Chapter_5_Integumentary_System (1).pdf

Chapter 5: Integumentary System I. Introduction – Structure of the Skin a. Integument = epidermis (epithelial tissue) + dermis (connective tissue) + subcutaneous layer (Sub Q or hypodermis) i. Skin = epidermis + dermis 1. Largest organ of the body 2. Area = 2 m2 3. Thickness = 0.5 mm (eyelids) to gr...

Chapter 5: Integumentary System I. Introduction – Structure of the Skin a. Integument = epidermis (epithelial tissue) + dermis (connective tissue) + subcutaneous layer (Sub Q or hypodermis) i. Skin = epidermis + dermis 1. Largest organ of the body 2. Area = 2 m2 3. Thickness = 0.5 mm (eyelids) to greater than 4.0 mm (heel) b. Development of the Integument i. From the gastrula 1. Ectoderm epidermis 2. Mesoderm dermis + hypodermis c. Functions of the Skin/Integument i. Thermoregulation: sweat at surface & controlling flow of blood to the dermis. ii. Blood reservoir: 8-10% of total blood at rest iii. Protection: 1. produces keratin (from keratinocytes) to protect against microbes, abrasions, heat and chemicals 2. lipids (fats) – waterproofing, prevents dehydration 3. sebaceous glands – produce oils to prevent the skin from drying out and is a barrier to micrdobes 4. acidity (pH) from perspiration slows some microbes 5. melanin (from melanocytes) shields UV rays 6. intraepidermal macrophages – alerts immune system 7. dermal macrophages – phagocytose bacteria & viruses iv. Cutaneous sensations: touch – deep pressure & tickling/light touch, pain (tissue damage), temperature v. Excretion and absorption: 400mL of H2O evaporates daily, additional 200mL as sweat (sedentary), small amounts of salts, CO2, ammonia & urea; absorb fat soluble Vit (A,D,E,K), certain drugs, O2 & CO2. Topical steroids pass through easily – inhibit production of histamines by mast cells. vi. Synthesis of Vit D: requires UV light to activate precursor (10-15 min 2x’s/wk), then liver & kidney produces calcitriol (active hormone = Vit D which is used to absorb Ca2+ from foods in the GI tract) II. Epidermis a. Keratinized stratified squamous epithelium b. 4 cell types i. Keratinocytes (90%): tough, provides keratin for protection and lamellar granules (waterrepellant). ii. Melanocytes: cuboidal with projections to other cells, produces the pigment melanin (yellow-red or brown-black for skin color), absorbs UV light, hovers over nucleus to protect DNA (though melanin itself can be damaged by too much UV). iii. Intraepidermal macrophages (Langerhan’s cells): from red bone marrow, involved in immune response, easily managed by UV. iv. Tactile epithelial (Merkel) cells: deepest layer, contact flattened processes of sensory neuron, detecting touch sensation. c. 5 Layers of the Epidermis i. Stratum Basale (stratum germinativum – forms new cells) 1. Deepest layer 2. Single row of cuboidal or columnar keratinocytes (some of which are stem cells to produce new keratinocytes) a. Some melanocytes and tactile epithelial cells are scattered in the basal layer as well 3. Desmosomes: bind stratum basale cells together 4. Hemidesmosomes: bind stratum basale to basement membrane 5. Keratin: intermediate filaments form tough protein keratin (formed from keratinocytes), becomes more prominent in more superficial layers. ii. Stratum Spinosum (thornlike) 1. Numerous keratinocytes + a few tactile cells, intraepidermal macrophages & projections of melanocytes. 2. Same organelles 3. Begin to shrink and pull apart except at desmosomes (makes it look like thorns sticking out of cells) 4. Keratin intermediate filaments fill into the desmosomes iii. Stratum Granulosum (little grains) 1. Mid-epidermis 2. 3-5 layers of flattened keratinocytes undergoing apoptosis 3. Transitional layer from living to dead 4. Nuclei and organelles begin to degenerate (getting further from source of nutrition) 5. Keratin intermediate filaments no longer produced, but are more prominent as the become the only things left 6. Keratohyalin: assembles intermediate keratin filaments into keratin 7. Lamellar granules: release lipid rich secretions into superficial layers iv. Stratum Lucidum (lucid = clear) 1. Present only on thick skin (soles of feet, palms, finger tips) 2. 