1. health and fitness
2. aging

Chapter
5
The
Integumentary
System
Copyright © 2010 Pearson Education, Inc.
Introduction to the Integumentary System
• The integumentary system consists of skin, hair, nails, and various glands
– The integument is the largest system of the body
• 16% of body weight
• 1.5 to 2 m2 in area
– The integument is made up of two parts:
• Cutaneous membrane (skin)
• Superficial epithelium called epidermis
• Underlying connective tissue called dermis
• Subcutaneous layer (hypodermis) made of loose connective
tissue attaches integument to deeper structures (muscle, bone)
• Hypodermis is not
considered part of
integumentary system
• Location of
“hypodermic” injections
• Accessory structures –
originate in dermis and extend
through epidermis to skin
surface
• Include hair, nails, and glands
Functions of Integument
• The integument has 5 major functions:
– Protection: covers and protects underlying tissues and organs from
impacts, chemicals, and infections
• Also prevents loss of body fluids
– Temperature Maintenance: skin maintains normal body temperature
by regulating heat exchange with environment (insulation and
evaporation)
– Synthesis and Storage of Nutrients: epidermis makes vitamin D3
(aids in calcium uptake)
• Dermis also stores large reserves of lipids in adipose tissue
– Sensory Reception: receptors detect touch, pressure, pain, and
temperature
• This information is then relayed to nervous system
– Excretion and Secretion: integumentary glands excrete salts, water,
and organic wastes
• Specialized glands of breasts secrete milk
5-1 The epidermis is
composed of strata (layers)
with various functions
Epidermis
• Epidermis consists of stratified squamous epithelium
containing several different cell layers
– Thick skin: contains 5 layers of cells (keratinocytes)
• Found on palms of hands and soles of feet
• Thickness of ~ 0.5mm (paper towel)
– Thin skin: contains 4 layers of keratinocytes
• Covers the rest of the body
• Thickness of ~0.08mm (wall of plastic sandwich bag)
• Epidermis is avascular
– Nutrients and oxygen diffuse from capillaries in the dermis
Epidermis
• Structures of the Epidermis
– The five strata of keratinocytes in thick skin
– From basal lamina to free surface:
• Stratum germinativum
• Stratum spinosum
• Stratum granulosum
• Stratum lucidum
• Stratum corneum
Stratum Germinativum
• Deepest epidermal layer is called the stratum germinativum (or stratum
basale)
– Hemidesmosomes attach this layer to basement membrane
• Basement membrane separates epidermis from loose connective
tissue of dermis
– Form epidermal ridges that extend into dermis
• Dermal projections called dermal papillae extend upward between
adjacent ridges
– Increase surface area for diffusion of nutrients between dermis
and epidermis
• Contours of skin follow ridge patterns
– Ex) Form complex whorls
in thick skin that make up
fingerprints
» Increases surfaces
area of skin
» Increases friction to
ensure secure grip
Stratum Germinativum
• Stratum germinativum is the layer where new cells are generated and
begin to grow (“germinative layer”)
– Has many germinative (stem) cells
• Division of these cells replace cells that are lost or shed at
epithelial surface
– Also contains melanocytes
• Cells that have cytoplasmic processes extend between
epithelial cells
– Synthesize melanin, the brown, yellow-brown, or black
pigment that colors skin
– Receptors in this layer also provide information about objects
touching the skin
Intermediate Strata
• Intermediate strata include 3 layers
– 2nd layer of epidermis is called the stratum spinosum (the “spiny layer”):
– Produced by division stem cells in stratum germinativum
– Contains 8-10 layers of keratinocytes bound by desmosomes
» Accumulation of desmosomes causes cells to shrink until
cytoskeletons stick out (spiny)
» Cells also begin to synthesize keratin in this layer
– 3rd layer of epidermis is called the stratum granulosum (the “grainy
layer”)
• Consists of cells displaced from stratum spinosum
• Cells in this layer have stopped dividing
– Begin making large amounts of the protein keratin
» Keratin is extremely durable and water-resistant
» Coats surface of skin and forms basic structure of hair,
calluses, and nails
» Also forms horns, hooves, and feathers
– 4th layer of epidermis is called stratum lucidum (the “clear layer”)
• Found only in thick skin of palms and soles
• Contains flattened, densely-packed cells filled with keratin
Stratum Corneum
• The most superficial layer of epidermis is called the stratum
corneum (the “horn layer”)
– Consists of 15-30 layers of flattened and dead cells with large
amounts of keratin (keratinized or cornified cells)
• These cells remain tightly connected by desmosomes
– Cells are therefore shed
in large groups or sheets
rather than individually
– Surface of stratum corneum is
