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1
C H A P T E R
5
The Integumentary
System
The Skin and the Hypodermis
• Skin – our largest organ• Accounts for 7% of body weight• Divided into two distinct layers
• EpidermisD i
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• Dermis• Hypodermis – lies deep to the dermis
Figure 5.2 Gross structure of skin and underlying tissues.
Epidermis
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p
DermisHypodermisDeep fasciaMuscle
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The Skin and the Hypodermis
• Functions• Cushions and insulates deeper organs• Protects body from bumps, scrapes, and cuts• Protects body from chemicals, heat, and cold
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• Acts as a mini-excretory system• Screens out UV rays from the sun• Contains sensory receptors associated with nerve
endings
Skin Structure
Epidermis
Hair shaft
Papillarylayer
Dermal papillae
Pore
Subpapillary vascularplexus
Figure 5.1
DermisReticularlayer
Hypodermis(superficial fascia)
Appendages of skinEccrine sweat glandArrector pili muscleSebaceous (oil) glandHair follicleHair root
Nervous structuresSensory nerve fiberLamellar (Pacinian)corpuscleHair follicle receptor(root hair plexus)
Dermal vascular plexus
Adipose tissue
• Provides mechanical protection• Prevents fluid loss• Keeps microorganisms from invading the body
The epidermis
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Epidermis
• Contains four main cell types• Keratinocytes• Melanocytes• Merkel cells (tactile)• Langerhans (dendritic) cells
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Epidermis
• Keratinocytes – most abundant cell type in epidermis• Arise from deepest layer of epidermis• Produce keratin – a tough fibrous protein
P d tib di d
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• Produce antibodies and enzymes• Keratinocytes are dead at skin's surface
• The epidermis is composed of layers of keratinocytes• Thin skin = four layers (strata)• Thick skin = five layers
Thin Skin and Thick Skin
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Layers of the Epidermis
• Stratum basale (stratum geminativum) • Stratum spinosum• Stratum granulosum• Stratum lucidum (only in thick skin)
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• Stratum corneum
Epidermal Cells and Layers of the Epidermis
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Layers of the Epidermis
• Stratum basale• Deepest layer of epidermis• Attached to underlying dermis• Cells actively divide
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• Stratum basale contains• Merkel cells – associated with sensory nerve ending• Melanocytes – secrete the pigment melanin
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Layers of the Epidermis
• Stratum spinosum (spiny layer)• "Spiny" appearance caused by artifacts of
histological preparation• Contains thick bundles of intermediate filaments
(tonofilaments)
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(tonofilaments)• Contains star-shaped Langerhans cells
Layers of the Epidermis
• Stratum granulosum• Consists of keratinocytes and tonofilaments • Tonofilaments contain
• Keratohyaline granules – help form keratin• Lamellated granules – contain a waterproofing glycolipid
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Layers of the Epidermis
• Stratum lucidum (clear layer)• Occurs only in thick skin• Composed of a few rows of flat, dead keratinocytes
• Stratum corneum (horny layer)
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• Thick layer of dead keratinocytes and thickened plasma membranes
• Protects skin against abrasion and penetration
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• Cells accumulate keratin and eventually are shed• Epidermal ridges are interlocked with dermal papillae
• Fingerprints • Improve gripping ability
• Langerhans cells (immunity) in stratum spinosum
Epidermal characteristics:
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• Merkel cells (sensitivity) in s. germinativum
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Friction ridgesOpenings of sweat gland ducts
Dermal Modifications
(a) Friction ridges of finger tip (SEM 20×)
(b) Cleavage lines in thereticular dermis
(c) Flexure lines of the hand
Flexioncreaseson digitFlexion creaseson the palm
Figure 5.6
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Dermis• Second major layer of the
skin• Strong, flexible connective
tissue• Richly supplied with blood
vessels and nerves
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• Has two layers• Papillary layer – includes
dermal papillae• Reticular layer – deeper
layer – 80% of thickness of dermis
Hypodermis• Deep to the skin – also called superficial fascia• Contains areolar and adipose connective tissues • Anchors skin to underlying structures• Helps insulate the body
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Skin Color
• Three pigments contribute to skin color• Melanin – most important pigment – made from
tyrosine• Carotene – yellowish pigment from carrots and
tomatoes
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tomatoes • Hemoglobin – Caucasian skin contains little melanin
• Allows crimson color of blood to show through
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Appendages of the Skin
• Hair• Flexible strand of dead, keratinized cells• Hard keratin – tough and durable• Chief parts of a hair
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• Root – imbedded in the skin• Shaft – projects above skin's surface
