Integumentary System PDF

Anatomy & Physiology I BIOL 2001 C Ibanez Integumentary System pp. 152-179 1. Integumentary System: an organ system that covers the exterior of the body a. Cuta...

Anatomy & Physiology I BIOL 2001 C Ibanez Integumentary System pp. 152-179 1. Integumentary System: an organ system that covers the exterior of the body a. Cutaneous membrane (skin) composed of epidermis & dermis i. Subcutaneous or hypodermis is deep to this membrane b. Accessory structures: i. Hair, hair follicles & sebaceous glands ii. Sweat glands iii. Nails iv. Sensory receptors 2. Major system of blood vessels throughout the membrane (not beyond basement membrane of epidermis though) 3. Functions of the Integument: a. Protection: mechanical, biological, fluid loss b. Excretion: NaCl, H20, and organic wastes c. Maintenance of body temperature d. Production: melanin (UV protection), keratin (water resistance), Vitamin D (helps with Ca++ absorption) e. Storage: fat in dermis (and subcutaneously too) f. Sensation: touch, temp, pain, vibration 4. Epidermis: stratified squamous epithelial cells a. Avascular b. Cells divide at basal lamina c. Cells of the epidermis are called keratinocytes 5. Layers of Epidermis (from basement membrane upward) a. Thin skin = 4 layers b. Thick skin = 5 layers Anatomy & Physiology I BIOL 2001 C Ibanez c. Stratum Germinativum i. Forms ridges (matches underlying dermal papillae): why? increased surface area = increased grip ii. Basal cells (stem cells): these cells divide and push up into next cell layer iii. Merkel cells extend into this region in hairless skin for sensitive touch iv. Melanocytes also present for melanin production d. Stratum Spinosum i. Start becoming dehydrated = spiny looking ii. Contain dendritic cells (immune function) iii. Some cells divide and push up into next cell layer iv. 8 to 10 cells thick e. Stratum Granulosum i. No more cell division, but still being pushed up by cell division from below ii. Produce: 1. Keratin: protein fiber 2. Keratohyalin: dehydrates cell, glues keratin fibers together iii. 3 to 5 cells thick f. Stratum Lucidum (found in thick skin only such as palms and soles) i. Flat, thin, no organelles: just keratin = glassy looking (lucid) g. Stratum Corneum i. All exposed skin except anterior surface of eyes ii. All dead & totally keratinized iii. Tightly linked by desmosomes iv. 15 to 30 cell layers thick v. Water resistant, not waterproof: 1. Insensible water loss due to airs hypertonicity = 500 mL/day 2. Sensible water loss (made by sweat glands) varies depending on the individual, environment, activity 6. Melanocytes a. Carotene accumulates in stratum corneum in persons with low melanin b. Found in stratum germinativum and extends up into stratum spinosum (in lighter skinned individuals) and into stratum granulosum (in darker skinned individuals) Anatomy & Physiology I BIOL 2001 C Ibanez c. Make melanin: pigment that is brown, black, or yellow-brown i. Pigment is packaged in melanosomes (can be small or big) and sent to keratinocytes (ratio of 1:4 to 1:20 melanocytes: keratinocytes depending on place on body) d. Skin color differences due to: i. Genes (378 genes that we know of) ii. Small vs. big melanosomes iii. Layer the melanosomes are deposited into (spinosum vs. granulosum) iv. Numbers of melanosomes made e. Freckles: irregular border, melanocytes are extra productive compared to others in skin f. Lentigos: regular border, defective melanocytes due to sun exposure g. Function: protects nucleus from UV radiation (causes mutation in DNA) 7. Vitamin D a. In skin, UV rays convert cholesterol → cholecalciferol (D3) → goes to liver → converted to an intermediary → to kidney and used to synthesize calcitrol → increased absorption of Ca++ & PO4-3 from the digestive tract 8. Dermis – between epidermis & subcutaneous layer a. Papillary layer: areolar connective tissue, capillary network (papillary plexus), neurons b. Reticular layer: dense irregular CT, neurons, capillary network (cutaneous plexus), contains epidermal extensions (hair follicles, sweat glands, sebaceous follicles & glands, and nails) c. Collagen