9-l The Skin Th.: skin is the pri mary organ of the intexumemary system and i~ the largest organ of the body. Forming the outer protecti ve covering of the hody. the skin is a rontinuous sheet of cutaneous rncmhrunc. Before You Begin D Read the appropriate chapter in your textbook. tJ Set your learning goals. Whe n you fini sh this exerci se. you should be able to: • describe the major structures of the skin and identify their functions • identify important skin structures in a diagram, model, and prepared spcdml'n • romparc and l'Olltr.i,t lt:ature~ of th il·k ~kin and thin 0 \kin D Prepare your matenab: • model or chan of a skin cros~ ~el· tion • microscope • prepared microslides: thin skin section thick skin .1ectio11 l111ir fol/ ic/1'1 1·. 1·. D Carefully reaJ the directions anJ safely tips for this exercise before ~taning any procedure. A. Basic Skin Structure First in a model, then in prepared microscopic spc:dmcns. identify the elements of skin structure iJcntified in the following steps. · .1 ·: · SAFETY·FIRST! ... . □ 2 . Don't forget the rules for safe uu of the microscope. □ 1 The -skin has two distinr.:t layers. The superficial layer is a sheet of keratinizcd stratified squamous epithelium called the epidermis. The epidermis is it~elf Jiviued into distinct histological regions, or strata (rneaning "layers''): • Stratum basale is the deepest stratum of the epiuermis. It consists of a single sheet of columnar cells that continue to divide. As the daughter ~ells are formed, they are pushed upward, becoming part of the next stratum. • Stratum spinosum is noted for its multilayer of distoneu ("spined") cells. The cells become distoned as they are pushed up from the deeper stratum basale and look somewhat "spiny" when stained and prepared for microscopy. Stratum basale and stratum spinosum together are often l·allcJ stmt11m xer111i11ativ11m. • Stratum granulosum is superficial to strntum spi1Hhlllll. It l 0l1tai11s tl,ltll'IH.:d ,·t:11_, pw,hed 11r from thr dl'q'k.·r ~trata. ,\, thl· n ·II, :in: pw,h,•d up 1lm111µh th1, ,trat11111, thl')' ll1r111 lhl' p1111cin _.: ranulc, that give 11 the name grww/0 111111. By the time.: the l'ells lca\'e 1hi~ stratum. they have died. • Stratum lut'idum tnll·aning "'light b)1..•r"'1 is a very 1h111 !.1yi:r prl'Sl'llt only in thick skin. Thil·k ,kin is founu only in high-wear areas such as the palms and soles. The more fle xible thin skin i~ found over mlist other areas of the bo<ly. This stratum's name rnmes from the far.:t that it is translucent, allowing light to pass through it easily. • Stratum corncum b the layer of deaJ, keratinized tis~uc alreaJy identif\l'd in Lah EKl'rrise 5. Stratum rnrucum is extrt·mely thick in thi1,:k !skin. providing a gre<1t ,kal of prntel·fi,m. Stratu111 c.:ornt·um pnitel·ts tkl.'per tissues fro111 med1anil'al injury, inward or outwarJ Jiffusion \lf wutcr um! other 111okr.:ules, and inva~ion by minuorganism~. The layer of skin deep to the cpidcnni~ is a sheet of irregular fibrous connective tissue calleJ the dermis. The dermi~ is usually much thicker than the epidermis. Like most conne1:tivc tissues, the Jem1is has a scattering of blood vessels and nerves. The blood vessds supply both the dcm1is and epidcnnis. Bcr.:ause blood cools when it travels through the skin, 1hc body varies the amount of blood sent to the skin · to n.:gulate loss of heut by the entire body. The dcnnis contains many sensory nerve endings. Se nsations such as heat, cold. touch. and pressure are mediated 57 ■ o hy dermal nerve endings. The~ arc two regions of the dermis: • The rttlculur luyer of 1he dermis is u thick region of irregularl y urrangctl protein fibers. Most of the fibcri, arc collage nous, but a few are made of d a~tin. • The papillary layer is the bumpy supe~cial . portion of the dermis attached to the ep1dcnrns. The bumps. called papillae (meaning ."nipples"), form regular rows in thick skin but ate rather irregularly arranged in thin skin. For this reason, thick skin can be observed to have distinct ridges. such as fingerprints. These ridges give the hands and feet better gripping ability. 