MCB 244: Integumentary System

Stratum Granulosum

"Grainy layer" - 3-5 layers of keratinocytes producing keratin fibers (structural component of hair/nails), kartohyaline granules (promotes dehydration of cells & cross-linking of keratin fibers), & lamellated granules -No cell division, nuclei/organelles begin to disintegrate

Stratum Spinosum

"Spiny Layer" - 8-10 layers of keratinocytes bound by desmosomes -cells shrink until cytoskeletons stick out (spiny) -continue to divide, > thickness of epithelium -contain numerous dendritic (langerhans) cells (antigen-presenting immune cells)

Stratum Lucidum

"clear layer" (only in thick skin) -flat packed keratin-filled keratinocytes -glassy covering to stratum granulosum

Stratum Corneum

"horn layer" - 15-30 layers of dead keratinocytes that have been keratinized (cornified); replaced every 2 weeks. -soft keratin fibers glued in parallel arrays by karatohyaline -Extracellular space filled w/glycolipids from lamellated granule (form water barrier) -cornified: water/chemical resistant (not waterproof - interstital fluid can evaporate

Stratum Basale

-"Germinative layer" - many germinative (stem) or basal cells -attached to basal lamina by hemidesmosomes (strong bond b/w epidermis & dermis) -cells: basal cells, melanocytes (melanin), some Merkel cells in hairless skin (touch receptors) -Structures: A. Epidermal ridges (fingerprints) B. Dermal papillae (tiny mounds): > area of basal lamina, strengthen attachment b/w dermis/epidermis

Burns

-1st degree: damage to surface epidermis; heals on own -2nd degree: damage to epidermis & superficial dermis; heals on own. -3rd degree: damage to whole cutaneous layer, granulation tissue can't form thus no healing (requires skin grafts) -Burns >20% can be fatal -Affects: fluid/electrolyte balance, thermoregulation, protection from infection.

Control of Glands

-Autonomic Nervous System (ANS): control sebaceous & apocrine sweat glands, works simultaneously over entire body (no local control) -Merocrine Sweat glands: controlled independently: can be turned on/off in local regions in response to temp./emotions (sweating occurs locally) -Thermoregulation: main function of sesnible perspiration, works w/cardio. system to regulate body temp.

Epidermis

-Avascular stratified squamous epithelium -Nutrients/oxygen diffuse from capillaries in dermis -Keratinocytes: contain large amount of keratin (most abundant cell type in epidermis) -Thin Skin: hairy; covers most of body, 4 strata of keratinocytes -Thick Skin: no hair, covers palms & soles of feat, 5 strata of kratinocytes -Water resistant, not waterproof ; water from interstitial fluids evaporate -not seen or felt-500 ml/day (INSENSIBLE PERSPIRATION) -SENSIBLE PERSPIRATION - aware of water lose, active sweat glands

Lines of Cleavage in Dermis

-Collagen/elastic fibers in dermis are arranged in parallel bundles that resist force in a specific direction -important patterns: a parallel cut that remains shut will heal well; a cut across (right angle) pulls open & scars b/c it severs elastic fibers

Freckles, Vitiligo, & UV exposure

-Freckles: overproduction of melanin from single melanocyte. -Vitiligo: loss of melanocytes, likely result of auto-immune disorder -UV exposure: some need for vit. D production; over exposure harms fibroblasts (impaired maintenance of dermis -wrinkle) & chromosomes (cancer)

Hair Follicle Structure

-Glassy Membrane: thick basal lamina b/w epithelial follicle & con. tissue dermis -Hair Bulb: consists of epithelia; expanded base of follicle that surrounds papilla & matrix -Hair Matrix: dividing epithelial/basal cells & melanocytes above papilla that form new hair; cells gradually push toward surface -Hair Papilla: con. tissue @ base of bulb, contains capillaries & nerves; supports matrix

Hair Strucure

-Hair Root: embedded in dermis, not yet full formed, contains live cells. -Hair shaft: poke through epidermis, full organized dead hair 3 Layers: 1. Cuticle: outermost, overlapping dead keratinized cells form shiny surface. 2. Cortex: middle layer, dead cells contain hard keratin to provide stiffness 3. Medulla: core, dead cells contain soft keratin and air to provide flexibility

Structures of Hair Follicle

-Hair follicle -glassy membrane -hair bulb -hair papilla -hair matrix Accessory Structures: -Arrector pili: involuntary smooth muscle that causes hair to stand up ("goose bumps") -Sebaceous glands: lubricate hair & control bacteria

Dermis

-Location: b/w epidermis & subcutaneous layer -Function: anchors epidermal accessory structures -Contains: all cells of con. tissue proper, blood vessels, lymphatic vessels, nerves, & sensory receptors 2 layers: outer PAPILLARY layer & deep RETICULAR layer.

