The Integumentary System

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Chapter 5

• The Integumentary System
• Lecture Outline

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INTRODUCTION

• The skin and its accessory structures make up the
  integumentary system.
• The integumentary system functions to guard the
  bodys physical and biochemical integrity,
  maintain a constant body temperature, and provide
  sensory information about the surrounding
  environment.

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Chapter 5The Integumentary System

• Skin and its accessory structures
• structure
• function
• growth and repair
• development
• aging
• disorders

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General Anatomy

• A large organ composed of all 4 tissue types
• 22 square feet
• 1-2 mm thick
• Weight 10 lbs.

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STRUCTURE OF THE SKIN (Figure 5.1)

• The superficial portion of the skin is the
  epidermis and is composed of epithelial tissue.
• The deeper layer of the skin is the dermis and is
  primarily composed of connective tissue.
• Deep to the dermis is the subcutaneous layer or
  hypodermis. (not a part of the skin)
• It consists of areolar and adipose tissue.
• fat storage, an area for blood vessel passage,
  and an area of pressure-sensing nerve endings.

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Overview of Epidermis

• Stratified squamous epithelium
• avascular (contains no blood vessels)
• 4 types of cells
• 5 distinct strata (layers) of cells

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Four Principle Cells of the Epidermis Figure 5.2

• keratinocytes (Figure 5.2a)
• produce the protein keratin, which helps protect
  the skin and underlying tissue from heat,
  microbes, and chemicals, and lamellar granules,
  which release a waterproof sealant
• melanocytes (Figure 5.2b)
• produce the pigment melanin which contributes to
  skin color and absorbs damaging ultraviolet (UV)
  light
• Langerhans cells (Figure 5.2c)
• derived from bone marrow
• participate in immune response
• Merkel cells (Figure 5.2d)
• contact a sensory structure called a tactile
  (Merkel) disc and function in the sensation of
  touch

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Layers of the Epidermis

• There are four or five layers of the epidermis,
  depending upon the degree of friction and
  mechanical pressure applied to the skin.
• From deepest to most superficial the layers of
  the epidermis are (Figures 5.3 a and b).
• stratum basale (stratum germinativum)
• stratum spinosum
• stratum granulosum
• stratum lucidum (only in palms and soles)
• stratum corneum

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Layers (Strata) of the Epidermis

• Stratum corneum
• Stratum lucidum
• Stratum granulosum
• Stratum spinosum
• Stratum basale

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Stratum Basale (stratum germinativum)

• Deepest single layer of epidermis
• merkel cells, melanocytes, keratinocytes stem
  cells that divide repeatedly
• keratinocytes have a cytoskeleton of
  tonofilaments
• Cells attached to each other to basement
  membrane by desmosomes hemi-desmosomes
• When the germinal portion of the epidermis is
  destroyed, new skin cannot regenerate with a skin
  graft.

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Stratum Spinosum (Figure 5.2a)

• provides strength and flexibility to the skin
• 8 to 10 cell layers are held together by
  desmosomes.
• During slide preparation, cells shrink and appear
  spiny (where attached to other cells by
  desmosomes.)
• Melanin is taken in by keratinocytes (by
  phagocytosis) from nearby melanocytes.

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Stratum Granulosum

• transition between the deeper, metabolically
  active strata and the dead cells of the more
  superficial strata
• 3-5 layers of flat dying cells that show nuclear
  degeneration
• example of apoptosis
• Contain lamellar granules that release lipid that
  repels water
• Contain dark-staining keratohyalin granules
• keratohyalin converts tonofilaments into keratin

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Stratum Lucidum

• present only in the fingers tips, palms of the
  hands, and soles of the feet.
• Three to five layers of clear, flat, dead cells
• Contains precursor of keratin

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Stratum Corneum

• 25 to 30 layers of flat dead cells filled with
  keratin and surrounded by lipids
• continuously shed
• Barrier to light, heat, water, chemicals
  bacteria
• Lamellar granules in this layer make it
  water-repellent.
• Constant exposure to friction will cause this
  layer to increase in depth with the formation of
  a callus, an abnormal thickening of the
  epidermis.

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Keratinization and Growth of the Epidermis

• Stem cells divide to produce keratinocytes
• As keratinocytes are pushed up towards the
  surface, they fill with keratin
• Keratinization is replacement of cell contents
  with the protein keratin occurs as cells move to
  the skin surface over 2-4 weeks.
• Epidermal growth factor (EGF) and other
  hormone-like proteins play a role in epidermal
  growth.
• Table 5.1 presents a summary of the features of
  the epidermal strata.