Appendages of the Skin
• Hair – three concentric layers keratinized cells• Medulla – central core • Cortex – surrounds medulla• Cuticle – outermost layer
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Cross Section of a Hair
Hair shaft
Arrector
Connective tissueroot sheath
Follicle wall
Cuticle
Glassy membrane
CortexMedulla
Internal epithelial root sheath
External epithelialroot sheath
Hair
Figure 5.8a, b
ArrectorpiliSebaceousgland
Hair root
Hair bulb
(a) Diagram of a cross section of a hair within its follicle
Hair shaft
ArrectorpiliSebaceousgland
Hair root
Hair bulb(b) Photomicrograph of a cross section
of a hair and hair follicle (185×)
Connective tissueroot sheath
Follicle wall
Cuticle
Glassy membrane
CortexMedulla
Internal epithelial root sheath
External epithelialroot sheath
Hair
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Appendages of the Skin
• Hair follicles – extend from epidermis into dermis• Hair bulb – deep, expanded end of the hair follicle• Root plexus – knot of sensory nerves around hair
bulb• Wall of hair follicle
• Connective tissue root sheath
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• Epithelial root sheath• Arrector pili muscle – bundle of smooth muscle
• Hair stands erect when arrector pili contracts
Hair shaft
ArrectorpiliSebaceousgland
Hair root
Hair bulb
Internal epithelialroot sheath
External epithelialroot sheath
Connectivetissue root sheath
Follicle wall
Hair matrix
Melanocyte
Hair papilla
MedullaCortexCuticle
Glassy membrane
Hair root
Longitudinal Section of Base of Follicle
Follicle wall
(c) Diagram of a longitudinal view of the expanded hairbulb of the follicle, which encloses the matrix
Subcutaneousadipose tissue
Figure 5.8c, d
Hair shaft
ArrectorpiliSebaceousgland
Hair root
Hair bulb
(d) Photomicrograph of longitudinal viewof the hair bulb in the follicle (130×)
Internal epithelialroot sheath
External epithelialroot sheath
Connectivetissue root sheath
Hair matrix
Hair papilla
Subcutaneousadipose tissue
MedullaCortexCuticle
Glassy membrane
Hair root
Types and Growth of Hair
• Vellus hairs – body hairs of women and children• Terminal hairs – hair of scalp; axillary and pubic
area (at puberty)• Lanugo
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• Hair thinning and baldness• Due to aging• Male pattern baldness
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Sebaceous Glands
• Occur over entire body, except palms and soles• Secrete sebum – an oily substance
• Simple alveolar glands • Holocrine secretion – entire cell breaks up to form
i
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secretion• Most are associated with a hair follicle• Functions of sebum
• Collects dirt; softens and lubricates hair and skin
Sebaceousgland duct
Hair inhair follicle
Dermalconnectivetissue
Sebaceousgland
Sweatpore
Sebaceous Glands
(a) Photomicrograph of a sectioned sebaceous gland (140×)
Secretory cells
Eccrinegland
Figure 5.9a
Sweatpore
Sweat Glands
(b) Photomicrograph of a sectioned eccrine gland (140×)
Secretory cells
Dermal connectivetissue
Duct
Sebaceousgland
Eccrinegland
Figure 5.9b
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Sweat Glands
• Sweat glands (sudoriferous glands) widely distributed on body
• Sweat – is a blood filtrate • 99% water with some salts
i b li
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• Contains traces of metabolic wastes
Sweat Glands• Two types of sweat gland
• Eccrine gland (merocrine sweat gland) • Most numerous – produce true sweat
• Apocrine gland • Confined to axillary, anal, and genital areas• Produce a special kind of sweat
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Nails
• Nails – scale-like modification of epidermis• Made of hard keratin• Parts of the nail
• Free edgeB d
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• Body• Root• Nail folds• Eponychium – cuticle
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Lateralnail fold
Lunule
(a)
Structure of a Nail
Nailmatrix
Root of nailProximalnail fold
Nail bed Phalanx (bone of fingertip)
Eponychium(cuticle)
Bodyof nail
Free edgeof nail
(b)
Figure 5.7
Burns
• Classified by severity• First degree burn – only epidermis is damaged• Second degree burn – upper part of dermis is also
damaged• Blisters appear
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• Blisters appear• Skin heals with little scarring
• Third degree burn – consume thickness of skin• Burned area appears white, red, or blackened
Estimating Burns Using the Rule of Nines
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Skin Cancer
• Basal cell carcinoma – least malignant and most common
• Squamous cell carcinoma – arises from keratinocytes of stratum spinosum
• Melanoma – a cancer of melanocytes • The most dangerous type of skin cancer
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• The most dangerous type of skin cancer
Skin Cancer
Figure 5.11
The Skin Throughout Life
• Epidermis develops from embryonic ectoderm• Dermis and hypodermis develop from mesoderm• Melanocytes develop from neural crest cells
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14
The Skin Throughout Life
• Fetal skin is well formed after the fourth month• At 5-6 months, the fetus is covered with lanugo
(downy hairs)• Fetal sebaceous glands produce vernix caseosa
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The Skin Throughout Life
• In middle to old age• Skin thins and becomes less elastic• Shows harmful effects of environmental damage• Skin inflammations become more common
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