Integumentary System

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Epidermis

The superficial, avascular layer of skin composed of epithelial cells that serve as outermost protective layer of the body. (broken into 5 layers)

Dermis

The deeper layer of skin composed primarily of connective tissue; broken into 2 layers

Hypodermis

The subcutaneous layer deep to the dermis composed of adipose tissue that insulates the body, absorbs shock, and anchors skin to muscle.

Keratinocytes

The most abundant epidermal cells, responsible for producing a tough fibrous protein that provides physical protection and water resistance.

Melanocytes

Spider-shaped cells in the stratum basale that synthesize pigment granules to shield cell nuclei from ultraviolet radiation.

Langerhans cells

Macrophage-like dendritic cells that migrate from bone marrow to the stratum spinosum to engulf invaders and trigger immune responses.

Merkel cells

Tactile sensory cells located at the epidermal-dermal junction that detect light touch.

Stratum basale

The deepest layer of the epidermis consisting of a single row of mitotic stem cells continuously generating new cells.

Stratum spinosum

The epidermal layer above the basale where cells are anchored together by desmosomes, producing a spiny microscopic appearance.

Stratum granulosum

The epidermal stratum where cells begin producing keratohyalin granules and release lamellar bodies containing water-resistant lipids as they begin to die.

Stratum lucidum

A clear layer where cells begin to lose nuclei and die (along with dead keratinocytes); found exclusively in the thick skin of the palms and soles.

Stratum corneum

The outermost epidermal zone consisting of 20 to 30 layers of dead, anucleate, heavily keratinized cells that continuously flake off.

Dermal papillae

Fingerlike projections of the papillary dermis into the epidermis that strengthen the junction between layers and produce friction ridges (fingerprints).

Meissner's corpuscles

Encapsulated nerve endings located in dermal papillae that sense light touch and gentle pressure.

Pacinian corpuscles

Deep lamellated receptors situated in the reticular dermis and hypodermis that detect heavy pressure and vibrations.

Free nerve endings

Unencapsulated sensory receptors throughout the dermis that detect temperature, pain, itching, and tickling.

Arrector pili

Smooth muscle bundles attached to hair follicles that contract in response to cold or fear to pull hairs upright.

Rickets

A disease causing soft, weakened bones resulting from insufficient vitamin D synthesis and reduced calcium absorption.

Hair shaft

The portion of hair extending above the surface of the skin whose cross-sectional shape determines hair texture.

Hair follicle

Tunnel where the hair grows from

Vellus hair

Fine, unpigmented body hair commonly called peach fuzz found on children and across adult bodies.

Terminal hair

Coarse, darker hair found on the scalp, eyebrows, eyelashes, and axillary/pubic regions after puberty.

Nail matrix

The thickened proximal region of the nail bed responsible for generating new cells for nail elongation.

Lunula

The visible white crescent-shaped area at the base of the nail plate.

Eponychium

Also known as the cuticle; layer of clear skin along the bottom of a fingernail or toenail

Sebaceous glands

Holocrine exocrine glands attached to hair follicles that secrete an oily substance to lubricate hair, prevent dehydration, and kill bacteria.

Eccrine sweat glands

Widespread coiled tubular glands producing a watery secretion that prevents overheating via evaporative cooling.

Apocrine sweat glands

Axillary and anogenital glands activating at puberty that produce a viscous, lipid-rich secretion that bacteria break down into body odor.

Ceruminous glands

Modified apocrine sweat glands located in the external acoustic meatus that secrete earwax.

Nail plate

The visible, hard keratinized body of the digit covering the underlying soft tissue.

Nail bed

The pink-tinted, vascularized epithelial tissue situated directly beneath the hardened nail plate.

Free edge

The distal portion of the nail plate extending outward past the end of the digit.

Nail root

The proximal segment of the nail embedded deep within the skin fold.

Nail fold

The cutaneous folds overlapping the proximal and lateral borders of the nail plate.

Papillary layer

The superficial one-fifth of the dermis composed of areolar connective tissue with abundant capillary loops and sensory receptors.

Reticular layer

The deeper, thicker four-fifths of the dermis composed of dense irregular connective tissue providing cutaneous elasticity and strength.

Hair root

The lower portion of the hair structure anchored beneath the skin's surface within the follicle.

Sudoriferous glands

The general class of exocrine coiled tubular structures in the skin responsible for sweat secretion.

Mammary glands

Specialized modified apocrine exocrine organs that produce milk.

Sebum

An oily lipid mixture secreted by follicular glands that lubricates skin and exerts bactericidal effects.

Capillary loops

• where oxygen and nutrients are dropped off in the dermis

• where CO2 and waste are removed from the dermis

Acid mantle

A slightly acidic chemical barrier produced by skin secretions (sweat and sebum) that retards bacterial growth on the skin surface.