4-6 layers of clear, flat, dead keratinocytes 3. Provides toughness, arranged in more parallel structure v. Stratum Corneum (corne = horn/horny) 1. 25-30 layers of flattened, dead keratinocytes 2. Corneocytes or squames = packages of keratin a. No nuclei or any internal organs b. Overlap, forming jigsaw-like puzzle, strongly bound 3. Continuously shed and replaced by cells of deeper strata 4. Callus: abnormal thickening of stratus corneum over areas of high friction Mnemonic: make up your own! (something meaningful to you) deep to superficial: Baby Spits-up, Grandpa Loses Cool or Baby Sitters Get Lotsa Cash superficial to deep: Come, Let’s Get Some Beers! or Chris’ Legs Got Sun Burned Clinical Connection: Skin Grafts Useful when large areas of skin damaged: burns, injury, cancer Types o Autograph: taken from different part of same body o Isograph: taken from identicle twin o Autologous skin transplant: healthy skin of same person removed, grown in lab, then transplanted What is the anatomical reason for why they are needed? d. Growth of Epidermis i. Cells start as stratum basale (from surrounding stem cells) ii. Begin changing as they move toward the surface iii. Keratinization = accumulation of keratin (from/in keratinocytes) iv. Undergo apoptosis (planned cell death) v. Takes 4-6 wks (0.1 mm thickness) vi. Rate of cell division increases when injured vii. Hormones (epidermal growth factor) influence/play a roll in: 1. Dandruff = excessive amount of keratinized cells shedding III. a. b. c. d. Dermis Deeper layer of skin Thicker than epidermis Fixed fibroblasts, free/wandering macrophages, mast cells, eosinophis, neutrophils & dermal interstitial dendritic cells (immunity) 2 main regions i. Papillary region (papilla = nipple) 1. Superficial & thin 2. Thin collagen & fine elastic fiberes 3. Areolar CT 4. Dermal papilla = finger-like structures projecting up into the epidermis 5. Capillary loops = blood capillaries 6. Meissner corpuscles (corpuscles of touch) 7. Free nerve endings: warmth, coolness, pain, tickling (light touch) & itching ii. Reticular region (netlike) 1. Thick and deeper 2. Dense irregular CT, primarily collagen and elastin fibers a. Thick collagen fibers, scattered fibroblasts, wandering macrophages, some elastic fibers i. Collagen arranged in a netlike manner, aligned with tensile forces b. Knowledge of tension lines important for plastic surgeons (incisions to go with, not across, lines) 3. Blood vessels, nerves, hair follicles, sebaceous (oil) glands and sudoriferous (sweat) glands in between fibers iii. Epidermal ridges 1.Grooves and ridges of palms, fingers, soles & toes 2.Regions of the epidermis that project down into the dermis, between the dermal papillae 3.Produced during the 3rd month of fetal development (1st trimester) 4. Sweat glands on epidermal ridges produce oil fingerprints a. Genetically determined, but identical twins differ b. Remain constant throughout life, just get bigger 5. Fxnl: a. Increase surface area increased friction increased grip strength b. increased tactile sensitivity c. increased blood supply as source of nutrition for stratum basale in epidermis (no blood vessels) in epidermis d. Stronger bond b/n epidermis & dermis iv. Skin color 1. Determined by amount of melanin, hemoglobin and carotene (3 different pigments) 2. Amount of melanin pale yellow to reddish brown to black a. # melanocytes is the same in most people b. Differences are due to the amount of pigment produced 3. Freckles = areas of accumulation of melanin a. Light (ephelidiz) – light skinned people, inherited b. Dark (letigines) – sunburn freckles, over exposure to UV light i. Age spots / liver spots are a form of dark freckles c. Mole (nevus) – benign overgrowth of melanocytes 4. Albinism – inherited inability to produce melanin (can’t synthesize tyrosinase) a. Skin burns easily, may have difficulty with eyes. 5. Vitiligo – irregular white spots in patches where complete loss of melanocytes occur 6. Dark skinned individuals – increased melanin in epidermis 7. Light skinned individuals – decreased melanin, skin is white, pink, red (due to hemoglobin) 8. Carotene (precursor of Vit A) – stored in stratum corneum, fatty areas of dermis & Sub Q orange colored skin 9. Cyanosis (blue) – in nail beds, mucous membranes, & skin due to O2. 