dry and waterproof
• Unsuitable for growth of many
microorganisms
Skin Life Cycle
• It takes 2-4 weeks for cells to move from stratum
germinativum to stratum corneum
– Cells die as they are displaced from oxygen and nutrients
• Also become increasingly packed with keratin as they move
– Dead cells usually remain in stratum corneum for 2
additional weeks before they are shed
• Replaced by new layers arriving from underlying strata as these
superficial layers are lost
– Occurs on all exposed skin surfaces except eyes
5-2 Factors influencing skin color
are epidermal pigmentation and
dermal circulation
The Role of Pigmentation
• Skin color is the result of interaction between pigments in epidermis and
blood flow in dermis
– Epidermis contains varying amounts of 2 pigments:
• Carotene: orange-yellow pigment
– Present in orange vegetables (carrots, squashes)
» Eating large amounts of these vegetables can cause lightskinned individuals to appear orange
– Accumulates in epidermal cells and fatty tissues of the dermis
– Can be converted to vitamin A
» Vitamin A is required for normal maintenance of epithelial
tissue and for synthesis of photoreceptor pigments in eyes
• Melanin: yellow-brown or black pigment produced by melanocytes in
stratum germinativum
– Stored in transport vesicles
called melanosomes
– Melanocyte activity
increases in response to
sunlight exposure
– Freckles represent areas of
greater melanin production
Melanin and UV
• Melanin helps prevent skin damage by absorbing UV radiation before
it reaches deep layers of epidermis and dermis
– Ultraviolet (UV) radiation causes DNA mutations and burns that
lead to cancer and wrinkles
• Melanin concentrates around nuclear envelope and absorbs
UV radiation before it can damage nuclear DNA
• Long-term damage can still result from repeated exposure to
sunlight
– Global depletion of ozone in upper atmosphere has caused
a sharp increase in rate of skin cancers like malignant
melanoma
– Skin color depends on melanin
production, not on the number
of melanocytes
• Albinism results from lack of
melanin production by
melanocytes
Skin Color and Dermal Circulation
• Dermal circulation also contributes to skin color
– Oxygenated red blood contributes to skin color:
• Blood vessels in dermis normally give skin a reddish tint that is
most apparent in lightly-pigmented individuals
• Skin reddens even further when blood vessels dilate from heat
• Skin pales if blood flow decreases as a result of temporary
blood vessel constriction
– Cyanosis: bluish skin tint caused by sustained reduction in
circulatory supply
» Apparent in areas of thin skin (lips, ears, beneath nails)
» Can be caused by extreme cold or circulatory (heart
failure) and respiratory (asthma) disorders
5-3 Sunlight has detrimental
and beneficial effects
on the skin
The Epidermis and Vitamin D3
• Limited exposure to sunlight is very beneficial
– In presence of UV radiation, epidermal cells in stratum
spinosum and stratum germinativum convert a cholesterolrelated steroid into vitamin D3
• Liver and kidneys convert vitamin D3 into calcitriol:
– Calcitriol is a hormone that aids absorption of calcium
and phosphorus by small intestine
– Insufficient vitamin D3 can lead to abnormally weak and
flexible bones (rickets)
Types of Skin Cancer
• Interaction between sunlight and skin cells can sometimes result in
different forms of skin cancer
– Some skin cancers rarely metastasize and can usually be
removed surgically:
• Basal cell carcinoma: most common form of skin cancer that
originates in stratum germinativum (basal) layer
• Squamous cell carcinoma: involves more superficial layers of
epidermal cells
– Malignant melanomas are extremely dangerous in comparison
• Usually begin as moles that can appear anywhere on the body
• Cancerous melanocytes then grow rapidly and metastasize
through the lymphoid
system
• Outlook for long-term
survival depends on
when condition is
detected and treated
5-4 The dermis is the
tissue layer that
supports the epidermis
The Dermis
• The Dermis is located between epidermis and subcutaneous layer
– Anchors epidermal accessory structures (hair follicles, sweat
glands):
– Has two major components:
• Outer papillary layer: consists of loose connective (areolar)
tissue that supports and nourishes the epidermis
– Contains capillaries and nerves supplying the skin surface
– Has dermal papillae projecting between epidermal ridges
• Deep reticular layer: consists of interwoven meshwork of
dense irregular connective tissue containing both collagen and
elastic fibers
– Elastic fibers provide flexibility
– Collagen fibers limit flexibility to prevent tissue damage
» Collagen fibers also extend into subcutaneous layer
below
– Contains larger blood vessels, lymph vessels, and nerve
fibers
Other Components of the Dermis
