Skin and Its Layers

Cards · 50

Integumentary system

The organ system comprising the skin, hair, nails, and glands that protects the body and helps maintain homeostasis.

Cutis (skin)

The body's largest organ, forming a protective outer barrier consisting primarily of the epidermis and dermis.

Epidermis

The outermost, avascular layer composed of stratified squamous keratinized epithelium; provides protection and prevents water loss.

Dermis

The vascular layer beneath the epidermis composed of connective tissue; supplies nutrients, provides strength, and houses sensory nerves.

Hypodermis (subcutis)

The subcutaneous layer beneath the dermis made of adipose and loose connective tissue; anchors skin, insulates, and stores energy.

Keratinocytes

The predominant epidermal cells that produce keratin, providing structural strength, waterproofing, and physical protection.

Melanocytes

Dendritic cells located in the stratum basale that synthesize melanin pigment to shield cell DNA from UV radiation damage.

Langerhans cells

Epidermal dendritic cells originating from bone marrow that detect antigens and trigger adaptive immune responses.

Merkel cells

Specialized mechanoreceptors in the stratum basale associated with nerve endings that detect light touch and shape.

Stratum basale (germinativum)

Deepest epidermal layer of single-row stem cells undergoing continuous mitosis to generate new keratinocytes.

Stratum spinosum

Epidermal layer of polyhedral keratinocytes joined by prominent desmosomes; provides mechanical strength and holds Langerhans cells.

Stratum granulosum

Layer of flattened keratinocytes containing keratohyalin and lamellar granules; forms the primary lipid-based water barrier.

Stratum lucidum

Clear, thin layer of dead, translucent keratinocytes found exclusively in thick skin such as the palms and soles.

Stratum corneum

Outermost layer of flattened, anucleated, dead corneocytes embedded in lipids; provides the final physical and chemical shield.

Corneocytes

Dead, fully keratinized terminal cells of the stratum corneum that resist friction, microbial invasion, and dehydration.

Desquamation

The enzymatic shedding of outer corneocytes from the stratum corneum, continuously renewing the epidermal surface.

Keratohyalin granules

Protein granules in the stratum granulosum containing profillaggrin, which aggregates keratin filaments into tight bundles.

Lamellar bodies

Secretory organelles in keratinocytes that release lipids into extracellular spaces to establish the epidermal water barrier.

Thick skin

Skin found on palms and soles containing all five epidermal strata, a prominent stratum lucidum, and no hair follicles.

Thin skin

Skin covering most of the body containing four epidermal strata, lacking stratum lucidum, and bearing hair follicles.

Dermal-epidermal junction

The basement membrane zone connecting the epidermis and dermis; anchors tissues and controls molecular exchange.

Dermal papillae

Finger-like projections of the papillary dermis into the epidermis that increase surface area for adhesion and nourish the epidermis.

Rete ridges

Downwards epidermal projections interdigitating with dermal papillae to resist shear stress and prevent skin tearing.

Papillary dermis

Superficial layer of the dermis composed of loose areolar connective tissue, fine collagen, capillary loops, and sensory receptors.

Reticular dermis

Deeper dermal layer composed of dense irregular connective tissue; provides tensile strength, resilience, and elasticity.

Fibroblasts

Primary cells of the dermis responsible for synthesizing collagen, elastin, and the extracellular matrix ground substance.

Collagen fibers

Abundant dermal fibrous proteins (primarily types I and III) that supply high tensile strength and structural support.

Elastic fibers

Protein fibers composed of elastin and fibrillin that allow skin to stretch and recoil back to its original shape.

Extracellular matrix (ECM)

Gel-like ground substance rich in hyaluronic acid and proteoglycans that cushions structures and retains dermal moisture.

Dermal macrophages

Phagocytic immune cells in the dermis that clear debris, ingest microbes, and assist in tissue remodeling and repair.

Mast cells

Dermal immune cells releasing histamine and inflammatory mediators during allergic reactions and pathogen defense.

Adipocytes

Lipid-storing cells constituting the hypodermis; provide thermal insulation, mechanical shock absorption, and calorie reserve.

Hair follicle

An epidermal invagination extending into the dermis that produces hair shafts and houses epithelial stem cells.

Arrector pili muscle

Smooth muscle bundle attached to hair follicles; contracts under sympathetic stimuli to cause piloerection (goosebumps).

Sebaceous glands

Holocrine glands linked to hair follicles that secrete oily sebum to lubricate and waterproof hair and epidermal surfaces.

Eccrine sweat glands

Merocrine coiled tubular glands distributed widely across the body that secrete hypotonic watery sweat for thermoregulation.

Apocrine sweat glands

Glands located in axillary and anogenital regions releasing viscous, protein-rich secretions metabolized by skin flora into odor.

Meissner's corpuscles

Encapsulated mechanoreceptors in dermal papillae that detect light touch, low-frequency vibrations, and texture changes.

Pacinian corpuscles

Large, layered lamellar mechanoreceptors in the deep dermis and hypodermis responsive to deep pressure and rapid vibration.

Ruffini endings

Spindle-shaped mechanoreceptors embedded in the reticular dermis that sense sustained pressure, skin stretch, and finger position.

Free nerve endings

Unencapsulated sensory dendrites extending into the epidermis that perceive pain (nociception), temperature, and itching.

Skin thermoregulation

Regulation of body temperature via dermal vasodilation/vasoconstriction and evaporative cooling through eccrine perspiration.

Melanin

Biochemical pigment (eumelanin and pheomelanin) transferring to keratinocytes to absorb UV rays and dictate skin color.

Vitamin D synthesis

Photochemical conversion of 7-dehydrocholesterol to cholecalciferol (vitamin D3) in epidermal cells triggered by UVB light.

Acid mantle

A slightly acidic surface film (pH 4.5-5.5) of sebum, sweat, and amino acids that inhibits colonization by pathogenic microbes.

Skin microbiome

Diverse commensal bacteria, fungi, and viruses occupying the stratum corneum that outcompete pathogens and modulate immunity.

Skin microcirculation

Subpapillary and cutaneous vascular plexuses that supply oxygen and nutrients while diverting blood flow for temperature control.

Langer's lines (cleavage lines)

Topological map lines indicating the predominant orientation of collagen fiber bundles throughout the reticular dermis.

Epidermal wound healing

Repair process involving keratinocyte detachment, migration across the defect, and mitosis to restore a stratified barrier.

Dermal wound healing

Multiphase repair involving hemostasis, inflammation, fibroblast proliferation with granulation tissue, and collagen remodeling.