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Chapter 6
Skin and the Integumentary
System
• Composed of several tissues
• Maintains homeostasis
• Protective covering
• Retards water loss
• Regulates body temperature
• Houses sensory receptors
• Contains immune system cells
• Synthesizes chemicals
• Excretes small amounts of waste
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Physiology of Skin
• Regulate body temperature
– Sweat & change of blood flow toward surface of skin
• Protection
– From abrasions, bacteria, dehydration, and ultra violet
radiation
• Reception of Stimuli
– Nerve endings specifically designed for pressure,
temperature, touch and pain
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Physiology of Skin
• Excretion
– sweat helps reduce levels of water, salts, and other
organic compounds
• Synthesis of Vitamin D
– Helps manufacture vitamin D
– Helps body absorb calcium and phosphorus from food
• Immunity
– Certain cells help in your ability to produce antibodies
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Skin Cells
• Help produce Vitamin D needed for
normal bone and tooth development
• Some cells (keratinocytes) produce
substances that simulate development of
some WBCs
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Layers of Skin
• Epidermis
• Dermis
• Subcutaneous layer
• beneath dermis
• not part of skin
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Subcutaneous Layer
• hypodermis
• loose connective tissue
• adipose tissue
• insulates
• major blood vessels
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Epidermis
• lacks blood vessels
• keratinized
• thickest on palms and soles (0.8-1.4mm)
• melanocytes provide melanin
• rests on basement membrane
• stratified squamous
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Epidermal Cells
• Keratinocyte
– Produce keratin (protein)
• Melanocyte
– Found at base of epidermis
– Produces melanin
• Responsible for skin color and absorption of UV
radiation
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Epidermal Cells
• Langerhan’s cells
– Interact with helper T-cells of the immune
system
• Granstein cells
– Resistant to UV radiation
– Interact with other T-cells of immune system
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Epidermis
Layers of Epidermis
• stratum corneum
• stratum lucidum
• stratum granulosum
• stratum spinosum
• stratum basale
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Epidermal Layers
• Stratum Basale
– Deepest layer
– Single layer of cells capable of continued cell
division
– Also called the stratum germinativum
– Cells may migrate to the dermis to become glands
and hair follicles
– Areas with no hair contain nerve endings that are
sensitive to touch (tactile disc)
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Epidermal Layers
• Stratum Spinosum
– 8 to 10 rows of close fitting cells
– Surface of the cells contain spine-like projections
that help to join cells together
• Stratum Granulosum
– 3 to 5 rows flattened cells that contain dark stained
granules of keratohyalin, which is involved in the
first steps of keratin formation
– Cells start to die in this layer
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Epidermal Layers
• Stratum Lucidum
– Found only in thick skin of palms, and the
soles of your feet
– 3 to 5 rows of clear, flat, dead cells
• Stratum Corneum
– 25 to 30 rows of keratinized cells
– Continuously replaced and shed
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Dermis
• on average 1.0-2.0mm thick
• contains dermal papillae
• binds epidermis to underlying
tissues
• irregular dense connective tissue
• muscle cells
• nerve cell processes
• specialized sensory receptors
• blood vessels
• hair follicles
• glands
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Dermal Layers
• Papillary Layer
– Upper 1/5 of the dermis
– Dermal papillae
• Finger-like projections that increase surface area
• Projections that extend into the epidermis and may contain
blood vessels or
• Meissner’s corpuscles- endings that are sensitive to touch
• Cause ridges in the overlying epidermis (fingerprints)
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Dermal Layers
• Reticular layer
– Formed by closely packed irregularly arranged
connective tissue
– Glands, hair, and nerves fill spaces between
– Provides the skin with its strength and elasticity
– Attached to underlying organs by the subcutaneous
layer
– Pacinian Corpuscles
• Located in the subcutaneous layer
• Nerve endings that are sensitive to pressure
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Hair Follicles
• epidermal cells
• tube-like depression
• extends into dermis
• hair root
• hair shaft
• hair papilla
• dead epidermal cells
• melanin
• arrector pili muscle
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Hair
• Protects, guards scalp from the sun, eyes
from foreign particles
• Hair in the ear and nose protect these
structures from foreign particles and
insects that might be inhaled or crawl
into the ear
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Anatomy of the Hair
• Shaft
– Superficial portion that most of which projects
above the skin
– Made up of 3 parts
• Medulla
– inner portion that contains air spaces
• Cortex
– Middle portion that makes the majority of the hair shaft
– Contains pigment granules of dark hair & mostly air in light
hair
• Cuticle
– Outer most layers
– Cells heavily keratinized
– Arranged like upside-down shingles
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Anatomy of the Hair
• Root
– Portion that penetrates the dermis and even the
subcutaneous layer
– Contains the 3 portions like the shaft
• Hair follicle
– Surrounds the root
– Continuation of the stratum basale and stratum
spinosum layers of the epidermis
