3$, sensory perception, and hypodermal lipid storage.

Epidermal avascularity

The condition of having no direct blood supply, requiring cells to rely on nutrient diffusion from dermal capillaries.

Keratinocytes

The most abundant cell type in the epidermis that continuously forms, synthesizes tough protective protein, flattens, dies, and sheds.

Thin skin

Skin consisting of four epidermal layers that covers most of the body surface.

Thick skin

Skin consisting of five epidermal layers, found exclusively on the palms of the hands and soles of the feet.

Stratum basale

The deepest epidermal layer attached to the basement membrane via hemidesmosomes, housing stem cells, melanocytes, and tactile cells.

Stratum basale stem cells

Undifferentiated cells in the deepest epidermal layer that divide continuously to generate replacement keratinocytes.

Tactile (Merkel) cells

Specialized sensory cells located in the stratum basale that detect light touch.

Stratum spinosum

An epidermal layer consisting of several cell rows bound by desmosomes and tight junctions, containing immune defense cells.

Dendritic (Langerhans) cells

Specialized immune cells residing in the stratum spinosum that protect against pathogens and superficial epidermal cancers.

Stratum granulosum

An epidermal layer of $3$ to $5$ cell rows where organelles disintegrate, keratohyalin cross-links keratin, and lamellar granules release lipids.

Lamellar granules

Membrane-bound structures in the stratum granulosum that secrete lipids to form a water-resistant barrier.

Stratum lucidum

A thin, clear layer of flattened, dead keratinocytes present only in thick skin.

Stratum corneum

The most superficial layer composed of $15$ to $30$ rows of dead, keratinized, anucleate cells that continuously shed.

Keratinocyte transit time

The duration of approximately $15$ to $30\,\text{days}$ needed for a cell to travel from the basal layer to the outermost surface.

Insensible perspiration

Continuous, unperceived water evaporation through the skin of approximately $500\,\text{mL/day}$.

Sensible perspiration

Active fluid secretion produced by sweat glands to facilitate evaporative cooling during heat or physical exertion.

Melanin

A yellow-brown to black pigment packaged in melanosomes that absorbs ultraviolet radiation to protect keratinocyte DNA.

Effect of UV light on melanocyte activity

Increases pigment synthesis and melanosome transfer without altering the overall count of pigment-producing cells.

Carotene

An orange-yellow pigment stored in the stratum corneum and subcutaneous fat that the body can convert into vitamin A.

Hemoglobin influence on skin hue

Provides a bright red tint when fully oxygenated, causes skin paleness during reduced blood flow, and creates a bluish cyanotic tint when oxygen levels drop.

Hypodermis

A subcutaneous layer deep to the dermis composed of loose connective and adipose tissue that insulates, absorbs shock, stores lipids, and anchors skin.

Functions of the integumentary system

Protection, waste excretion, thermoregulation, melanin and keratin production, synthesis of vitamin $D_3$, sensory perception, and hypodermal lipid storage.

Epidermal avascularity

The condition of having no direct blood supply, requiring cells to rely on nutrient diffusion from dermal capillaries.

Keratinocytes

The most abundant cell type in the epidermis that continuously forms, synthesizes tough protective protein, flattens, dies, and sheds.

Thin skin

Skin consisting of four epidermal layers that covers most of the body surface.

Thick skin

Skin consisting of five epidermal layers, found exclusively on the palms of the hands and soles of the feet.

Stratum basale

The deepest epidermal layer attached to the basement membrane via hemidesmosomes, housing stem cells, melanocytes, and tactile cells.

Stratum basale stem cells

Undifferentiated cells in the deepest epidermal layer that divide continuously to generate replacement keratinocytes.

Tactile (Merkel) cells

Specialized sensory cells located in the stratum basale that detect light touch.

Stratum spinosum

An epidermal layer consisting of several cell rows bound by desmosomes and tight junctions, containing immune defense cells.

