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 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
• 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
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•
•
•
•
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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
• When the germinal portion of the
epidermis is destroyed, new skin
cannot regenerate with a skin
graft.
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Stratum Spinosum (Figure 5.3b)
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• 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 finger 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 patient’s 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 (Meissner’s 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 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
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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Jaundice
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Jaundice
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Cyanosis
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Erythema
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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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Vitiligo
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Freckles and Liver Spots
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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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Skin color origins
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Pigmented & Non Pigmented Skin
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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 5.4a)
– a root that penetrates the dermis and
subcutaneous layer (Figure 5.4c,d)
– the cuticle (Figure 5.4b), and
– a hair follicle (Figure 5.4c,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
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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.
– Definitive hair stops growing at some length
– Angora hair grows continuously
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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
(Figure 5.1 ).
• 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.
– 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.
– 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 5.5)
• 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 5.5b)
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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
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•
•
•
Abrasion or minor burn
Basal cells migrate across the wound (Figure 5.6a)
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 5.6b).
• 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
5.6c).
– 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 5.6d).
– 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 5.7).
– 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
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•
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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 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 (Figure 5.10).
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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
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