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Clinical Application

• Psoriasis is a chronic skin disorder
  characterized by a more rapid division and
  movement of keratinocytes through the epidermal
  strata .
• cells shed in 7 to 10 days as flaky silvery
  scales
• abnormal keratin produced
• Skin Grafts
• New skin can not regenerate if stratum basale and
  its stem cells are destroyed
• autograft covering of wound with piece of
  healthy skin from self
• isograft is from twin
• autologous skin
• transplantation of patients skin after it has
  grown in culture

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Dermis (Figure 5.1)

• Connective tissue layer composed of collagen
  elastic fibers, fibroblasts, macrophages fat
  cells
• Contains hair follicles, glands, nerves blood
  vessels
• Two major regions of dermis
• papillary region
• reticular region

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Dermis - Papillary Region

• Top 20 of dermis
• areolar connective tissue containing fine elastic
  fibers, corpuscles of touch (Meissners
  corpuscles), adipose cells, hair follicles,
  sebaceous glands, sudoriferous glands
• The collagen and elastic fibers provide strength,
  extensibility (ability to stretch), and
  elasticity (ability to return to original shape
  after stretching) to skin.
• Finger like projections are called dermal
  papillae
• anchors epidermis to dermis
• contains capillaries that feed epidermis
• contains Meissners corpuscles (touch) free
  nerve endings for sensations of heat, cold, pain,
  tickle, and itch

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Dermis - Reticular Region

• Dense irregular connective tissue
• Contains interlacing collagen and elastic fibers
• Packed with oil glands, sweat gland ducts, fat
  hair follicles
• Provides strength, extensibility elasticity to
  skin
• stretch marks are dermal tears from extreme
  stretching
• Epidermal ridges form in fetus as epidermis
  conforms to dermal papillae
• fingerprints are left by sweat glands open on
  ridges
• increase grip of hand

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Dermis -- Structure

• Epidermal ridges increase friction for better
  grasping ability and provide the basis for
  fingerprints and footprints. The ridges typically
  reflect contours of the underlying dermis.
• Lines of cleavage in the skin indicate the
  predominant direction of the underlying collagen
  fibers. Knowledge of these lines is especially
  important to plastic surgeons.
• Table 5.2 presents a comparison of the structural
  features of the papillary and reticular regions
  of the dermis.

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Tattoos

• Tattooing is a permanent coloration of the skin
  in which a foreign pigment is injected into the
  dermis.

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Basis of Skin Color

• The color of skin and mucous membranes can
  provide clues for diagnosing certain problems,
  such as
• Jaundice
• yellowish color to skin and whites of eyes
• buildup of yellow bilirubin in blood from liver
  disease
• Cyanosis
• bluish color to nail beds and skin
• hemoglobin depleted of oxygen looks purple-blue
• Erythema
• redness of skin due to enlargement of capillaries
  in dermis
• during inflammation, infection, allergy or burns

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Skin Color Pigments

• Melanin produced in epidermis by melanocytes
• melanocytes convert tyrosine to melanin
• UV in sunlight increases melanin production
• same number of melanocytes in everyone, but
  differing amounts of pigment produced
• results vary from yellow to tan to black color
• Clinical observations
• freckles or liver spots melanocytes in a patch
• albinism inherited lack of tyrosinase no
  pigment
• vitiligo autoimmune loss of melanocytes in
  areas of the skin produces white patches
• The wide variety of colors in skin is due to
  three pigments - melanin, carotene, and
  hemoglobin (in blood in capillaries) - in the
  dermis.

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Skin Color Pigments

• Carotene in dermis
• yellow-orange pigment (precursor of vitamin A)
• found in stratum corneum dermis
• Hemoglobin
• red, oxygen-carrying pigment in blood cells
• if other pigments are not present, epidermis is
  translucent so pinkness will be evident

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Accessory Structures of Skin

• develop from the embryonic epidermis
• Cells sink inward during development to form
• hair
• oil glands
• sweat glands
• nails

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HAIR

• Hairs, or pili, are present on most skin surfaces
  except the palms, palmar surfaces of the digits,
  soles, and plantar surfaces of the digits.
• Hair consists of
• a shaft above the surface (Figure 5.5a)
• a root that penetrates the dermis and
  subcutaneous layer (Figure 5.5c,d)
• the cuticle (Figure 5.5b), and
• a hair follicle (Figure 5.5c,d).
• New hairs develop from cell division of the
  matrix in the bulb.

