The Integumentary System Chapter 5 Lecture Notes

1
The Integumentary SystemChapter 5 Lecture Notes

• to accompany
• Anatomy and Physiology From Science to Life
• textbook by
• Gail Jenkins, Christopher Kemnitz, Gerard Tortora

2
Chapter Overview

• 5.1 Skin Composition
• 5.2 Epidermis
• 5.3 Dermis
• 5.4 Skin Color
• 5.5 Accessory Structures of the Skin
• 5.6 Skin Damage and Repair
• 5.7 Functions of Skin

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Essential Terms

• integumentary system
• skin and all of its accessory structures
• hair
• nails
• various glands
• muscles
• nerves
• cutaneous membrane
• another name for skin

4
Introduction

• Skin
• covers the external surface of body
• largest organ of body in surface area and weight
• numerous functions
• temperature regulation
• water repellent
• barrier to external environment
• provide sensory information
• excrete wastes
• synthesizes vitamin D
• protect underlying tissues from UV radiation

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Concept 5.1Skin Composition
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Layers of Integument

• Epidermis
• most superficial
• Dermis
• deep to epidermis
• Hypodermis
• anchors the dermis

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Figure 1.1a
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Figure 1.1b
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Skin Structure

• Two principal parts to skin
• epidermis
• thin
• composed of epithelial tissue
• dermis
• thicker
• composed of connective tissue
• Hypodermis
• deep to dermis but not part of skin
• AKA subcutaneous layer
• areolar and adipose tissues
• fibers from dermis anchor it to hypodermis

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Thin Skin

• covers all parts of body except for palms, palmar
  surfaces of fingers, and soles of feet
• epidermis is thin
• has hair and sebacous glands
• fewer sudoriferous glands than thick skin
• sparcer distribution of sensory receptors

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Thick Skin

• covers palms
• palmar surfaces of fingers
• soles of feet
• thick epidermis
• lacks hair and sebacous glands
• has more sudoriferous glands
• sensory receptors more densely clustered

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Table 5.1
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Concept 5.2 Epidermis
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Epidermis

• composed of keratinized stratified squamous
  epithelium
• four principal types of cells
• keratinocytes
• melanocytes
• Langerhans cells
• Merkel cells

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Figure 5.2a
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Figure 5.2b
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Keratinocytes

• most numerous
• arranged in 4 or 5 layers
• produce keratin
• produce lamellar granules
• waterproofing sealant

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Melanocytes

• found in deepest layer of epidermis
• produce melanin
• pigment that blocks UV radiation
• clusters around nucleus of cells
• long slender projections extend between
  keratinocytes and transfer melanin to them
• melanocytes provide protective melanin to
  keratinocytes but vulnerable to UV radiation
  themselves

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Langerhans cells

• small fraction of epidermal cells
• participate in immunity
• easily damaged by UV radiation

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Merkel Cells

• least numerous of epidermal cells
• located in deepest layer
• contact flattened process of sensory neuron a
  tactile (Merkel) disc
• function together with the disc in sensation of
  touch

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Layers of Epidermis

• Deepest to most superficial
• stratum basale
• stratum spinosum
• statum granulosum
• stratum lucidum (only in thick skin)
• stratum corneum

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Stratum Basale

• single row of cuboidal or columnar keratinocytes
• some are stem cells
• continually undergo cell division
• melanocytes and Merkel cells found scattered here
  also

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Stratum Spinosum

• 8 to 10 layers tightly packed many-sided
  keratinocytes
• most superficial become somewhat flattened
• microscopic preparation shrinks cells
• they pull apart and appear covered with spines
• living cells are rounded and plump, however

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Stratum Granulosum

• middle most layer
• 5 layers of tightly packed many sided
  keratinocytes
• flattened
• undergoing apoptosis
• granules are membrane-enclosed lamellar granules
• release lipid-rich secretion water-repellent

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Stratum Lucidum

• present only in thick skin
• 3 to 5 layers of clear flat dead keratinocytes
• cells contain large amounts of keratin

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Table 5.1
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Stratum Corneum

• most superficial layer
• 25 to 30 layers of dead flat keratinocytes
• continually shed and replaced by cells from
  deeper strata
• interior of cells mostly keratin
• lipids from lamellar granules is between cells
• protects against injury and microbes
• serves as effective water-repellent

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Keratinization and Growth

• cells of stratum basale pushed toward surface as
  new cells appear
• more keratin produced along the way
• takes about 4 weeks in average epidermis

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Table 5.2
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Concept 5.3 Dermis
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Dermis

