A&P: Integumentary System

Integument

Cutaneous membrane (skin) covering body and accessory structures (nails, hair, sweat glads, sebaceous glands); largest organ, comprised of epithelium, connective tissue, nerves

Barrier to outside world from trauma, harmful chemicals, pollutants, microbes, UV

Sensory inputs for touch, pressures, temperature, pain

Epidermis

Keratinized, stratified squamous epithelium with 4-5 strata (come lets get sun burned)

Stratum Basale (stratum germinativum, basal layer)

Deepest epidermal strata; single cuboidal to low columnar cell layer attached to basement membrane by hemidesmosomes

Contains large keratinocyte stem cells, melaoncytes, Merkel (tactile) cells

Keratinocytes

Synthesize keratin; migrate from stratum basale to stratum corneum

Week 1-2: migrate & keratinize

Week 3-4: protect & shed

Keratin

Protein for strength; fibrous molecules can twist & intertwine to form helical intermediate filaments of the cytoskeleton.

Cytokeratins found in keratinocytes provides strength, water resistance to skin

Melanocytes

Produce melanin via melanosome & store; transfer to surrounding stratum basale keratinocytes, sometimes other layers

Scattered in SB among keratinocytes

Melanin

Pigment produced by melanosomes; clusters around keratinocyte nucleus to provide UV protection

Black, brown (eumelanin); tan, yellow-brown (pheomelanin) colors

Merkel (tactile) cells

Sensitive to touch; release chemicals to stimulate sensory nerve endings when compressed

Scattered throughout SB, especially in sensitive areas such as fingertips

Stratum spinosum

Spiny layer; several layers of polygonal keratinocytes beginning to differentiate into nondividing, specialized keratinocyte attached by desmosomes

Also contain epidermal dendritic (Langerhans) cells

Epidermal dendritic cells (Langerhans)

Immune cells that hep fight infection in epidermis; present in stratum spinosum and granulosum

Phagocytosis initiates immune response to pathogens beyond superficial epidermis & cancer cells

Stratum granulosum

Granular layer; 3-5 layers keratinocytes; significant keratin synthesis, keratinization begins (granules are proteins to aggregate keratin filaments)

Keratinization

Process where keratinocytes synthesize significant amounts of keratin protein; accumulation causes disintegration of nucleus/organelles, cell death

Fully keratinized cells in superficial layers are structurally strong

Stratum lucidem

Thin translucent region 2-3 layerss thick only in thick skin of palms, soles; contain eleidin protein (intermediate product in keratin formation)

Stratum corneum

Superficial layer of epidermis of 20-30 layers of dead, scaly, interlocking fully keratinized/cornified cells (dead, anucleate)

Inhospitabel for microorganisms due to structure & demicidin (antimicrobial peptide in sweat)

Thick skin

All 5 layers, with no hair follicles, sebaceous glands

Palms & soles only

Thin skin

4 layers with hair follicles, sebaceous & sweat glasds

Skin color

Result of hemoglobin (red), eumelanin (black/brown), pheomelanin (tan/yellow/red), carotene (yellow-orange)

Exertion, genetics, UV exposure, diet

Albinism

Tyrosinase enzyme for melanin production nonfunctional

Nevus (mole)

Harmless melanocyte overgrowth; can become malignant due to UV exposure

Freckles

Yellow/brown spots; localized increase of melanocyte activity

UV exposure & heredity influence pigmentation

Hemangioma

Benign tumor due to blood vessel proliferation

Capillary hemangioma: straw-berry color birthmark in birth/childhood

Cavernous hemangioma: port-wine stain involve larger dermal vessels

Friction ridges

Patterns following contours of skin on palm, soles, fingers, toes

Increase friction, leave prints

Studied in dermatoglyphics

Dermis

.5mm-3mm layer of integument composed of CT proper; mainly collagen with some elastic & reticular fibers and motile dendritic cells

Also contains blood vessels, sweat glands, sebaceous glands, hair follicles, nail roots, sensory nerve endings, arrector pili

Papillary and reticular layers

Papillary Layer

Dermal Papillae

Reticular Layer

Lines of Cleavage

Stretch marks/Striae

Environmental Protection

Water Loss/Gain Protection

Vitamin D Synthesis

Calcitriol

Secretion

Absorption

Temperature regulation

Immune function

Sensory Reception

Tactile sensory receptor

Nail

Nail matrix

lunula

Nail fold

Eponychium

Cuticle

Hyponychium

Hair

Lanugo

Vellus

Terminal hair

Hair bulb

Hair papilla

Root

Shaft

Hair matrix

Medulla

Cortex

Cuticle

Hair follicle

Arrector pili

Protection

Heat retention

Sensory reception

Visual identification

Age, identity dermin

Anagen phase

Hair active growth phase

1.5-7years depending on genetics & body region

80%-95% follicles on scalp

Catagen phase

Cell division ceases and hair follicle undergoes involution for 3-4 weeks

Telogen phase

Resting phase where hair is usually shed; 3-4 months long and then the bulb starts regrowing

Sweat gland

Exocrine gland with coiled, tubular secretory portion and sweat gland duct; merocrine or apocrine

Sweat pore

Opening of sweat gland duct

Eccrine sweat gland (merocrine)

Simple coiled, tubular glands that discharge sweat directly onto skin by exocytosis; 99%water in secretion

Apocrine sweat gland

Coiled, tubular glands that release seat into hair follicles around axillae, nipples, pubic & anal regions

Produces viscous, cloudy sweat; contributes to body odor due to batera

Sebaceous gland

Holocrine glad producing sebum (oily, waxy secretion) usually discharged into hair folicle and onto hair to lube skin/hair and prevent bacterial growth

Become active largely in puberty due to sex hormones

Ceruminous gland

Modified apocrine sweat gland for cerumen (waterproof earwax) located in external acoustic meatus (ear canal)

Cerumen & hairs trap foreign particles, organisms, lubricate eardrum/canal

Mammary gland

Modified apocrine sweat gland for milk; becomes functional only in pregnant & lactating females initiated by gonadal and pituitary hormones

Regeneration

Damaged cells are replaced by cell division; possible when cells can divide and organ isn’t too badly damaged

Fibrosis

Scar tissue deposition during healing; binds damaged parts together with collagen fibers for structural but not functional restoration

Skin wound healing

Blood released into wound, brings clotting proteins, WBC

Clot forms for temporary barrier; macrophages, neutrophils clean wound

Granulation tissue forms deep in would; macrophages remove clotted blood, fibroblasts produce new collagen fibers

Epithelial regeneration & fibrosis

Periderm

Fetal squamous epithelium covering underlying basal layer by week 7; forms stratum basale

Vernix caseosa

Waterproof protective coating of sloughed periderm cells and sebum coating fetus skin

Hair buds

Immature hair follicle; appears at 9-12 weeks

Basal cell carcinoma

Most common skin cancer; least dangerous, low metastasis

Squamous cell carcinoma

Stratum spinosum keratinocyte origin; scaly lesion, can metastasize

Malignant melanoma

Most deadly skin cancer; melanocyte origin, manifested as changing mold