EXSC%223:%Week%of%9/26/16%!Textbook%notes%5.1-5.4,%5.8%5.1!The!skin!consists!of!two!layers:!the!epidermis!and!dermis!• Skin!weighs!9-11!pounds!• Varies!in!thickness!depending!on!the!area!of!the!body!• Composed!of!2!distinct!layers!o Epidermis!§ Made!of!epithelial!cells!§ Outermost!protective!shield!of!the!body!o Dermis!§ Makes!up!the!bulk!of!the!skin!§ Made!of!dense!connective!tissue!§ Vascularized!• Nutrients!reach!the!epidermis!by!diffusing!through!the!tissue!fluid!from!blood!vessels!in!the!dermis!o Hypodermis!§ Subcutaneous!tissue!just!below!the!dermis!§ Technically!NOT!part!of!the!skin!§ Also!called!superficial!fascia!§ Consists!mostly!of!adipose!tissue!§ Functions:!!• stores!fat!• anchors!the!skin!to!underlying!structures!• shock!absorber!• insulate !!5.2!The!epidermis!is!a!keratinized!stratified!squamous!epithelium !• epidermis!has!!o 4!cell!types!o 4!or!5!distinct!layers!§ all!epidermises!have!at!least!4!layers!§ thick!skin!(soles!of!feet!an d !palm s!o f!han ds)!h ave !a!5th!layer!• thickest!skin!in!the!bo dy!is!on !the !upp er!b ack!• cell!types!o keratinocytes!§ function:!pro du ce !keratin!• fibrous!protein !tha t!gives !epid erm is !pro tective !pro pe rties!§ most!epidermal!cells!are!keratinocytes!§ connected!by!desmosomes!§ they!start!in!the!dee pe st!laye r!of!the !epid erm is!(stratu m !ba sale)!an d!are!pushed!upward!by!the!production!of!new!cells!to!the!stratum!corneum !• dead!by!the!time!they!reach!the!stratum!corneum!§ rub!off!by!abra sion !• new!epidermis!every!25-45!days!§ callus:!thickening!of!the!epidermis!o melanocytes!§ spider!shaped!§ function:!syn the size !m elan in!(p igm e nt) !§ found!in!the !dee pe st!la y er !of !th e !ep id e rmis!§ melanin!packaged!into!melanosomes!where!they!are!transferred!to!keratinocytes!• function:!prote cts!n uc lei!from !U V !radia tion!o Langerhans!cells!§ Dendritic!cells!§ Ingest!fo r eig n !s u b st a n ce s!§ Key!activators!of!immune!system!§ Slender!processes!extend!among!surroun ding !kera tinoc ytes!fo rm ing!a !continuous!network!o Merkel!cells!§ Tactile!cells!§ Present!at!epidermal-dermal!junction!§ Shaped!like!a!spiky!hemisphere!§ Sensory!receptors!• Layers!o Stratum!basale!(basal!layer)!§ Deepest!epidermal!layer!§ Attached!to!the!underlying!dermis!along!a!wavy!border!§ Single!row!of!stem!cells!that!produce!more!keratinocytes-constantly!undergoing!mitosis!• When!one!of!the!basal!cells!divide,!a!daughter!cell!is!pushed!into!the!cell!layer!above!to!begin!specialization!into!a!mature!keratinocyte!• The!other!daughter!cell!stays!in!the!stratum!basale!to!produce!more!keratinocytes!§ 10-25%!of!cells!in!this!layer!are!melanocytes!o stratum!spinosum!(prickly!layer)!§ several!cell!layers!thick!§ contain!weblike!system!of!intermediate!filaments!• mostly!tension-resisting!bundles !of!pre -keratin!filaments!§ keratinocytes!appear!to!have!spines!§ there!are!also!m elan in!gra nu les!an d!La ng erh an s!cells!in!this!layer!o stratum!granulosum!(granu lar!layer)!§ 1-5!cell!layers!§ keratinization!begins!(cells!fill!with!keratin)!• cells!flatten!• nuclei!and!organelles!begin!to!disintegrate!