CHAPTER 3 Physiology and Histology of the Skin

Vocabulary flashcards covering key concepts, structures, and terms from CHAPTER 3: Physiology and Histology of the Skin.

Integumentary system

The skin; the largest organ, acting as a protective barrier and containing skin layers, nerves, hair follicles, and glands.

Epidermis

The outermost layer of the skin composed of five strata; contains keratinocytes, melanocytes, Langerhans cells, and Merkel cells.

Stratum corneum

The horny, outermost epidermal layer; made of dead keratinocytes; waterproof barrier that regenerates and desquamates.

Stratum lucidum

Thin, clear layer found only in thick skin (palms and soles).

Stratum granulosum

Granular layer where keratinization and lipid production occur; desmosomes dissolve here as cells move up.

Stratum spinosum

Spiny layer where cells divide and enzymes produce lipids and proteins; contains Langerhans cells and melanosomes.

Stratum germinativum (basal layer)

Deepest epidermal layer where mitosis occurs; contains stem cells, keratinocytes, melanocytes, and Merkel cells.

Keratinocytes

Majority of epidermal cells (about 95%); produce keratin and lipids and form the epidermal barrier.

Melanocytes

Pigment-producing cells in the basal layer; produce melanin and transfer pigment via melanosomes.

Melanosomes

Pigment-containing organelles produced by melanocytes; transfer melanin to keratinocytes.

Tyrosinase

Enzyme that stimulates melanocytes to produce melanin.

Dermal–epidermal junction (DEJ)

The junction between the dermis and epidermis providing adhesion and strength.

Dermis

True skin; thick connective tissue layer containing collagen and elastin; houses vessels, nerves, glands, and follicles.

Papillary layer

Superficial dermal layer with dermal papillae; nourishes epidermis and contains touch receptors and capillaries.

Reticular layer

Deeper dermal layer rich in collagen and elastin; damage here leads to sagging and wrinkles.

Collagen

Protein providing skin strength and wound healing; makes up about 70% of the dermis; produced by fibroblasts.

Elastin

Fibrous protein imparting elasticity to the skin; present in smaller amounts and declines with age.

Glycosaminoglycans (GAGs)

Water-binding polysaccharides in the dermis that help maintain moisture and support collagen/elastin.

Hyaluronic acid

A key hydrating GAG in the dermis that helps retain moisture and support skin structure.

Extracellular matrix (ECM)

Network of collagen, proteins, and GAGs between cells that supports skin structure and metabolism.

Hypodermis (subcutaneous layer)

Deepest skin layer, largely adipose tissue (about 80% fat); cushions and stores energy.

Hair follicle

Appendage of the skin from which hair grows; associated with arrector pili, sebaceous glands, and hair shaft.

Hair shaft

Part of the hair that protrudes above the skin surface.

Arrector pili muscle

Small muscles that contract to cause goosebumps, helping with warmth.

Sebaceous glands

Oil glands connected to hair follicles; secrete sebum to lubricate skin and hair; clogged ducts form comedones.

Sudoriferous glands

Sweat glands; regulate temperature and excrete waste; two types: eccrine and apocrine.

Eccrine glands

Widely distributed sweat glands that open directly to the skin surface; main role in cooling.

Apocrine glands

Sweat glands associated with hair follicles (armpits, groin); secretions can cause odor when bacteria act on them.

Trans-epidermal water loss (TEWL)

Water loss through the skin; barrier function limits TEWL to protect hydration.

Acid mantle

Protective film on the skin surface formed by sebum, lipids, sweat, and water; typical pH ~5.5.

pH 5.5

The balanced, slightly acidic skin pH that helps protect against pathogens and regulate enzymes.

Desquamation

Shedding of stratum corneum cells; part of the normal cell turnover process.

Cell turnover

Rate at which skin cells are replaced; about 28 days in adults; faster in infants, slower with age.

Nerve receptors in the skin

Meissner’s corpuscles (light touch), Pacinian corpuscles (deep pressure), Krause end bulbs (cold), Merkel’s discs (touch), Ruffini endings (touch/pressure), free nerve endings (pain/temperature).

Sensation (in skin)

The skin’s ability to sense touch, heat, cold, pain, and pressure via nerve receptors.

Protection (skin function)

Skin acts as a barrier against external factors and microorganisms; sebum and the acid mantle contribute.

Heat regulation

Thermoregulation via evaporation, perspiration, radiation, insulation; vasodilation/constriction; hair aids heat retention.

Absorption (skin)

Uptake of chemicals, moisture, and oxygen through the skin; routes include intercellular, intracellular, and transappendageal.

Absorption routes

Intercellular (between cells), intracellular (through cells), and transappendageal (via hair follicles and glands).

Melanin

Pigment produced by melanocytes that protects skin from UV radiation; color varies with distribution.

Melanocytes

Pigment-producing cells in the epidermis that create melanin and melanosomes.

Melanosomes

Pigment-containing organelles that transfer melanin to keratinocytes.

Pheomelanin

Red-to-yellow melanin pigment.

Eumelanin

Dark brown-to-black melanin pigment.

UV radiation types

UVA (aging rays; deep penetration), UVB (burning rays; tanning; DNA damage), UVC (mostly blocked by ozone). HEV light (blue-violet) is a newer consideration for skin aging.

HEV light

High-energy visible light; may penetrate deeper than some UV rays and affect collagen, elastin, and pigmentation.

Free radicals

Unstable molecules with unpaired electrons; can damage cells; produced by UV and environmental stress.

Antioxidants

Molecules that donate electrons to stabilize free radicals and prevent cellular damage.

Glycation

Non-enzymatic bonding of sugar to proteins (e.g., collagen), forming advanced glycation end products that stiffen tissue and accelerate aging.

Estrogen

Primary female hormone; anti-inflammatory and antioxidant; supports skin moisture and tissue repair; declines with menopause.

Testosterone

Male hormone; can increase sebum production and influence hair growth and pore size.

Langerhans cells

Immune cells in the epidermis that process antigens and trigger immune responses; work with T cells and leukocytes.

Leukocytes

White blood cells that defend against infections and participate in immune responses.

T cells

Lymphocytes matured in the thymus; attack virus-infected or cancerous cells and help coordinate immune responses.

Lymph

Clear body fluid that nourishes skin cells, removes toxins, and participates in immune function.

Vitamin D synthesis

Skin-produced vitamin D in response to sun exposure, important for bone and immune health.

Nails (appendage)

Hard keratin plate protecting fingers and toes; onyx is the technical term for the nail.

Nail plate

Hard keratin plate that forms the visible part of the nail.

Lunula

Whitish half-moon area at the base of the nail plate.

Hyponychium

Area under the free edge of the nail at the fingertip; border between nail plate and skin.

Keratin

Fibrous protein providing resilience; found in hair, nails, and epidermis.

Keratinocytes vs keratin

Keratinocytes are epidermal cells that produce keratin; keratin is the protein that provides protection and structure.