3 Deep to the skin is a layer of subcutaneous tissue, · sometimes called the hypodermls or supertlclal fascia. Although not a part of the skin, it is often studied along with skin. Subcutaneous tissue is loose, fibrous (areolar) connective tissue that connects the ~kin to underlying muscles and bone. Some of the areolar tissue has been modified to become adipose tissue. Adipose tissue's protective and insulating characteristics complement the protection and temperature regulation roles of the skin. Hint. . . Minircfercnce Plate 7 shows light micrographs of 1kin suucturc,. Plate 7a represents thin skin, Plate 7b thick skin, Plate 7c thin skin with hair follicles and other accessory structures, and Plate 1d thin skin with sweat glands. B. Hair, Nails, and Glands The skin has a variety of accessory structures, including hair and nails. Both hair and nails are modified forms of stratum corneum, or keratini~ed tissue. Hair is a cylinder of compact keratinized material, and a nail is a plate of compact keratinizcd material. Identify the structures described here in a model and in prepared specimens. D 1 Each hair is formed within a separate hair follicle. The follicle is a sheathlike indentation of the epidermis. At the bottom of the follicle, a hair ' . h tratum genninativum produces 11 papilla covered ~ sf each hair within the follicle is . Th poruon o . h the hair. e hcreas the part1on thut as • hulr root, w · h l rn II cd thc of the follicle is called the a r been pushed ~ut dense cortex and a less shaft. The hair has a very dense medulla. h ~ tr cle is an exocrine (ducted) , Attached to cac o i_ land produces the fatty sebaceous glaDd , This g h hair and skin substance sebum, that coats l e .. th. h . ' .sture loss and conditions e au Sebum prevents mm. . d ·1 . . h· t ·1 docsn 't become bnttle an eas1 y 1 and skm sot u • broken. th 1 0 3 The arrector pili muscle is a stra~ of smoo muse e tissue connecting the side of a follicle to the superficial surface of the dennis (fig. 9.1 ). Wh~n. contracted, the muscle pulls the follicle so th~t.it is nearly perpendicular to the skin's su~ace: This . increases the air spaces among the hairs, 1mprovm_g_ its insulation quality. Contra~tion of the arrector p1h also dimples the epidermis, raising a ridge at the edge of the follicle (a "goosepimple"). n 4 The toenail or fingernail is also formed by a modified portion of stratum germinativum. In the case of either hair or nail, this modified tissue is often called matrix. A portion of the nail bed (skin under the · nail) is matrix that produces the nail plate. Part of tht matrill may be visible through the nail as a pale crescent, or lunula. Nail formation begins under a fold of epidermis. The portion of the nail under the fold is the root, and the visible portion is the nail body. A cuticle, or eponychium, may extend from the fold onto the nail body (fig. 9.2). D S Sweat glands are _found in many areas of the skin. They are exocrine glands that produce a watery solution, sweat, that coats the skin. Sweat serves primarily to improve heat loss by the sk.in through evaporation. Eccrine sweat glands produce thin, watery sweat in many areas of the body. Apocrine ~weat glan~s. found in the axillary and pubic regions, . secrete a thicker sweat that is rich in complex organic molecules. Review what you have learned about skin by comp) t' g figure 