10. Jaundice (yellow) – buildup of yellow pigment bilirubin in skin & whites of eyes (liver diseased or not developed) 11. Erythema (red) – engorgement of capillaries 12. Pallor (paleness) – shock and anemia. Lack of blood supply. Lips have thin stratum corneum so loss of color easily seen. 13. Tattoos – injecting ink into the dermis. Permanent, though can stretch and fade (UV lymphatic flushing, scabs) over time. IV. Subcutaneous layer (Sub-Q) or Hypodermis a. Deep to the dermis b. Not part of the skin c. Varies greatly depending on the body part d. Fibers from the dermis extend to the hypodermis which then attaches to underlying fascia (CT of muscle & bone) e. Fat storage: from very thin to 4-6 inches thick f. Large blood vessels that supply/drain capillaries g. Lamellated (Pacinian) corpuscles: encapsulated nerve endings sensitive to pressure h. Fxn’s i. Loose binding tissue – unites upper layers of skin to deeper layers while letting it move freely ii. Tough fat pads (palms & soles) iii. Principle site of energy storage iv. Insulation layer V. Skin Cancer a. Main Types i. Basal cell carcinoma – 78% of all skin cancer, from stratum basale, rarely metastasizes ii. Squamous cell carcinoma – 20% of all skin cancer, from stratum spinosum, may metastasize due to pre-existing sun damage iii. Malignant melanoma – 2% of all skin cancer, (1 in 75, double what it was 15 years ago due to decreased ozone layer & spending more time in the sun [thinking protected by sunscreen]), can be deadly! b. ABCD risk signs of skin cancer i. A – asymmetry ii. B – border irregular iii. C – color uneven iv. D – diameter > 6mm VI. Accessory Sx’s of the Skin a. Hair (pili) i. 60/cm2 to 600/cm2, from a fraction of 1mm to > 1 m long, 0.005 – 0.6 mm thick ii. Absent in palms, palmar surface of fingers, plantar toes iii. Fxn’s 1. Protects head from UV rays; eyes, ears & nostrils from foreign particles 2. Reduces heat loss 3. Touch receptors activated with mvmt of hairs iv. Anatomy 1. Hair shaft a. Columns of dead keratinized epidermal cells b. Shape: round straight hair; oval wavy hair; kidney-shaped curly hair 2. Hair root a. 3 concentric layers that can penetrate the dermis and sometime sub-Q i. Medulla: inner most 2-3 rows of pigmented granules and air spaces ii. Cortex: middle, forms major part of shaft, pigment granules (mostly air spaces in gray hair, all air in white) iii. Cuticle: outer most single layer of keratinized cells 3. Hair follicle a. Surrounds root b. 2 layered sheath 4. Arrector pili – smooth muscle from superficial dermis to hair follicle a. Under stress/cold, arrector pili contracts, making hair perpendicular to skin, causing i. Goose bumps, trapping warm air ii. Intimidation to predators 5. Sebaceous (oil) glands – surround hair to keep it oiled (preventing brittle, cracking hair) 6. Dendrites of neurons forming hair root plexus – initiates nerve impulses due to stretching from movement v. Growth 1. Normally lose 70-100 hairs/day 2. Visible hair is dead: fully keratinized 3. 3 phases of growth a. Growth phase: 85% of the time, taking 2-6 years, rapid mitosis (affected by chemotherapy) i. Chemotherapy stops rapidly dividing cells in the hair matrix ii. The 15% that are in the resting phase remain and can regrow later. b. Regression: hair matrix stops dividing, hair follicle shrinks, takes 2-3 weeks c. Resting: 15% of the time (approx. 