The Integumentary System Chapter 5 Lecture Notes

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The Integumentary SystemChapter 5 Lecture Notes

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

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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

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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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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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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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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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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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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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Cleavage (Tension) Lines and Striae

• Cleavage (tension) lines elastin and collagen
  fibers oriented in some directions more than in
  others
• Important in surgery
• If incision parallel to lines, there is less
  gapping, faster healing, less scar tissue
• If skin is overstretched, striae (stretch marks)
  occur

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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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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 of 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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Hair Growth

• Growth stage
• Matrix cells differentiate, keratinize, and die
• Forms root sheath and hair shaft
• As new cells arise, 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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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

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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

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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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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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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 membrane
• Enlarge
• Migrate via mitotic cell division
• Stop migrating when contact one another
• Contact inhibition
• Mitosis then replaces other strata

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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 fibroblasts

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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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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)

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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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Burns

• Classifications
• First-degree
• Second-degree
• Third-degree
• Skin Grafts
• Split skin
• Artificial skin
• Cadavers or pigs

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The Rule of Nines

• Used to estimate amount of body that is burned.
• Note differing proportions in adult and child.

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The Rule of Nines
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Aging Effects

• Skin more easily damaged because epidermis thins
  and amount of collagen decreases
• Skin infections more likely
• Wrinkling occurs due to decrease in elastic
  fibers
• Skin becomes drier
• Decrease in blood supply causes poor ability to
  regulate body temperature
• Functioning melanocytes decrease or increase age
  spots
• Sunlight ages skin more rapidly

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End Chapter 5