9.3. em □ 2 by dermal nerve endings. There are two regions of the dermis: • Thl· reticular luyer of the dermis is a thick region of irregularly arranged protein fibers. Most of the fibers arc collagenous, but a few are made of elai.tin. ' • The papillary layer is the bumpy superficial portion of the dennis attached to the epidermis. The bumps, called papillae (meaning "nipples"), form regular rows in thick skin but are rather irregularly arranged in thin skin. For this reason. thick skin can be observed to have distinct ridges, such as fingerprints. These ridges give the hands and feet better gripping ability. D 3 Deep to the skin is a layer of subcutaneous tissue, . sometimes called the hypodcrmls or superfklal fascia. Although not a part of the skin, it is often studied along with skin. Subcutaneous tissue is loose. fibrous (areolar) connective tissue that connects the skin to underlying muscles and bone. Some of the areolar tissue has been modified to become adipose tissue. Adipose tissue's protective and insulating characteristics complement the protection and temperature regulation roles of the skin. ·11 covered with stratum germinativum produces papi 8 · · h' h f 11· I . the hair. The portion of each hair wit _m t e o ic e is rnlkd the hulr root, whereas the portion that has been pushed out of the follide is called the hair shaft. The hair has a very dense cortex and a less dense medulla. Attached to each follicle is an exocrine (ducted) , sebaceous gland. This gland produces the fatty substance, sebum, that coats the hair and skin. Sebum prevents moisture loss and conditions the hair and skin so that it doesn't become brittle and easily broken. □ 3 The arrector pili muscle is a strap of smooth muscle tissue connecting the side of a follicle to the superficial surface of the dermis (fig. 9.1 ). When contracted, the muscle pulls the follicle so that it is nearly perpendicular to the skin's surface. This increases the air spaces among the hairs, improving its insulation quality. Contra~tion of the arrector pili also dimples the epidermis, raising a ridge at the edge of the follicle (a "goosepimple"). n 4 The toenail or fingernail is also formed by a modified portion of stratum genninativum. In the case of either hair or nail, this modified tissue is often called matrix. A portion of the nail bed (skin under the nail) is matrix that produces the nail plate. Part of the Minircfcrcncc Piute 7 shows light micrographs matrix may be visible through the nail as a pale of skin structures. Plate 7a represents thin skin, Plate 7b thick crescent, or lunula. Nail formation begins under a skin, Phatc 7c thin skin with hair follicles and other accessory fold of epidermis. The portion of the nail under the structures, and Plate 7d thin skin with sweat glands. fold is the root, and the visible portion is the nail body. A cuticle, or eponychium, may extend from the fold onto the nail body (fig. 9.2). D 5 Sweat glands are _found in many areas of the skin. They arc exocrine glands that produce a watery solution, sweat. that coats the skin. Sweat serves The skin has a variety of accessory structures, including hair and nails. Bo~h hair and nails are modified forms of stratum primaril~ to improve heat loss by the skin through corneum, or keratinized tissue. Hair is a cylinder of compact . evaporation. Eccrine sweat glands produce thin, keratinized material, and a nail is a plate of compact watery sweat in many areas of the body. Apocrine keratinized material. Identify the structures described here in sweat glan~s. found in the axillary and pubic regions, a model and in prepared specimens. . secrete a thicker sweat that is rich in complex organic molecules. 