3 months), then hair falls out and cycle starts over b. Skin Glands i. Single of groups of epithelial cells that secrete a substance ii. Exocrine glands of the skin 1. Sebaceous (oil) glands a. Simple branched acinar (rounded) glands, cuboidal cells b. Connected to hair follicles c. Secreting portion in the dermis, b/n arrector pili & hair follicles i. In lips, glans penis, labia minor they secrete directly onto the surface of the skin d. Cuboidal cells divide, full up lumen, accumulated lipid filled vesicles and burst e. Fills duct with sebum (mix of fats, cholesterol, proteins & inorganic salts i. Prevents hair from becoming brittle & drying out ii. Prevents excessive evaporation of water from skin iii. Inhibits growth of bacteria f. Puberty: glands grow in size and amount of secretions (sebum) 2. Sudoriferous (sweat) glands a. Release secretions by exocytosis b. Empty secretions onto skin through pores or into hair follicles c. 2 types i. Eccrine/Merocrine sweat glands: foreheads, palms, soles of feet 1. Simple coiled tubular 2. Fxn by exocytosis of secretory vesicles containing sweat. 3. Most of body (not nail beds, lip margins, glans penis/clitoris, labia minora or eardrums) 4. Secreted in dermis through ducts that extend through epidermis to skin surface 5. Mostly H2O, some ions (Na+, Cl-) urea, uric acid, ammonia, amino acids, glucose, lactic acid 6. Fxn: regulate body temp (thermoregulation) – evaporation cools body; waste removal a. Includes emotional sweating – nervous, getting ready for a test ii. Apocrine sweat glands 1. Simple coiled tubular; larger ducts than eccrine 2. In axilla, groin, areolae (pigmented area across the nipples), bearded regions 3. Used to think they all pinched off in apocrine manner; but only mammary glands do this; the rest are really eccrine in nature (exocytosis of sweat vesicles) 4. Secretions are similar to eccrine, but also contain lipids and proteins 5. Body odor – bacteria begin to feed on proteins secreted 6. Begin functioning at puberty 7. Stimulated during stress and sex, not for thermoregulation VII. 3. Ceruminous Glands a. Modified sweat glands of external ear b. Produce waxy lubricating solution c. From Sub-Q layer, deep to sebaceous glands d. Opens to surface pores or to ducts of sebaceous glands e. Cerumen = ear wax f. Fxn: i. Prevents entrance of foreign bodies (insects), bacteria, fungi & viruses ii. Waterproofs ear canal g. Tx if overproduced: ear irrigation with enzymes or warm liquid. iii. Nails 1. Plates of dead hard packed keratinized epidermal cells 2. Nail body (plate) – visible portion of nail (like stratum corneum of skin) a. Free edge: part of nail body extending past distal end of digit (good for scratching), white due to no capillaries b. Nail root: buried in a fold of the skin c. Lunula: whitish crescent-shaped area at base (thickened stratus basale doesn’t allow vessels to show through) d. Hyponychium: b/n free edge and skin of fingertip – secrures nail to fingertip e. Nail bed: skin below nail plate (lunula to hyponychium) f. Eponychium (cuticle): narrow band of epidermis adhering to nail wall g. Nail matrix: epithelium proximal to nail root, area of mitotic cell division for nail growth. Aging of Skin a. Effects seen at 40 yrs of age i. ↓ # fibroblasts → ↓ collagen: ↓ in #, becomes disorganized, stiffens and breaks; elastic fibers: ↓ elasticity, becoming thicker and fray ii. ↓ Sub-Q adipose → thinning & decreased protection resulting in more skin tears iii. Growth of hair & nails slows as early as 2nd & 3rd decade (teens & 20’s) iv. ↓ intraepidermal macrophages → ↓ immune response v. ↓ size of sebaceous glands → dry, cracked skin → ↑ bacterial infections vi. ↓ fxn of sweat glands → ↓ sweating → heat stroke vii. ↓ fxn of melanocytes → grey hair b. Anti-aging Treatments i. Topical products -bleaching` ii. Microdermabrasion - crystals to vacuum/scrub skin surface iii. Chemical peel – using mild acids to remove surface layers iv. Laser resurfacing – clears blood vessels near the surface v. Dermal fillers – injection of collagen, hyaluronic acid to plump up skin/smooth wrinkles vi. Fat transplantation – fill in around the eyes vii. Botox – injection of diluted botulinum toxin to paralyze muscles viii. Facelift – using radio frequency or invasive surgery to tighten/remove sagging skin

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