• deep to epidermis
• composed mainly of connective tissue
• containing collagen and elastic fibers
• embedded in dermis
• blood vessels, nerves, glands, hair follicles
• cells of dermis
• fibroblasts
• macrophages
• adipocytes

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Layers of Dermis

• papillary region
• 1/5th of total dermis
• areolar connective tissue with fine elastic
  fibers
• surface area enhanced by dermal papillae
• contain
• capillary loops
• corpuscles of touch (Meissner corpuscles)
• free nerve endings

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Layers of Dermis

• reticular region
• 80 of dermis
• attached to hypodermis
• consists of denser irregular connective tissue
• collagen fibers and some coarse elastic fibers
• between fibers are
• hair follicles
• nerves
• sebacous glands
• sudoiferous glands
• provides extensibility and elasticity
• extreme stretching of dermis causes striae
  (stretch marks)

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Figure 5.1a
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Figure 5.1b
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Layers of Dermis

• epidermal ridges
• either straight lines or loops
• caused by epidermis projecting into dermis
  between dermal papillae
• increase surface area
• function to increase grip of hands and feet
• glands open on tops of ridges leaving behind
  fingerprints and footprints when smooth objects
  are touched.

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Table 5.3
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Concept 5.4 Skin Color
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Skin color

• Three main pigment producing molecules
• melanin
• carotene
• hemoglobin

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Melanin

• produced by melanocytes
• number of melanocytes same in most people
• activity of melanocytes differs
• exposure to UV light increases production

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Carotene

• precursor of vitamin A
• vitamin A used to synthesize pigments needed for
  vision
• found in stratum corneum and fatty areas lof the
  dermis and hypodermis
• without melanin and carotene, skin appears
  translucent
• European-Americans have pink skin because
  hemoglobin shows through

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Concept 5.5 Accessory Structures of Skin
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Hair

• present on most skin surfaces except palms,
  palmar surfaces of fingers, soles, and plantar
  surfaces of toes
• adults hair most heavily distributed on scalp,
  eyebrows, armpits, and external genitalia
• genetic and hormonal influences determine
  thickness and patterns of distribution
• largely protective functions

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Anatomy of Hair

• composed of columns of dead, keratinized cells
  bonded together by extracellular proteins
• shaft is superficial portion
• transverse section varies
• perfectly rounded straight hair
• oval shaped section wavy hair
• kidney shaped section curly hair

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Anatomy of Hair

• three concentric layers
• inner medulla
• pigment granules and air spaces
• middle cortex
• pigment in dark hair
• mostly air in gray or white hair
• outer cuticle
• single layer of thin, flat, heavily keratinized
  cells
• arranged like shingles on a roof with free edge
  pointing toward end of hair

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Hair Roots

• hair follicle surrounds root of hair
• external root sheath
• downward continuation of epidermis
• internal root sheath
• produced by matrix
• dermal root sheath
• dense dermis surrounding hair follicle
• bulb of hair enlarged at root
• has germinal layer of cells called matrix
• sebacous glands associated with follicle
• arrector pilli muscle makes hair stand on end
• hair root plexuses
• free nerve endings that surround hair follicle
  making dermis sensitive to hair movement

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Figure 5.3a
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Figure 5.3b
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Figure 5.3c
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Figure 5.3d
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Hair Growth

• growth stage
• matrix cells differentiate, keratinize, and die
• forms root sheath and hair shaft
• as new cells areise, hair grows longer
• scalp hair 2 to 6 years
• average 85 of hair in this stage
• resting stage
• old hair is pushed out of follicle
• 3 months

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Hair Color

• melanin produced by melanocytes in matrix of hair
  bulb
• dark hair has true melanin deposited in cells
• blond and red hair have melanin variants with
  more iron and sulfur
• gray hair has less melanin
• white hair has air bubbles and no melanin

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Figure 5.3a
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Figure 5.3b
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Figure 5.3c
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Figure 5.3d
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Glands of Skin

• sebaceous glands
• secrete oil onto shaft of hair or surface of skin
• sudoiferous glands
• secrete sweat
• eccrine or apocrine
• ceruminous glands
• ears
• mammary glands
• breasts

58
Sebaceous Glands

• also known as oil glands
• connected to hair follicles
• secreting portion in dermis
• found everywhere except palms and soles
• secrete sebum
• triglycerides, cholesterol, proteins, inorganic
  salts
• keeps skin soft and pliable, prevents excessive
  water evaporation from skin
• inhibits growth of certain skin bacteria