– Base of each follicle enlarges and looks like an onion
shaped bulb
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Anatomy of the Hair
• Papillae of the hair
– Indentation of the bulb that is filled with
loose connective tissue and many blood
vessels
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Associates of the Hair Complex
• Sebaceous (oil) glands
– Found in association with hair follicles except on the
lips and eyelids
– Secrete sebum
• Mixture of fats, cholesterol, proteins, and inorganic salts
– Function
• Prevents hair from becoming brittle
• Forms a film that prevents excess evaporation of water
from the skin
• Keeps the skin soft and flexible
• Inhibits the growth of certain bacteria
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Sebaceous Glands
• usually associated with hair
follicles
• holocrine glands
• secrete sebum
• absent on palms and
soles
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Clinical Application:
Sebaceous Glands
• Blackheads
– Sebaceous glands enlarge due to
accumulated sebum
– Color of blackhead is due to melanin and
oxidized oil, not dirt
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Associates of the Hair Complex
• Sudoriferous Glands
– Divided on basis of structure and location
– 3 types
• Apocrine
–
–
–
–
Located in axilla and pubic region
Excretory duct open to hair follicles
Start to function at the onset of puberty
Emit an odor
• Eccrine
– More common
– Ducts open to the surface of the skin
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Associates of the Hair Complex
• Both Apocrine and Eccrine glands secrete:
– Perspiration
• mixture of water, salts (NaCl), urea, uric acid, amino acids,
ammonia, sugar, lactic acid and ascorbic acid
• Function:
– Reduces body temperature by evaporation
– Elimination of waste
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Sweat Glands
• sudoriferous glands
• widespread in skin
• originates in deeper
dermis or hypodermis
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Associates of the Hair Complex
• Mammary glands
– Modified sudoriferous glands
– Reproductive unit
• Ceruminous glands
– Found in external auditory meatus
– Produce ear wax that protect your ears from
foreign particles
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Nails
• protective coverings
• nail plate/nail body
• nail bed
• lunula
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Nails
• Average growth is about 1 mm per week
• Protect the end of the digits and aid the
manipulation of small objects
• 4 parts of the nail
– Free edge- extends past distal end of the digit
– Body- majority of the visible nail
• Lunula- semilunar white part of the body
– Nail Root- hidden part of the nail that lies above the
nail matrix
– Nail Matrix- functions to bring the growth of nails
• when superficial cells become nail cells, push the whole
nail across the nail bed
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Regulation of Body
Temperature
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Problems in Temperature
Regulation
Hyperthermia – abnormally high body temperature
Hypothermia – abnormally low body temperature
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Skin Color
Genetic Factors
Physiological Factors
• varying amounts of
• dilation of dermal blood
melanin
vessels
• varying size of melanin
• constriction of dermal blood
granules
vessels
• albinos lack melanin
• accumulation of carotene
• jaundice
Environmental Factors
• sunlight
• UV light from sunlamps
• X rays
• darkens melanin
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Skin Color
• Melanin
– Pigment found primarily in the basale and
spinosum epidermal layers
– Varies skin color from yellow to black
– Number of melanocytes about the same for
all races
– Skin color due to amount of pigment
melanocytes produce
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Skin Conditions
• Albinism
– inability to produce melanin
• Vitiligo
– loss of melanocytes from an area of skin
• Freckles
– patches of melanin
• Tanning
– Also associated with the melanin
– Ultra-violet radiation increases melanocyte activity
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Skin Color
• Carotene
– Found in the stratum corneum
– People of Asian origin have carotene in fatty
areas of the dermis
– Gives a yellowish hue to the skin
• Capillaries
– cause the skin to have a pink appearance
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Epidermal Wound Healing
• Common skin wounds
– Abrasions
• portions of the skin has been scraped away
– Laceration
• irregular tear of the skin
– Puncture
• hole “popped” through the skin
– Incisions
• clean out through the skin
– Contusion (bruise)
• Tissue below skin damaged
• skin is not broken
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Epidermal Wound Healing
•
Superficial Wound Healing
1. Basale cells in the area of the wound break
contact with the basement membrane that
connects the epidermis to the dermis
2. Basale cells enlarge and migrate across the
wound
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Epidermal Wound Healing
3. Contact inhibition stops the migrating cells
and turns cells in a new direction continues
until cells are surrounded by similar cells
–
Malignant (cancer) cells don’t follow the
same rules
•
continue to spread and invade other areas
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Epidermal Wound Healing
4. When the “floor” of the wound is
covered
• Cells divide to form new strata (layers)
• This thickens the epidermis and fills in the
wound from the bottom upward
5. If a scab was formed, it will fall off
when the new epidermis is thick enough
to protect itself
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Healing of Cuts
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Deep Wound Healing
