Chapter 5
The Integumentary System
• Skin and its
accessory structures
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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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Overview
• 2 Major layers of skin
– epidermis is epithelial
tissue only
– dermis is layer of
connective tissue, nerve &
muscle
• Subcutaneous tissue (subQ
or hypodermis) is layer of
adipose & areolar tissue
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– subQ = subcutaneous
injection
– intradermal = within the
skin layer
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Overview of Epidermis
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Stratified squamous epithelium
Contains no blood vessels
4 types of cells
5 distinct strata (layers) of cells
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Cell types of the Epidermis
• Keratinocytes--90%
– produce keratin
• Melanocytes-----8 %
– produces melanin pigment
– melanin transferred to other
cells with long cell processes
• Langerhan cells
– from bone marrow
– provide immunity
• Merkel cells
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– in deepest layer
– form touch receptor with
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sensory neuron
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
• Deepest single layer of cells
• Called stratum germinativum
• Combination of merkel cells,
melanocytes, keratinocytes &
stem cells that divide repeatedly
• Cells attached to each other & to
basement membrane by
desmosomes &
hemidesmosomes
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Stratum Spinosum
• 8 to 10 cell layers held
together by desmosomes
• During slide preparation,
cells shrink and look spiny
• Melanin taken in by
phagocytosis from nearby
melanocytes
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Stratum Granulosum
• 3 - 5 layers of flat dying cells
• Show nuclear degeneration
• Contain dark-staining
keratohyalin granules
• Contain lamellar granules
that release lipid that repels
water
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Stratum Lucidum
• Seen in thick skin on
palms & soles of 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
• Friction stimulates callus
formation
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Keratinization & Epidermal Growth
• Stem cells divide to produce keratinocytes
• As keratinocytes are pushed up towards the
surface, they fill with keratin
• 4 week journey unless outer layers removed in
abrasion
• Hormone EGF (epidermal growth factor) can
speed up process
• Psoriasis = chronic skin disorder
– cells shed in 7 to 10 days as flaky silvery scales
– abnormal keratin produced
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Skin Grafts
• New skin can not regenerate if stratum
basale and its stem cells are destroyed
• Skin graft is covering of wound with piece
of healthy skin
– autograft from self
– isograft from twin
– autologous skin
• transplantation of patients skin grown in culture
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Dermis
• Connective tissue layer composed of collagen &
elastic fibers, fibroblasts, macrophages & fat cells
• Contains hair follicles, glands, nerves & blood
vessels
• Major regions of dermis
– papillary region
– reticular region
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Papillary Region
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Top 20% of dermis
Composed of loose CT & elastic fibers
Finger like projections called dermal papillae
Functions
– anchors epidermis to dermis
– contains capillaries that feed epidermis
– contains Meissner’s corpuscles (touch) & free nerve
endings (pain and temperature)
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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
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increase
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Skin Color Pigments (1)
• Melanin produced in epidermis by melanocytes
– same number of melanocytes in everyone, but differing
amounts of pigment produced
– results vary from yellow to tan to black color
– melanocytes convert tyrosine to melanin
• UV in sunlight increases melanin production
• 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
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Skin Color Pigments (2)
• 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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Skin Color as Diagnostic Clue
• Jaundice
– yellowish color to skin and whites of eyes
– buildup of yellow bilirubin in blood from liver disease
• Cyanotic
– 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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Accessory Structures of Skin
• Epidermal derivatives
• Cells sink inward during
development to form:
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hair
oil glands
sweat glands
nails
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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
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Hair Growth
• 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
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Hair Color
• Result of melanin produced in melanocytes in
hair bulb
• 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
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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
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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
• Secretory portion in the dermis
• Most open onto hair shafts
• Sebum
– combination of cholesterol, proteins, fats & salts
– keeps hair and skin from soft & pliable
– inhibits growth of bacteria & fungi(ringworm)
• Acne
– bacterial inflammation of glands
stimulated
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Sudoriferous (sweat) glands