0 1 Each hair is formed within a separate hair follicle. Review what you have learned about skin by completing figure 9.3. The follicle is a shcathlike indentation of the epidennis. At the bottom of the follicle, a hair Hint. .. B. Hair, Nails, and Glands □ 2 Contracted ~igure 9.1 When the arrector pili contracts, it pulls the follicle and hair into a perpendicular position, improving the nsulation quality of the hair. Notice how a "gooscpimple" is raised around the follicle opening. 2 3 4 5 Figure 9.2 Label this ~ec.:tion of a finger with the appropriate terms. 59 9-4 The Skin EPIDERMIS ~~·u·Llt1/,a~U'liJJlMJ ©CQ)fRlWJ~lUJlMl 1 ~iJ'lR1ffeiiJ'll1l~ [1,lVJ©O@!lfl~ 2 ~· lflxli~u'QJJ!Ml @~[N](lJ)[L©~lVJ~ ~tf~"fflVJ~ ~IP-lO!Nl@~lVJ~ 4 @tf'MiJ'lVJIM! ~~~ffi\[L[g s 3 5 DERMIS [j2)ffi\lP-l0ll~!R1W ~ W[g!Rl 6 !Rl~O©M~!R1 ~W~ 1 ®~~If @~INJIQ) 8 @[1,(Q)(Q)IQ) '¥1~~~[1, 9 !NJ (g[R1'¥7[g 10 HAIR [ru(Q)(Q)lJ' 11 ©IXIC\\lN 12 ~(Q)[1,[L0©[1,~ 13 ~ffi\~ 0[1,~ 14 ~;,%if~□~ 16 ffi\(R1~~©1f©[R1 ~0[1,0 10 16 ®(g@ffi\(g[g(Q)lVJ~ @~INJ[Q) · IXIW[f2)(Q)[Q)~!Ri~U® . . . . . . Figure 9.3 60 17 10 Use colored pens o r pen.:ils to col or in labels and struc ture~ of (a) thin skin and (b) thicl< skin. ' The Skin Specimen: thin skin section Total magnification: _ _ Specimen: thick .rkin .rection Total magnification: _ _ N:Jllll ' - - - - - --- - - - - -- - - - - -- - Dale _ _ _ _ __ _ __ Specimen: hair follicles c.s. Specimen: - -- -'--- - Sl·cri11n Total magnification: _ _ Total magnification: _ 61 Fill-in Figure 9.2 1. 2. 3. 4. _ _ _ _ __ __ _ 2 ---------- 3 _ __ _ __ _ _ 4 The _]_ is the superficial layer (of two) in the c;ki n. The hypmlcrmi~ ii- 111ni11ly an:ola, und _ 1_ 11"11c fingerprint ridges arc formed a~ a result of the orderly arrangement of derma l _1_. Stratum comeum is composed of dead cell parts and a tough. waterproof protein called ., __.___. _________ 5 Fill-in __________ 2 '.'i. Strut um _j__ b the cpidcnnal ~tralum in wl11d1 one could find muny phu.-.c~ of mitll-ik 6. Cells are pushed into stratum _.1_ from stratum basale. 7. When you sense cold air around you, nerve endings in the _1_ are probably involved. 8. When you sense cold air around you, bumps may appear on the skin. This is caused by the contraction of the _.1_. 9. The subcutaneous tissue is also called the superficial fascia, or_]_. 10. Physiologists believe that some sweat glands produce aromatic. organic molecules called pheromones that may serve sex attractants. The type of sweat gland (of the two discussed in this exercise) most likely to produce pheromones is __'J__. 11. Strong shampoo tends to remove _1_ from the hair and scalp, making it dry and eas ily damaged. 12. The eponychium, or_]_, covers part of the oail plate. 13. When you have your hair cut, the portion of the hair trimmed is called the _1_. 14. Blood vessels that supply the ep.idermis are found in the_?_ region of the dermis. 15. Stratum basale and stratum spinosum together may be called stratum_]_. 16. Keratinized --1._ epithelium forms the epidermis. · 17. The dermis is composed mainly of_?_ fibers. with a few elastic fibers. 18. Stratum --1._ is usually absent in thin skin. 19. _1__ glands produce sebum. 20. The most widely distributed type of sweat gland is the _]_ type of gland. as _________ 3 __________ 4 • ---------- 5 _________ 6 __________ 7 _________ 8 __________ 9 10 _ _ _ _ _ _ _ _ _...... 11 - - - - - - - - - 12 __________ 13 Table Fill in the spaces that are blank. - - - - - - - - - 14 15 - - - - - - - - - 16 - - - - - - - - - 17 - Characterbtlc Epldennls Tissue type Presence of blood vessels - -- - - - - - 18 - - - - - - - - - 19 - - - - - - - - - 20 Relative thickness Permeability Relative strength Short answer Write a few complete sentences. How docs thin skin di ffer from thick ~kin? 62 l Dennla ..