Dendritic (Langerhans) cells

Specialized immune cells residing in the stratum spinosum that protect against pathogens and superficial epidermal cancers.

Stratum granulosum

An epidermal layer of $3$ to $5$ cell rows where organelles disintegrate, keratohyalin cross-links keratin, and lamellar granules release lipids.

Lamellar granules

Membrane-bound structures in the stratum granulosum that secrete lipids to form a water-resistant barrier.

Stratum lucidum

A thin, clear layer of flattened, dead keratinocytes present only in thick skin.

Stratum corneum

The most superficial layer composed of $15$ to $30$ rows of dead, keratinized, anucleate cells that continuously shed.

Keratinocyte transit time

The duration of approximately $15$ to $30\,\text{days}$ needed for a cell to travel from the basal layer to the outermost surface.

Insensible perspiration

Continuous, unperceived water evaporation through the skin of approximately $500\,\text{mL/day}$.

Sensible perspiration

Active fluid secretion produced by sweat glands to facilitate evaporative cooling during heat or physical exertion.

Melanin

A yellow-brown to black pigment packaged in melanosomes that absorbs ultraviolet radiation to protect keratinocyte DNA.

Effect of UV light on melanocyte activity

Increases pigment synthesis and melanosome transfer without altering the overall count of pigment-producing cells.

Carotene

An orange-yellow pigment stored in the stratum corneum and subcutaneous fat that the body can convert into vitamin A.

Hemoglobin influence on skin hue

Provides a bright red tint when fully oxygenated, causes skin paleness during reduced blood flow, and creates a bluish cyanotic tint when oxygen levels drop.

Cyanosis

A bluish skin discoloration caused by severe reductions in blood flow or tissue oxygenation.

Cholecalciferol

Vitamin $D_3$, a molecule synthesized by epidermal cells upon exposure to ultraviolet radiation.

Calcitriol

The active hormone synthesized by the kidneys from calcidiol that enables calcium and phosphorus absorption in the digestive tract.

Rickets

A developmental bone disorder caused by a shortage of vitamin $D_3$ or calcium, leading to flexible and abnormally shaped bones.

Papillary layer of dermis

The superficial dermal region made of areolar connective tissue containing dermal papillae, capillaries, and sensory receptors.

Dermal papillae

Projections of the papillary dermis into the epidermis that form epidermal ridges and fingerprints.

Reticular layer of dermis

The deep dermal region consisting of dense irregular connective tissue with collagen and elastic fibers.

Meissner's (tactile) corpuscles

Sensory receptors located in the papillary dermis that detect light touch.

Pacinian (lamellar) corpuscles

Sensory receptors located in the reticular dermis and hypodermis that detect deep pressure and high-frequency vibration.

Hair follicle

An epidermal invagination extending into the dermis or hypodermis that produces and anchors a hair.

Arrector pili muscle

A bundle of smooth muscle attached to a hair follicle that contracts to pull the hair erect, generating goosebumps.

Hair papilla

A peg of vascularized connective tissue at the base of the hair bulb that supplies nutrients to growing hair cells.

Hair matrix

The actively dividing epithelial layer in the hair bulb that produces hair cells and receives melanin from melanocytes.

Vellus hair

Fine, soft, lightly pigmented hair covering much of the human body surface.

Terminal hair

Coarse, long, heavily pigmented hair located on the scalp, eyebrows, and pubic regions.

Sebaceous glands

Exocrine glands that secrete sebum into hair follicles or directly onto the skin to lubricate structures and inhibit microbes.

Sebum

An oily mixture of lipids that conditions skin, keeps hair shafts pliable, and suppresses bacterial growth.

Apocrine sweat glands

Exocrine glands in the axillae, groin, and areolae that secrete a cloudy, lipid-rich fluid into hair follicles, producing body odor upon bacterial breakdown.

Eccrine (merocrine) sweat glands

Widespread exocrine glands opening directly onto the skin surface that produce watery sweat for evaporative cooling and waste excretion.

Ceruminous glands

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