and elastin fibers are found throughout the dermis = flexible and strong affected by aging, hormones, hydration status, etc. Anatomy & Physiology I BIOL 2001 C Ibanez d. Contusion (bruise): rupture of small dermal blood vessels: turns black-n-blue → green → yellow (immune response) 9. Hypodermis (subcutaneous): not part of integument a. Stabilizes position of skin b. Areolar & adipose tissues - very elastic c. Superficial layer = blood reservoir & heat exchange d. Deeper layer = low capillaries (good place for injections meant to be absorbed slowly) 10. Accessory structures: physically located in the dermis but epidermal in origin (that’s why they grow all the time) a. Hair: i. Structure: hair follicle produces hair ii. Extends from surface of the epidermis deep into the dermis or hypodermis iii. Made up of root plexus (nerves & blood vessels) at the base iv. Arrector pili (muscle attached to papillary layer of dermis & connective tissue sheath around hair follicle v. Hair root 1. Bulb around papilla (Connective tissue with blood & nerves) 2. The bulb cells form a matrix: these cells divide and are keratinized a. Center = medulla, contains soft keratin b. Middle = cortex; Edge = cuticle: both contain hard keratin vi. Hair shaft vii. Types: 1. Lanugo: embryonic 2. Vellus: peach fuzz 3. Terminal: heavy with pigment, thick, can be curly viii. Color due to melanocytes in papilla; changes due to hormones, chemo, age 1. Dyes go into cortex and even medulla by disrupting the cuticle = weaker hair Anatomy & Physiology I BIOL 2001 C Ibanez b. Sebaceous Glands i. Holocrine production of oil (sebum): inhibits growth of bacteria; protects the hair shaft; conditions skin; associated with hair shaft c. Sebaceous Follicles are not associated with hair shaft; directly dump sebum on skin d. Sweat Glands i. Merocrine ii. Armpits, groin, nipples: secrete onto hair follicles iii. Become active at puberty; stimulated by nervous and endocrine system e. Mammary glands i. Apocrine f. Nails i. Root near bone: epithelial in origin; where cell division and keratinization take place ii. Cuticle (eponychium; epi = upon; onych = nail): stratum corneum from the root that extends over exposed nail iii. Nail body (visible portion) over top of nail bed iv. Free edge extends over hyponychium: thickened stratum corneum v. Lunula: area of low blood vessels, so it appears white 11. Repair of injury a. Stratum germinativum in epidermis i. cells begin dividing and move in along edges of injury; macrophages eating debris & pathogens b. Mesenchymal cells and fibroblasts in connective tissue c. Blood clot: restores physical integrity; mostly fibrin fibers Anatomy & Physiology I BIOL 2001 C Ibanez d. Dermis is fixed first: mesenchymal cells divide/differentiate, and fibroblasts lay down a lot of collagen & ground substance e. Capillary growth follows the fibroblasts (granulation tissue) f. Epidermal cells migrate over meshwork produced by fibroblasts g. Clot dissolves, capillaries retreat, scar tissue laid down 12. Burns: a. 1st and 2nd = partial thickness b. 3rd = full thickness c. 1st is epidermal damage only: red skin, painful d. 2nd is epidermal and some dermal damage: blisters form between epidermis and dermis, red skin, painful, may scar e. 3rd is destruction of both epidermis and dermis; it may involve tendons and bones as well; relatively painless due to destruction of sensory nerves, cannot repair itself-may require a skin graft. f. Skin function is compromised leading to fluid/electrolyte imbalances, issues with thermoregulation, and increase susceptibility to infection. 13. Changes associated with aging: a. Germinative cell activity declines & connections weaken; prone to injury & infection b. Reduced number of immune cells c. Vitamin D production decreases by 75% d. Melanocyte activity decreases: more prone to sunburn e. Glandular activity decreases: less sebum = dry, scaly; less sweat = hyperthermia f. Blood flow decreased: makes you feel cold, but you aren't g. Dermis thins and elastic network decreases in size h. Repairs proceed more slowly (less blood supply, reduced immune function)