• Dermis also contains mixed cell populations of connective tissue
proper
• Epidermal accessory organs also extend into the dermis
– Include hair follicles and sweat glands
• Other organ systems communicate with skin through their
connections to the dermis
– Both the papillary and reticular layer contain blood vessels
(cardiovascular system), lymphatic vessels (lymphoid system) and
nerve fibers (nervous system)
• Blood vessels provide nutrients and oxygen and remove
carbon dioxide and waste products
• Lymphatic vessels help local
tissues defend and repair
themselves after injury or
infection
• Nerve fibers control blood
flow, adjust gland secretion
rates, and monitor sensory
receptors
5-5 The hypodermis is tissue
that connects the dermis to
underlying tissues
The Hypodermis
• The subcutaneous layer or hypodermis is located below the dermis
– Not actually part of integumentary system
• Important in stabilizing position of skin relative to underlying tissues
while allowing independent movement
• Is connected to the reticular layer of integument by connective tissue
fibers
– Has few capillaries and no vital organs
• Make it useful as the site of subcutaneous injections using
hypodermic needles
– Consists of loose connective (areolar) tissue with many fat cells
• Adipose tissue provides infants with layer of “baby fat” that helps
reduce heat loss
• Fat cells also serves as energy reserve and shock absorber to
support active lifestyles of younger children
• Distribution of subcutaneous fat changes after puberty
– Men accumulate fat at neck, upper arms, along lower back, and
over buttocks
– Women accumulate fat in breasts, buttocks, hips, and thighs
5-6 Hair is composed of
keratinized dead cells that
have been pushed
to the surface
Hair
• Hair, hair follicles, sebaceous glands, sweat glands, and nails
are integumentary accessory structures
– Located in dermis
– Project through skin surface
• Hair: nonliving structure produced in organs called hair follicles
– Project above skin surface almost everywhere on human body
• Exceptions include sides and
soles of feet, palms, sides of
fingers and toes, lips, and
portions of external genital
organs
Hair Follicles and Hairs
• Hair follicles project deep into dermis and often extend into subcutaneous
layer
– Walls of each follicle contain all cell layers found in epidermis
– Base of follicle consists of a peg of connective tissue containing
capillaries and nerves called the hair papilla
• Epithelium at base of follicle forms a cap over this hair papilla
– Hair is formed by repeated division of epithelial stem cells
surrounding the hair papilla
– Hair lengthens as daughter cells are pushed toward the surface
– About halfway to skin surface,
these cell also undergo
keratinization and die
» Marks the boundary between
the hair root (portion that
anchors hair into skin) and
hair shaft (the portion of hair
we see)
Structure of Hair Follicles
• Each hair shaft is made of 3 layers of dead, keratinized
cells
– Cuticle: surface layer made of an overlapping, shinglelike layer of cells
– Cortex: middle layer of hair shaft
• Both the cuticle and cortex contain thick layers of
hard keratin that gives hair its stiffness
– Medulla: deepest layer of hair shaft
making up the core of hair
• Contains a
flexible
soft keratin
The Hair Growth Cycle
• Hairs grow and are shed according to the hair growth cycle
– Hairs in scalp grow for 2-5 years at a rate of ~0.3mm/day
– The follicle of these hairs may then become inactive for a
comparable amount of time
– When another growth cycle begins, the follicle produces a
new hair
• Causes old hair to be pushed to the surface and shed
– Variations in growth rate and length of hair growth cycle
account for differences in uncut hair length among
individuals
• Other differences in hair appearance result from the size
of follicles and shapes of hairs
– Ex) Straight hairs are round when viewed in cross
section while curly ones are rather flat
Functions of Hair
• Functions of Hair
– Hairs on scalp:
• Protect scalp from UV light
• Cushions light blows to head
• Insulate skull
– Hairs guarding orifices (nostrils, ear canals, eyes)
• Help prevent entry of foreign particles
– All hairs are sensitive to very light touch
• Provides an early warning system that may help prevent injury
• Arrector pili muscles extend from papillary
dermis to connective tissue sheath that
surrounds each hair follicle
– These muscles pull of hair follicles when
stimulated, forcing hair to stand up
– Contraction may be caused by
emotional states (fear, rage) or as a
response to cold (“goose bumps”)
Hair Color
• Hair color reflects differences in type and amount of
pigment produced by melanocytes at hair papilla
– Different forms of melanin produce hair colors that
range from black to red
• These pigment difference are genetically determined