• When the injury extends past the
epidermis
• Commonly due to accidental lacerations
of surgical incisions
• Scar formation will occur
• Repair more complex (4 stages)
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Deep Wound Healing
1. Inflammatory phase
–
–
–
–
Inflammationvascular and cellular
response to rid wound
of dirt, infection, etc
Blood clot forms to
keep the edges of the
wound close together
Epidermal cells start
to migrate
Vasodilation floods the
areas with phagocytic
cells and fibroblast
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Deep Wound Healing
2. Migratory phase
•
•
•
Clot becomes scab and
epithelial cells continue
migrating to bridge the
wound
Fibroblast synthesize
scar tissue
Damaged blood vessels
begin to re-grow
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Deep Wound Healing
3. Proliferative Phase
– Epithelial cells grow
under the scab
– Collagenous scar
tissue is deposited
– Continued blood
vessel growth
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Deep Wound Healing
4. Maturation Phase
• Scab falls off
• Collagenous fibers
become more organized
• Blood vessels restored to
normal
• Scar tissue
• Dense blood vessels
• May not contain hair,
glands, or sensory
receptors
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Healing of Burns
• First degree burn
– superficial partialthickness
– Dermal blood vessels
dilate causing skin to
warm and redden
– Mild edema (swelling)
– Surface layer sometimes
shed
– Heals in a few days to 2
weeks
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decompressor
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Healing of Burns
• Second degree burn
– deep partial-thickness
– Damages epidermis and
some dermis
– Fluid escapes damaged
capillaries causing blisters
– Healing depends on stem
cells derived from
epidermis but located
deep within dermis
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Healing of Burns
• Third degree burn
– full-thickness
– Skin becomes dry, leathery
– Red, black, white color
– autograft
• Thin layer of skin taken from unburned area & transplanted
– homograft
• Cadaver skin used to cover burn
• Temporary for protection of underlying tissue and prevents infection
– various skin substitutes
• Amniotic membrane
• Artificial membranes composed of silicone, polyurethane, or nylon
• Cultured epithelial cells
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Healing of Burns
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Rule of Nines
• Divides skin surface into regions, each
accounting for 9% (or some multiple of
9%) of the total surface area
• Important for planning to replace body
fluids and electrolytes
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Rule of Nines
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Life Span Changes
• Skin becomes scaly
• Age spots appear
• Epidermis thins
• Dermis becomes reduced
• Loss of fat
• Wrinkling
• Sagging
• Sebaceous glands secrete
less oil
• Melanin production slows
• Hair thins
• Number of hair follicles
decrease
• Nail growth becomes impaired
• Sensory receptors decline
• Body temperature unable to be
controlled
• Diminished ability to activate
Vitamin D
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Clinical Application
• Maglignant Melanoma
– Cancer of the melanocytes
– Often caused from
overexposure to ultraviolet light of the sun
– Most tumors involve
basale cells, so they can be
removed surgically
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Clinical Application
• Malignant Melanoma
– Best treatment is prevention
– Examine your skin for moles that develop
irregular appearance
– Uneven surfaces or a mixture of colors or
change in size or start to bleed
– Many of these may be a sign of developing
melanoma
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Clinical Application
• Wrinkles
– Collagen fibers
• stiffens, break apart and
form a shapeless tangle
– Elastic Fibers
• some elasticity, thicken
and fray
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– Subcutaneous
• decreases
– Sebaceous glands
• atrophy leads to dry,
cracked skin
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Clinical Application
• Melanocytes
– Decrease of functioning melanocytes lead to gray
hair and atypical skin pigmentation
– Increase of size of some melanocytes can cause liver
spots
– Older skin is more susceptible to pathological
conditions like cancer and senile pruritis (itching)
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Clinical Application
Acne Vulgaris
•most common skin disorder
•sebum and epithelial cells clog glands
•produces whiteheads and blackheads (comedones)
•anaerobic bacteria trigger inflammation (pimple)
•largely hormonally induced
•androgens stimulate sebum production
•treatments include antibiotics, topical creams, birth control pills
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Clinical Application
• Cystic Acne
– Scarring as a result of
severe acne
– Surrounding epidermal
cells might be replaced by
connective tissue
– Squeezing, pinching or
scratching the lesion will
increase the chance of
developing cystic acne
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Clinical Application
• Psoriasis
– Symptoms are distinct,
reddish, small round skin
elevations covered with
scales
– Caused by abnormally
high rate of epidermal cell
mitosis
– Trauma, infection, stress,
seasonal or hormonal
changes can irritate
– Treatments include
steroid ointments and
natural sunlight (ultraviolet light)
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Clinical Application
• Sunburn
– Dead layers of cells
peel off and leave
unprotected layers of
cells
– Ultra-violet rays of
sunlight damage the
cells’ DNA and RNA
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