integumentery system

Functions of the skin

Protection against mechanical damage and pathogens, thermoregulation, cutaneous sensation, metabolic secretion, synthesis of vitamin D, and prevention of dehydration.

Epidermis

The superficial, non-vascular layer of skin composed mostly of keratinized stratified squamous epithelium.

Stratum Basale

The deepest layer of the epidermis consisting of a single row of stem cells that undergo rapid division, as well as melanocytes.

Stratum Spinosum

The layer of the epidermis several cells thick where keratinocytes appear spiky and begin accumulating pre-keratin filaments.

Stratum Granulosum

The middle epidermal layer where keratinization begins, cells flatten, and organelles deteriorate as lamellar granules release lipids.

Stratum Lucidum

A clear, thin layer of dead keratinocytes found exclusively in the thick skin of fingertips, palms, and soles.

Stratum Corneum

The outermost epidermal layer consisting of dead, fully keratinized cells that act as a durable physical barrier.

Keratin

A tough, fibrous protective protein found in skin cells, hair, and nails that provides structural strength and water resistance.

Melanocytes

Specialized epidermal cells in the deepest layer that synthesize dark pigment in response to UV radiation.

Melanin

The pigment responsible for skin, hair, and eye color that forms a protective shield over cell nuclei against radiation damage.

UV radiation

Ultraviolet light energy from the sun that stimulates pigment production in skin cells but causes DNA damage if overexposed.

Dermis

The thick, vascular layer of skin beneath the epidermis composed of strong connective tissue, nerve endings, hair follicles, and glands.

Papillary layer

The superficial region of the dermis composed of loose connective tissue containing capillaries and sensory tactile receptors.

Dermal papillae

Finger-like projections of the dermis extending into the epidermis that form friction ridges and supply nutrients.

Collagen

The primary structural protein in the dermis that provides high tensile strength, firmness, and hydration.

Hypodermis / Subcutaneous Tissue

The tissue layer beneath the dermis consisting mainly of adipose tissue that anchors skin, stores energy, and provides thermal insulation.

Sebaceous glands

Exocrine glands connected to hair follicles that produce an oily lipid substance to lubricate, soften, and waterproof skin and hair.

Eccrine glands

Abundant tubular sweat glands distributed across the body that secrete a watery fluid primary for thermoregulation.

Apocrine glands

Large sweat glands in axillary and anogenital regions that secrete a viscous, organic fluid into hair follicles during emotional stress or sexual arousal.

Secretion

The process by which skin glands produce and discharge substances like sweat, oil, and protective chemical barriers onto the surface.

Sensation

The capacity of specialized skin receptors to detect touch, pressure, temperature changes, and painful stimuli.

Hair shaft

The portion of a hair strand that extends beyond the surface of the skin.

Hair follicle

The invagination of the epidermis into the dermis that surrounds and anchors the growing hair root.

Hair bulb

The enlarged base at the bottom of a hair follicle containing actively dividing cells and blood vessels.

Hair cuticle

The outermost single layer of overlapping keratinized cells on a hair strand that provides luster and protection.

Functions of hair

Providing physical protection, insulation, sensory perception of light touch, and guarding body openings against foreign particles.

Nail body

The visible, hard, fully keratinized plate covering the dorsal tip of a finger or toe.

Nail matrix

The thick, actively growing region at the proximal end of the nail bed responsible for producing nail cells.

Lunula

The white, crescent-shaped region at the base of the nail plate overlying the thick active growth zone.

Eponychium / Cuticle

The narrow fold of stratum corneum projecting onto the proximal portion of the nail plate.

Proximal nail fold

The fold of skin extending over the base of the nail root that forms the cuticle border.

Functions of nails

Protecting distal digits from mechanical trauma, enhancing fine tactile sensitivity, and providing mechanical support for picking up small objects.