• accumulate!2!types!of!granules!o keratohyaline:!help!form!keratin!in!upper!layers!o lamellar:!c o n ta in !w a te r-resistant!glycolipid!tha t!is!spew e d!into !extracellular!space!§ function:!slow !w ate r!loss !in!the!e p id er m is !• too!far!from!nu trients !and !glyco lipids!from !lam e llar!gran ules !cuts!th em !off!from!nutrients!so!they!start!to!die!o stratum!lucidum!(clear!layer)!§ only!in!thick!skin!§ 2!or!3!rows!of!clear,!flat,!dead!keratinocytes!o stratum!corneum!(horn y!layer)!§ outermost!epidermal!layer!§ anucleated!cells!§ dead!keratinocytes!§ 20-30!cell!layers!thick!§ protect!skin!from!abrasion!§ on!average!people!shed!50,000!dead!cells!every!minute!!5.3!The!dermis!consists!of!papillary!and!reticular!layers!• Dermis!is!made!up!of!connective!tissue!o Typical!cells!of!connective!tissue!proper!§ Fibroblasts!§ Macrophages!§ Mast!cells!§ White!blood!cells!• Has!a!rich!supply!of!nerve!fibers,!blood!vessels,!lymphatic!vessels!• Two!layers:!papillary!and!reticular!• Papillary!layer!o Areolar!connective!tissue!o Collagen!and!elastic!fibers!are!woven!together!and!connected!with!blood!vessels!o Loose!connective!tissue!allows!for!phagocytes!and!other!defensive!cells!to!wander!through!o Dermal!papillae:!peg-like!proje c tio n s!fr o m !it s!s u rfa ce !in d en t !th e!e p id e rmis!• Reticular!layer!o 80%!of!the!thickness!of!the!dermis!o coarse,!dense!irregular!connective!tissue!o extracellular!matrix:!adipose!cells!and!collagen!fibers!§ direction!the!collagen!runs!forms!cleavage!(tension)!lines!§ incisions !made!para lle l!to !th e s e!lin e s!h e a l!fa ste r!a n d !b et te r!o collagen!gives!skin!strength!and!resilience!o collagen!also!!binds!water!which!helps!keep!skin!hydrated!!5.4!Melanin,!carotene,!and!hemoglobin!determine!skin!color!• melanin!o polymer!made!of!tyrosine!amino!acids!!o has!two!forms!that!range!in!color!from!reddish!yellow!to!brownish!black!o synthesis!is!in!melanocytes!o found!only!in !the!d ee pe st!laye rs!of!the !ep ide rm is !o prolonged!sun!exposure!causes!a!build!up!of!melanin!to!protect!from!UV!exposure!• carotene!o yellow!to!orange!pigment!found!in!plant!products!§ ex:!carrots!o accumulates!in!the!stratum!corneum!and!in!fatty!tissue!of!hypodermis!o in!the!bo d y,!it !ca n !b e!c o n ve rte d !in to !v ita m in !A !• hemoglobin!o causes!the!pinkish!hue!of!fair!skin!o oxygenated!pigment!has!a!crimson!color!o in!the!red !b lo o d !ce lls!c ircu la tin g !in !th e !d er m a l!c ap illa rie s !• alterations!in!skin!color!!o redness!or!eryth em a :!redd en ed !skin!b eca us e!of!blu sh ing,!feve r,!hyp erte nsio n,!inflammation,!aller gy !o pallor!or!blanching:!pale!because!of!fear,!anger,!emotional!stress,!anemia,!low!blood!pressure!o jaundice !o r!y ello w!cast:!yellow!skin!ton e!because!of!liver!disorder!o bronzing:!bronze!metallic!appearance!of!the!skin!because!of!Addison’s!disease!o bruises:!blood!clot!beneath!the!sking!• skin!appendages!o hair/hair!follicles!o nails!o sweat!glands!o sebaceous!(oil)!glands!!5.8!First!and!foremost,!the!skin!is!a!barrier!• functions!of!the !skin :!p r o te ct io n ,!b o d y !te mperatu re !re gulation,!cu ta n e o
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