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Chapter 5
The Integumentary System
Principles of Human Anatomy and Physiology, 11e
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INTRODUCTION
• The skin and its accessory structures make up the
integumentary system.
• The integumentary system functions to guard the body’s
physical and biochemical integrity, maintain a constant body
temperature, and provide sensory information about the
surrounding environment.
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Chapter 5
The Integumentary System
• Skin and its accessory
structures
– structure
– function
– growth and repair
– development
– aging
– disorders
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General Anatomy
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•
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•
•
largest organ of the body
composed of all 4 tissue types
22 square feet
1-2 mm thick
Weight 10 lbs.
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STRUCTURE OF THE SKIN
• 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.
– It serves as a 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)
– Contains 4 principle types of cells
– 5 distinct strata (layers) of cells
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Four Principle Cells of the Epidermis
• keratinocytes
– 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
– produce the pigment melanin which contributes to skin
color and absorbs damaging ultraviolet (UV) light
• Langerhans cells
– derived from bone marrow
– participate in immune response
• Merkel cells
– 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:
– 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
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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 & hemidesmosomes
– It’s name indicates its role in
the formation of new cells.
• When the germinal portion of the
epidermis is destroyed, new skin
cannot regenerate with a skin
graft.
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Stratum Spinosum
• 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
• This layer also shows the
formation of a water repellant
sealant between the cells.
• Contain lamellar granules
that release lipid (repels
water).
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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.
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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 patient’s skin after it has grown in culture
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Dermis
• The dermis is composed of connective tissue layer containing
collagen & elastic fibers and has 2 regions.
• 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 (Meissner’s corpuscles), adipose cells,
hair follicles, sebaceous glands, sudoriferous glands
• Finger like projections are called dermal papillae
– anchors epidermis to dermis
– contains capillaries that feed epidermis
– contains Meissner’s 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
– The collagen and elastic fibers provide strength,
extensibility (ability to stretch), and elasticity (ability to
return to original shape after stretching) 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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Tattoos
• Tattooing is a permanent coloration of the skin in which a
foreign pigment is injected into the dermis.
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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.
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Skin Color Pigments
• The wide variety of colors in skin is due to three pigments - melanin,
carotene, and hemoglobin (in blood in capillaries) - in the dermis
• 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 melanin
– vitiligo = autoimmune loss of melanocytes in areas of the skin
produces irregular white patches
• .
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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
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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
– a root that penetrates the dermis and
subcutaneous layer
– the cuticle
– a hair follicle
• 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 (muscles)
– 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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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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Types of hair
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•
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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 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.
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Functions of Hair
• Prevents heat loss
• Decreases sunburn
• Eyelashes help protect eyes
• 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.
• Secretory portion of gland is located in the dermis
– produce sebum which moistens hairs, waterproofs
and softens the skin, and inhibits growth of
bacteria & fungi
• Acne results when glands become inflamed.
– 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.
– Their main purpose is to regulate body temperature through
evaporation (perspiration).
– They also 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.
– secretory portion in dermis
– duct that opens onto hair follicle
– secretions are more viscous
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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.
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Structure of Nails
• Tightly packed keratinized cells over the
dorsal surfaces of the terminal portions
of the fingers and toes.
• Principal parts are the nail body, free
edge, nail root, lunula, eponychium and
the matrix.
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Nail Growth
• Nail matrix is below
nail root -- produces
new cells (growth).
• Functionally, nails help
in grasping and
manipulating small
objects as well as
provide protection
against trama.
• Certain nail conditions
may indicate disease
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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.
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FUNCTIONS OF SKIN -- thermoregulation
• Thermoregulation, the homeostatic control of body
temperature is due to the skin liberating sweat at its surface
and by adjusting the flow of blood in the dermis.
• Perspiration & its evaporation
– lowers body temperature
• 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
• Because the skin has an extensive network of blood
vessels, it functions as a blood reservoir.
• Protection through physical, chemical and biological barriers
– tight cell junctions prevent bacterial invasion
– lipids released retard evaporation
– pigment protects somewhat against UV light
• cutaneous sensations including touch, pressure, vibration,
tickle, heat, cold, and pain arise in the skin
• The skin plays minor roles in excretion, and the passage of
material from the external environment into the body cells.
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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
• Epidermal wounds are repaired by enlargement and
migration of basal cells, contact inhibition and division
of migrating and stationary basal cells.
• Epidermal growth factor stimulates basal cells to
divide and replace the ones that have moved into the
wound.
• 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
– migratory phase
– proliferative phase
– maturation phase
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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.
– 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.
– Scar tissue formation (fibrosis) can occur in deep wound
healing.
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DEVELOPMENT OF THE INTEGUMENTARY
SYSTEM
• Epidermis develops from ectoderm germ layer
– Epidermal derivatives are hair, nails, and skin glands
– The connective tissue and blood vessels associated with
the gland develop from mesoderm.
• Dermis develops from mesenchymal mesodermal germ
layer cells
• The connective tissue and blood vessels associated with the
gland develop from the mesoderm.
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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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AGING AND THE INTEGUMENTARY SYSTEM
• Most effects of aging do not occur until an individual
reaches the late forties.
• Most of the changes occur in the dermis
– Effects of aging are wrinkling, slower growth of hair and
nails, dryness and cracking due to sebaceous gland
atrophy, decrease in melanocytes (gray hair, blotching)
and Langerhans cells (decreased immune response),
and thinner skin as subcutaneous fat is lost.
• Anti-aging treatments diminish the effects of aging. Among
them are microdermabrasion, chemical peel, laser
resurfacing, dermal fillers, Botuliism toxin injection, and non
surgical face lifts.
– Chronic ultraviolet exposure causes photodamage of the
skin. Sun screens and sun blocks help to minimize
photodamage from the sun.
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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 malignant melanoma.
– 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.
• Burns are classified as first-degree and second-degree
(partial-thickness) and third-degree (full thickness).
• The seriousness of a burn is determined by its depth,
extent, and area involved, as well as the person’s 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.
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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 such as a
bed, cast, or splint
– the deficiency of blood flow results in tissue
ulceration.
• Preventable with proper care
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The end!
Test time!!!!!!
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