• Eccrine (sweat) glands
– most areas of skin
– secretory portion in dermis with duct to surface
– regulate body temperature with perspiration
• Apocrine (sweat) glands
– armpit and pubic region
– secretory portion in dermis with duct that opens
onto hair follicle
– secretions more viscous
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Ceruminous glands
• Modified sweat glands produce waxy
secretion in ear canal
• Cerumin contains secretions of oil and wax
glands
• Helps form barrier for entrance of foreign
bodies
• Impacted cerumen may reduce hearing
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Nails
• Tightly packed, keratinized cells
• Nail body is pink due to underlying capillaries
• Lunula appears white due to thickened stratum
basale in that area
• Cuticle (eponychium) is stratum corneum
• Nail matrix deep to the nail root is the region
from which the nail growth occurs
• Growth is 1mm per week--faster in summer &
on most-used hand
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Structure of Nails
• 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 below nail root produces growth
• Cells transformed into tightly packed keratinized cells
• 1 mm per week
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Types of Skin
• Thin skin
– covers most of body
– thin epidermis (.1 to .15 mm.) that lacks stratum
lucidum
– lacks epidermal ridges, has fewer sweat glands and
sensory receptors
• Thick skin
– only on palms and soles
– thick epidermis (.6 to 4.5 mm.) with distinct stratum
lucidum & thick stratum corneum
follicles
and sebaceous glands
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General Functions of the Skin
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Regulation of body temperature
Protection as physical barrier
Sensory receptors
Excretion and absorption
Synthesis of vitamin
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Thermoregulation
• Releasing of sweat onto the skin
– perspiration & its evaporation lowers body
temperature
• Adjusting flow of blood to the body surface
– 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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Protection
• Physical, chemical and biological barrier
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tight cell junctions prevent bacterial invasion
lipids released retard evaporation
pigment protects somewhat against UV light
langerhans cells alert immune system
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Cutaneous Sensations
• Touch, temperature, pressure, vibration,
tickling and some pain sensations arise from
the skin.
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Excretion and Absorption
• Only a minor role is played by the skin
• 400 mL of water evaporates from it daily
• Small amounts salt, CO2, ammonia and
urea are excreted
• Lipid soluble substances can be absorbed
through the skin
– vitamins A, D, E and K, Oxygen and CO2
– acetone and dry-cleaning fluid, lead, mercury,
arsenic, poisons in poison ivy and oak
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Transdermal Drug Administration
• Method by which drugs in a patch enter the
body
• Drug absorption 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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Synthesis of Vitamin D
• Sunlight activates a precursor to vitamin D
• Enzymes in the liver and kidneys transform
that molecule into calcitriol (most active
form of vitamin D)
• Necessary vitamin for absorption of calcium
from food in the gastrointestinal tract
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Epidermal Wound Healing
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Abrasion or minor burn
Basal cells migrate across the wound
Contact inhibition with other cells stops migration
Epidermal growth factor stimulates cell division
Full thickness of epidermis results from further
cell division
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Deep Wound Healing
• If an injury reaches dermis, 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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Phases of Deep Wound Healing
Which phases have been left out of this illustration?
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Development of the Skin
• Epidermis develops from ectodermal germ layer
• Dermis develops from mesodermal germ layer
– at 8 weeks, fetal “skin” is simple cuboidal epithelium
– 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
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called
vernix caseosa is present at birth
Age Related Structural Changes
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Collagen fibers decrease in number & stiffen
Elastic fibers become less elastic
Fibroblasts decrease in number
Langerhans cells and macrophages decrease in
number and become less-efficient phagocytes
• Oil glands shrink and the skin becomes dry
• Walls of blood vessels in dermis thicken so
decreased nutrient availability leads to thinner skin
as subcutaneous fat is lost
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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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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
• 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
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Types of Burns
• First-degree
– only epidermis (sunburn)
• Second-degree burn
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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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Pressure Sores
• Decubitus ulcers
• Caused by constant deficiency of blood
flow to tissue
• Areas affected is skin over bony
prominence in bedridden patients
• Preventable with proper care
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