Hair Follicle

-Produced by tube of stratified squamous epithelium anchored in dermis -surrounds, supports, & makes hair -2 layers: INTERNAL ROOT SHEATH (contacts hair) & EXTERNAL ROOT SHEATH (contacts glassy membrane)

Functions of Integumentary System

-Protect: underlying organs/tissues -Excrete: salts, water, & organic wastes -Maintains: body temp. -Synthesize: Vitamin D3 -Store: lipids -Detect: sensory modulates -connected to circulatory & nervous system

Inner Reticular Layer

-Thick (80% of dermis) -Consists of: dense irregular con. tissue w/elastic & collagen fibers, blood & lymph. vessels, sensory nerves -function provide strength/flexibility; carry blood supply up from subcutaneous layer to papillary layer

Outer Papillary Layer

-Thin (20% of dermis) -Consists of: areolar con. tissue, comprise dermal papillae, capillaries, lymph. & sensory neurons -function: FEED dermis

Dermis Blood Supply

-arteries lie in hypodermis and extend through dermis -CUTANEOUS PLEXUS: network of arteries beneath reticular layer in hypodermis -SUBPAPILLARY PLEXUS: capillary network that provides blood to capillary loops following epidermal-dermal boundary -VENOUS PLEXUS: capillary return deep in subpapillary plexus -CONTUSION: bruise/trauma that ruptures blood vessels but doesn't break skin

Vitamin D3 production

-epidermal cells (spinosum & basale) produce CHOLECALCIFEROL - vit. D via intrxn. b/w UV & cholesterol-like steroid. -liver converts vit. D into hormone calcitriol (necessary to signal small intestine to absorb calcium/phosophorus -insufficient vit. D - Rickets (fed. law in US to include vit. D in milk)

Apocrine Sweat Glands

-found in armpits, around nipples, groin (after puberty) -secrete products into hair follicles (via MEROCRINE secretions) -produce sticky, cloudy secretions (sensible perspiration+protein+lipid) -microbes eat it-> wastes=body odor -surrounded by myoepithelial cells (squeeze apocrine gland secretions onto hair, respond to hormonal/nervous signals)

Mammary Glands

-integumentary gland -anatomically related to "apocrine" sweat glands -produce milk

Ceruminous Glands

-integumentary gland -modified sweat glands in passageway of external ear -produce CERUMEN (earwax) -Protect the eardrum by trapping particles

Integument

-largest organ system in body, 16% of weight. -2 parts: 1. Cutaneous membrane (skin: epidermis + dermis) 2. Accessory structures (e.g hair nails) originate in dermis, extend through epidermis

Hypodermis (subcutaneous layer)

-lies below integument -stabilizes position of the skin relative to muscles to permit independent movement of each -elastic areolar & adipose tissue -tightly interwoven w/reticular layer by con. tissue fibers -few capillaries -Subcutaneous fat (80% of all body fat) -distribution determined by hormones (children: even layer; males: abdomen, lower back, neck, arms;females: breast, buttocks, hips, thighs

Repair of Integument

-mesenchymal cells of dermis can regenerate connective tissue; basal cells of epidermis can regenerate epidermal tissue 1. Bleeding occurs 2. Mast cells trigger inflammatory response 3. scab stabilizes & protects the area 4.germinative cells migrate around the wound 5. macrophages clean the area 6. fibroblasts & endothelial cells move in, producing GRANULATION TISSUE 7. Fibroblasts produce scar tissue (inflammation <, clot disintegrates, a raised KELOID may form)

Epidermal Growth Factor (EGF)

-powerful peptide growth factor produced by glands (salivary, duodenum) & used to grow SKIN GRAFTS -Functions: promote division of basal cells, > keratin production, stimulate epidermal repair & glandular secretion

Finger/Toe Nails

-scale like projections on dorsal surface of distal digits -function: protect tips from mechanical stress, assist in gripping -consists of dead cells containing hard keratin -New nail formed at nail rood (epidermal origin - "dives" into dermis) -cuticle = stratum corneum

Alopecia

-shift from terminal to vellus hair, thinning/balding, some expected w/age -temporary (permanent) can result from some medications, radiation, chemotherapy, chemicals, etc. -Male Pattern baldness: genetic alopecia, early age onset; duet to change in circulating levels of sex hormones

Merocrine Sweat Glands

-widely distributed on body surface (especially palms/soles) -coiled, tubular glands -discharge directly onto skin surface -produce sensible perspiration (99% water+electrolytes, organic nutrients antibiotic/antimicrobial agents) -functions: cool skin, excrete water (electrolytes, drugs), & flush microorganisms & harmful chemicals. -highly productive (up to 1 gal./hr)

Hair Growth Cycle

1. Active Phase: new hair added to hair root by dividing cells in hair matrix (weeks to years) 2. Regressive Phase: cells of hair matrix stop dividing; hair root, papilla separate loose hair (club hair) 3.Resting Phase: cells of hair matrix & hair follicle inactive (1-3 months) 4. New Active Phase: hair follicle produces new hair, pushes out old club hair Head hair: grows 2-5 yrs/.33 mm per day.; cells absorb nutrients (history of exposure) -length differences due to differences in time spent in active phase (eyebrows-few months, head-many years)