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Structure of Hair

• Shaft -- visible
• medulla, cortex cuticle
• CS round in straight hair
• CS oval in wavy hair
• Root -- below the surface
• Follicle surrounds root
• external root sheath
• internal root sheath
• base of follicle is bulb
• blood vessels
• germinal cell layer

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Structure of Hair

• Shaft -- visible
• medulla, cortex cuticle
• CS round in straight hair
• CS oval in wavy hair
• Root -- below the surface
• Follicle surrounds root
• external root sheath
• internal root sheath
• base of follicle is bulb
• blood vessels
• germinal cell layer

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Structure of Hair

• Shaft -- visible
• medulla, cortex cuticle
• CS round in straight hair
• CS oval in wavy hair
• Root -- below the surface
• Follicle surrounds root
• external root sheath
• internal root sheath
• base of follicle is bulb
• blood vessels
• germinal cell layer

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Hair Related Structures

• Arrector pili
• smooth muscle in dermis contracts with cold or
  fear.
• forms goosebumps as hair is pulled vertically
• Hair root plexus
• detect hair movement
• sebaceous (oil) glands

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Types of hair

• Lanugo is a fine, nonpigmented hair that covers
  the fetus.
• Vellus hair is a short, fine hair that replaces
  lanugo
• Course pigmented hair appears in response to
  androgens
• Hair that appears in response to androgens and
  hair of the head, eyelashes and eyebrows is known
  as terminal hair.

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Hair removal

• Depilatories dissolve the protein in the hair
  shaft
• Electrolysis uses an electric current to destroy
  the hair matrix.

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Hair Growth

• The hair growth cycle consists of a growing stage
  and a resting stage.
• Growth cycle growth stage resting stage
• Growth stage
• lasts for 2 to 6 years
• matrix cells at base of hair root producing
  length
• Resting stage
• lasts for 3 months
• matrix cells inactive follicle atrophies
• Old hair falls out as growth stage begins again
• normal hair loss is 70 to 100 hairs per day
• Both rate of growth and the replacement cycle can
  be altered by illness, diet, high fever, surgery,
  blood loss, severe emotional stress, and gender.
• Chemotherapeutic agents affect the rapidly
  dividing matrix hair cells resulting in hair loss.

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Hair Color

• Hair color is due primarily to the amount and
  type of melanin.
• Graying of hair occurs because of a progressive
  decline in tyrosinase.
• Dark hair contains true melanin
• Blond and red hair contain melanin with iron and
  sulfur added
• Graying hair is result of decline in melanin
  production
• White hair has air bubbles in the medullary shaft
• Hormones influence the growth and loss of hair
  (Clinical applications).

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Functions of Hair

• Prevents heat loss
• Decreases sunburn
• Eyelashes help protect eyes
• Touch receptors (hair root plexus) senses light
  touch

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Glands of the Skin

• Specialized exocrine glands found in dermis
• Sebaceous (oil) glands
• Sudiferous (sweat) glands
• Ceruminous (wax) glands
• Mammary (milk) glands

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Sebaceous (oil) glands

• Sebaceous (oil) glands are usually connected to
  hair follicles they are absent in the palms and
  soles (Figures 5.1 and 5.6a).
• Secretory portion of gland is located in the
  dermis
• produce sebum
• contains cholesterol, proteins, fats salts
• moistens hairs
• waterproofs and softens the skin
• inhibits growth of bacteria fungi (ringworm)
• Acne
• bacterial inflammation of glands
• secretions are stimulated by hormones at puberty

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Sudoriferous (sweat) glands

• Eccrine sweat glands have an extensive
  distribution most areas of skin
• secretory portion is in dermis with duct to
  surface
• ducts terminate at pores at the surface of the
  epidermis (Figure 5.6b).
• regulate body temperature through evaporation
  (perspiration)
• help eliminate wastes such as urea.
• Apocrine sweat glands are limited in distribution
  to the skin of the axilla, pubis, and areolae
  their duct open into hair follicles (Figure
  5.6c).
• secretory portion in dermis
• duct that opens onto hair follicle
• secretions are more viscous
• Table 5.3 compares eccrine and apocrine sweat
  glands.

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Ceruminous Glands

• Ceruminous glands are modified sudoriferous
  glands that produce a waxy substance called
  cerumen.
• found in the external auditory meatus
• contains secretions of oil and wax glands
• barrier for entrance of foreign bodies
• An abnormal amount of cerumen in the external
  auditory meatus or canal can result in impaction
  and prevent sound waves from reaching the ear
  drum (Clinical Application).