59
Sudoriferous Glands

• also known as sweat glands
• eccrine
• most common type
• evenly distributed
• most common on forehead, palms, and souls (up to
  450 per square cm)
• secrete sweat with water, ions, urea, uric acid,
  ammonia, amino acids, glucose, and lactic acid
• main function is temperature regulation
• also mimimal participation in waste elimination

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Sudoriferous Glands

• appocrine sweat glands
• less common
• found mainly
• axilla
• groin
• areolae
• bearded region of male faces
• secretory portion in hypodermis
• opens mainly onto hair follicle
• same components as eccrine PLUS lipids and
  proteins
• function begins in puberty
• stimulated during emotional stress and sexual
  excitement

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Sudoriferous Glands

• ceruminous
• secrete cerumen (ear wax)
• found in external auditory canal
• secrete products onto surface of canal or into
  sebaceous glands in ear
• function to provide sticky barrier to impede
  entrance of foreign bodies into ear

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Table 5.4
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Nails

• plates of tightly packed, hard, keratinized
  epidermal cells
• parts
• nail body
• visible portion
• appears pink due to underlying blood capillaries
• lunula near root is white because of thickened
  matrix
• free edge
• extends past finger or nail body
• nail root
• portion buried in fold of skin at base of nail
• matrix with mitotic cells here
• cuticle
• stratum corneum

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Figure 5.4a
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Figure 5.4b
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Concept 5.6 Skin Damage and Repair
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Skin Damage and Repair

• sequence of events that return skin to normal or
  near normal structure and function
• epidermal wound healing
• epidermis only
• deep wound healing
• when dermis is also damaged

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Epidermal Wound Healing

• injury may extend into dermis but not through it
• basal cells (stratum basale cells) at edges of
  wound
• break contact with basement membran
• enlarge
• migrate via mitotic cell division
• stop migrating when contact one another
• contact inhibition
• mitosis then replaces other strata

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Figure 5.5a
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Figure 5.5b
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Figure 5.5c
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Figure 5.5d
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Deep Wound Healing

• injury extends into dermis hypodermis
• scar tissue is formed
• some normal function lost
• occurs in four phases
• inflammatory phase
• migratory phase
• proliferative phase
• maturation phase

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Inflammatory Phase

• blood clot forms loosely uniting wound edges
• inflammation occurs
• eliminates microbes, foreign material, and dying
  tissue
• increases diameter of local blood vessles
• enhancing delivery of nutrients, immune cells,
  and fibroblast

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Migratory Phase

• clot dries into scab
• epithelial cells migrate beneath scab and bridge
  wound
• fibroblasts migrate and lay down collagen fibers
  and glycoproteins in dermis
• new blood vessels grow
• tissue called granulation tissue during this
  phase destined to become scar tissue

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Proliferative Phase

• extensive growth of epithelium
• deposition of collagen in random patterns by
  fibroblasts
• continued growth of blood vessels

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Maturation Phase

• scab sloughs off once epidermis restored to
  normal thickness
• granulation tissue developing into scar tissue
• fibroblasts decrease in number
• blood vessels restored to normal
• scar tissue formation called fibrosis
• elevated scars called
• hypertrophic scars
• if contained within sight of original wound
• keloid scars
• if extended beyond original wound

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Figure 5.5a
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Figure 5.5b
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Figure 5.5c
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Figure 5.5d
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Concept 5.7 Functions of Skin
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Functions of Skin

• thermoregulation
• blood storage
• protection
• cutaneous sensations
• excretion and absorption
• synthesis of calcitrol (vitamin D)

84
Functions of Skin

• thermoregulation
• regulates body temperature
• liberating sweat allowing evaporative cooling of
  blood
• increasing blood flow in dermis
• reducing flow of blood in dermis when cool to
  conserve heat
• blood reservoir
• 8 to 10 of total blood flow in resting adults
  found in dermal blood vessels
• cutaneous sensations
• tactile (touch, pressure, vibration, tickling)
• thermal (warmth and coolness)
• pain (usually indication of impending or actual
  tissue damage)

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Functions of Skin

• protection
• from invasion by microbes
• from abrasion
• from heat
• from chemicals
• from water evaporation through cells
• from influx of water through skin
• sebum and pH of sweat are antimicrobial
• melanin protects from UV radiation
• Langerhans cells are active in immunity
• macrophages phagocytize bacteria and viruses that
  manage to penetrate

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Functions of Skin

• excretion and absorption
• minor role in eliminating wastes
• minor role in absorbing materials from external
  environment
• sweat excretes water, salts, carbon dioxide,
  ammonia and urea
• synthesis of calcitrol
• most active form of vitamin D
• synthesized in response to UV exposure
• aids in absorption of calcium from foods

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End Chapter 5