Dermal strength/elasticity

1. Collagen Fibers (strong, resists stretching but bends easily) 2. Elastic Fibers (permits stretching and recoil, limits collagen fiber flex. to prevent damage) -Skin Turgor: water content of skin -Wrinkles: < in elastin content, damage, etc.; caused by dehydration, age, hormone changes, UV exposure -Stretch Marks:dermis stretched beyond elastic capacity -Retin-A: drug; increases blood flow to dermis stimulating repair (brings more fibroblasts, other repair mechanisms to repair collagen/elastin)

Integumentary Accessory Structures

1. Hair 2. Sebaceous glands 3. Sweat glands 4. Nails -derived from embryonic epidermis -located in dermis, project through skin surface

Sebaceous Glands

1. Sebaceous glands associated w/ hair follicles (simple branched alveolar glands) 2.Sebaceous follicles, which are NOT associated w/hair follicles; discharge directly onto skin; lubricate/protect epidermis, inhibit bacteria growth, prevent evaporation -active in fetus, turn off until puberty, & back on rest of adult life -acne: inflammation of sebaceous gland, usually due to bacterial infection/clogged pores.

Effects of Aging on Integument

1. Stem Cells activity < (skin thins) 2. Langerhans cells < (< immune response) 3. Vitamin D production < (brittle bones) 4. Glandular activity < (skin dry, body overheat) 5. Melanocyte activity < (become more pale, sensitive to sun) 6.Dermal blood supply < (feel cold) 7. Hair follicles die (terminal to vellus) 8.Dermis thins, less elastic (wrinkles) 9. Sex characteristics fade (fat deposits spread out) 10. Skin Repair slows

Layers of Epidermis

1. Stratum basale 2. Stratum spinosum 3. Stratum granulosum 4.Stratum lucidum (only thick skin) 5. Stratum corneum -cells divide, grow in stratum basale -it takes 7 to 10 days to migrate from basale to corneum (cells remain in corneum for to weeks before being shed)

Exocrine glands in Skin

1.Sebaceous glands (oil) -holocrine glands (destroy cell), secrete sebum onto hair follicle/skin via duct 2. Sweat Glands A. Apocrine glands (release onto hair follicles); constitutes body odor-pubic, underarm regions B. Merocrine (eccrine) glands (release onto skin)

Body Hairs

2.5 mil. hairs on body (25% on head) -everywhere except palms, soles, lips, certain areas of genitalia -Function: head (uv protection, cushion, insulation); nostrils, ear canals, eyelashes (guard openings to particles, insects); body hair (sense to very light touch)

Skin Color Influences

Dermal circulation (RBCs) & 2 epidermal pigments: Carotene & Melanin

Dermis nerves & sensory perception

Nerve fibers in skin control: blood flow, gland secretions, sensory receptors in dermis 1. Merkel Cells -deep layers of epidermis (superficial touch) 2. Free Nerve Endings -superficial dermis (pain & temp.) 3. Meissner's Corpuscles -superficial dermis (light touch) 4.Pacinian/Lamellated Corpuscles - deep dermis (reticular) (pressure & vibrations) -dermatitis: inflammation of skin (primarily papillary layer)

Capillaries & Skin Color

Oxygenated blood -Red color, hemoglobin in RBC, through skin = pink -Blood vessels dilate (vasodilation) -> skin reddens -Blood vessels constrict (vasoconstriction) -> skin pales -Cyanosis: bluish tint to skin, caused by severe < in blood flow/oxygenation; light interactions give deox. blood bluish skin tint _> low temp., heart failure, asthma

Hair Color

Ranges from yellow to black to melanin from melanocytes in hair matrix -melanin stored in cortex & medulla -hair dyes stain cortex & medulla, but damage cuticle -with age, melanin declines + air pockets in medulla > = white hair

Types of Hairs

Shape Determines Feel: -Round shaft: straight (Stiff) -Oval Shaft: wavy or curly -Flattened shaft: kinky 1. Vellus hairs: "peach fuzz"; lacks medulla, covers body (at puberty hormones can trigger switch to terminal hairs -pubic regions, armpits) 2. Terminal hairs - head, eyebrows/lashes: thick, coarse, pigmented

Melanocytes

location: stratum basale -synthesize melanin from tyrosine, packaged in melanosomes -melanosomes are transferred to cytoplasm of keratinocytes & cluster around top side of nucleus -eventually digested by lysosomes -protect skin from UV radiation -EVERYONE has ~1000 melanocytes per mm^2 (pale ppl= small melanosomes in stratum basale, spinosum; dark ppl. = larger, > numer of MELANOSOMES through stratum granulosum) -skin color depends on melanin production, not # of melanocytes (eumelanin-black/brown, pheomelanin-yellow/red) -

Carotene

orange-yellow, from diet -can be converted in vit. A -localized to epithelium -function: normal maintenance of epithelia (and eye photoreceptors -excess accumulates in stratum coreneum

Melanin

yellow-brown or black, produced from melanocytes in stratum basale -stored in melanosomes (transport vesicles) & transferred to keratinocytes -for UV protection in deeper layers (basal cells; no purpose in upper, dead layers