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Structure of Nails (Figure 5.7)

• Tightly packed keratinized cells
• Nail body
• visible portion pink due to underlying
  capillaries
• free edge appears white
• Nail root
• buried under skin layers
• lunula is white due to thickened stratum basale
• Eponychium (cuticle)
• stratum corneum layer

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Nail Growth

• Nail matrix is below nail root -- produces growth
• Cells transformed into tightly packed keratinized
  cells
• 1 mm per week
• Certain nail conditions may indicate disease
  (Figure 5.8)

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TYPES OF SKIN

• Thin skin
• covers all parts of the body except for the palms
  and palmar surfaces of the digits and toes.
• lacks epidermal ridges
• has a sparser distribution of sensory receptors
  than thick skin.
• Thick skin (0.6 to 4.5 mm)
• covers the palms, palmar surfaces of the digits,
  and soles
• features a stratum lucidum and thick epidermal
  ridges
• lacks hair follicles, arrector pili muscles, and
  sebaceous glands, and has more sweat glands than
  thin skin.
• Table 5.4 summarizes the fractures of thin and
  thick skin.

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FUNCTIONS OF SKIN -- thermoregulation

• Perspiration its evaporation
• lowers body temperature
• flow of blood in the dermis is adjusted
• Exercise
• in moderate exercise, more blood brought to
  surface helps lower temperature
• with extreme exercise, blood is shunted to
  muscles and body temperature rises
• Shivering and constriction of surface vessels
• raise internal body temperature as needed

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FUNCTIONS OF SKIN

• blood reservoir
• extensive network of blood vessels
• protection - physical, chemical and biological
  barriers
• tight cell junctions prevent bacterial invasion
• lipids released retard evaporation
• pigment protects somewhat against UV light
• Langerhans cells alert immune system
• cutaneous sensations
• touch, pressure, vibration, tickle, heat, cold,
  and pain arise in the skin

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FUNCTIONS OF SKIN

• Synthesis of Vitamin D
• activation of a precursor molecule in the skin by
  UV light
• enzymes in the liver and kidneys modify the
  activated molecule to produce calcitriol, the
  most active form of vitamin D.
• necessary vitamin for absorption of calcium from
  food in the gastrointestinal tract
• excretion
• 400 mL of water/day, small amounts salt, CO2,
  ammonia and urea

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Transdermal Drug Administration

• method of drug passage across the epidermis and
  into the blood vessels of the dermis
• drug absorption is most rapid in areas where skin
  is thin (scrotum, face and scalp)
• Examples
• nitroglycerin (prevention of chest pain from
  coronary artery disease)
• scopolamine ( motion sickness)
• estradiol (estrogen replacement therapy)
• nicotine (stop smoking alternative)

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MAINTAINING HOMEOSTASIS SKIN WOUND HEALING
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Epidermal Wound Healing

• Abrasion or minor burn
• Basal cells migrate across the wound (Figure
  5.9a)
• Contact inhibition with other cells stops
  migration
• Epidermal growth factor stimulates basal cells to
  divide and replace the ones that have moved into
  the wound (Figure 5.9b).
• Full thickness of epidermis results from further
  cell division

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Deep Wound Healing

• When an injury extends to tissues deep to the
  epidermis, the repair process is more complex
  than epidermal healing, and scar formation
  results.
• Healing occurs in 4 phases
• inflammatory phase has clot unite wound edges and
  WBCs arrive from dilated and more permeable blood
  vessels
• migratory phase begins the regrowth of epithelial
  cells and the formation of scar tissue by the
  fibroblasts
• proliferative phase is a completion of tissue
  formation
• maturation phase sees the scab fall off
• Scar formation
• hypertrophic scar remains within the boundaries
  of the original wound
• keloid scar extends into previously normal tissue
• collagen fibers are very dense and fewer blood
  vessels are present so the tissue is lighter in
  color

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Deep Wound Healing

• Phases of Deep Wound Healing
• During the inflammatory phase, a blood clot
  unites the wound edges, epithelial cells migrate
  across the wound, vasodilatation and increased
  permeability of blood vessels deliver phagocytes,
  and fibroblasts form (Figure 5.9c).
• During the migratory phase, epithelial cells
  beneath the scab bridge the wound, fibroblasts
  begin scar tissue, and damaged blood vessels
  begin to grow. During this phase, tissue filling
  the wound is called granulation tissue.

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Phases of Deep Wound Healing
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Deep Wound Healing

• Phases of Deep Wound Healing
• During the proliferative phase, the events of the
  migratory phase intensify.
• During the maturation phase, the scab sloughs
  off, the epidermis is restored to normal
  thickness, collagen fibers become more organized,
  fibroblasts begin to disappear, and blood vessels
  are restored to normal (Figure 5.9).
• Scar tissue formation (fibrosis) can occur in
  deep wound healing.

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DEVELOPMENT OF THE INTEGUMENTARY SYSTEM

• Epidermis develops from ectodermal germ layer
• Hair, nails, and skin glands are epidermal
  derivatives (Figure 5.10a).
• The connective tissue and blood vessels
  associated with the gland develop from mesoderm.
• Dermis develops from mesenchymal mesodermal germ
  layer cells

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Development of the Skin

• Timing
• at 8 weeks, fetal skin is simple cuboidal
• nails begin to form at 10 weeks, but do not reach
  the fingertip until the 9th month
• dermis forms from mesoderm by 11 weeks
• by 16 weeks, all layers of the epidermis are
  present
• oil and sweat glands form in 4th and 5th month
• by 6th months, delicate fetal hair (lanugo) has
  formed
• Slippery coating of oil and sloughed off skin
  called vernix caseosa is present at birth

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Age Related Structural Changes

• Collagen fibers decrease in number stiffen
• Elastic fibers become less elastic
• Fibroblasts decrease in number
• decrease in number of melanocytes (gray hair,
  blotching)
• decrease in Langerhans cells (decreased immune
  responsiveness)
• reduced number and less-efficient phagocytes

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AGING AND THE INTEGUMENTARY SYSTEM

• Most of the changes occur in the dermis
• wrinkling, slower growth of hair and nails
• dryness and cracking due to sebaceous gland
  atrophy
• Walls of blood vessels in dermis thicken so
  decreased nutrient availability leads to thinner
  skin as subcutaneous fat is lost.
• anti-aging treatments
• microdermabrasion, chemical peel, laser
  resurfacing, dermal fillers, Botuliism toxin
  injection, and non surgical face lifts.
• Sun screens and sun blocks help to minimize
  photodamage from ultraviolet exposure

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Photodamage

• Ultraviolet light (UVA and UVB) both damage the
  skin
• Acute overexposure causes sunburn
• DNA damage in epidermal cells can lead to skin
  cancer
• UVA produces oxygen free radicals that damage
  collagen and elastic fibers and lead to wrinkling
  of the skin

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DISORDERS HOMEOSTATIC IMBALANCES

• Skin cancer can be caused by excessive exposure
  to sunlight.
• Among the risk factors for skin cancer are skin
  type, sun exposure, family history, age, and
  immunologic status.
• The three most common forms are
• basal cell carcinoma,
• squamous cell carcinoma, and
• malignant melanoma.

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Skin Cancer

• 1 million cases diagnosed per year
• 3 common forms of skin cancer
• basal cell carcinoma (rarely metastasize)
• squamous cell carcinoma (may metastasize)
• malignant melanomas (metastasize rapidly)
• most common cancer in young women
• arise from melanocytes ----life threatening
• key to treatment is early detection watch for
  changes in symmetry, border, color and size
• risks factors include-- skin color, sun exposure,
  family history, age and immunological status

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Burns

• Tissue damage from excessive heat, electricity,
  radioactivity, or corrosive chemicals that
  destroys (denatures) proteins in the exposed
  cells is called a burn.
• Generally, the systemic effects of a burn are a
  greater threat to life than are the local
  effects.
• The seriousness of a burn is determined by its
  depth, extent, and area involved, as well as the
  persons age and general health. When the burn
  area exceeds 70, over half of the victims die.

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Burns

• Destruction of proteins of the skin
• chemicals, electricity, heat
• Problems that result
• shock due to water, plasma and plasma protein
  loss
• circulatory kidney problems from loss of plasma
• bacterial infection
• Two methods for determining the extent of a burn
  are the rule of nines and the Lund-Bowder method
  (Figure 5.13).

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Burns
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Types of Burns

• First-degree
• only epidermis (sunburn)
• Second-degree burn
• destroys entire epidermis part of dermis
• fluid-filled blisters separate epidermis dermis
• epidermal derivatives are not damaged
• heals without grafting in 3 to 4 weeks may scar
• Third-degree or full-thickness
• destroy epidermis, dermis epidermal derivatives
• damaged area is numb due to loss of sensory nerves

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Burns
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Pressure Sores

• Pressure ulcers, also known as decubitus ulcers
• caused by a constant deficiency of blood to
  tissues overlying a bony projection that has been
  subjected to prolonged pressure
• typically occur between bony projection and hard
  object such as a bed, cast, or splint
• the deficiency of blood flow results in tissue
  ulceration.
• Preventable with proper care

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• end