– Hormonal and environmental factors also influence hair
• Hair color lightens as pigment production decreases
with age
– White hair results from both lack of pigment and
air bubbles within hair shaft
– Hair color is described as gray as proportion of
white hairs increases
5-7 Sebaceous glands and
sweat glands are
exocrine glands found in the skin
Sebaceous Glands
• Sebaceous Glands (oil Glands): holocrine glands that discharge an oily
lipid secretion into hair follicles or onto skin surface
– Caused by contraction of arrector pili muscle
• Squeezes the gland and forces
the oily secretion into the hair
follicle and onto surrounding
skin
– Secretion is called sebum
• Lubricates hair and skin and inhibits bacterial growth
– Sensitive to changes in concentrations of sex hormones
• Secretions accelerate at puberty, causing individuals with large
glands to be prone to acne during adolescence
– Acne occurs when sebaceous ducts become blocked and
secretions accumulate, causing inflammation and a raised
“pimple”
– Include sebaceous follicles: large sebaceous glands that discharge
sebum directly onto the skin
• Located on face, back, chest, nipples, and external genitalia
Apocrine Sweat Glands
• The skin also contains 2 types of sudoriferous (sweat) glands:
apocrine and merocrine sweat glands
– Apocrine sweat glands: secrete their products into fair follicle in
armpits, around nipples, and in the groin
• Originally thought to use apocrine method of secretion
– We now know that they rely on merocrine secretion
• These glands begin producing sweat at puberty
• Sweat becomes odorous when bacteria break it down
as a food source
– In most mammals, this odor is an
important form of communication
– In humans, this odor is masked by
deodorants and antiperspirants
» Antiperspirants contain astringent
compounds that contract skin and
sweat gland openings, decreasing
the quantity of secretion
Merocrine Sweat Glands
• Merocrine (eccrine) sweat glands: coiled tubular glands that
discharge their secretions directly onto skin surface
– Far more numerous and widely distributed than apocrine
glands
• Ex) Adult skin contains 2-5 millions of these glands
– Palms and soles have the highest numbers of
merocrine glands (500/square centimeter)
– Sweat (perspiration) produced by
merocrine glands is 99% water
• Also contains a mixture of
electrolytes (NaCl), organic
nutrients, and waste products
(urea)
– Sodium chloride gives sweat its
salty taste
Merocrine Sweat Gland Function
• Primary function of merocrine secretions is to cool skin surface
and lower body temperature
– Excessive perspiration, however, can lead to problems
• Perspiration results in excretion of water and electrolytes
from the body
• Perspiration may exceed 1 gallon/hour when all
merocrine sweat glands are working at maximum rate
– Can cause dangerous fluid and electrolyte loss
• Sweat also provides protection from environmental hazards
– Dilutes harmful chemicals in contact with skin
– Flushes microorganisms from skin surface
– Also contains molecule with antibiotic properties called
dermicidin
• Provides additional protection from microorganisms
Modified Sweat Glands
• The skin also contains other types of modified
sweat glands with specialized secretions
– Mammary glands in breasts are similar in structure
to apocrine sweat glands
• These glands secrete milk
– Ceruminous glands in passageway of external ear
have specialized secretions
• Combine with those of nearby sebaceous glands to form
earwax
5-8 Nails are keratinized
epidermal cells that protect
the tips of fingers and toes
Nails
• Nails: form on dorsal surfaces of fingers and toes
– Protect exposed tips and limit distortion when subjected to
mechanical stress
– Nail body is made of dead cells packed with keratin
• Covers a recessed level of epidermis called the nail bed
• Nail production occurs in a deep epidermal fold not visible from the
surface called the nail root
– Portion of the stratum corneum of this
fold extends over exposed nail near
root, forming the cuticle (eponychium)
– Underlying blood vessels give nails
their pink color
• These vessels may be obscured
near the root, leaving a pale
crescent called a lunula
5-9 Several steps are involved
in repairing the integument
following an injury
Repair of Skin Injuries
• Skin can regenerate even after considerable damage
because stem cells are present in both its epithelial and
connective tissue components
– Division of these stem cells produces epidermal and
dermal cells
– Process can be slow and complicated
• Infection and fluid loss can result when large surface
areas are involved
– Relative speed and effectiveness of repair varies
depending on type of wound
• Slender, straight cuts called incisions may heal
relatively quickly
• Scrapes that involve larger areas, known as
abrasions, need more time to heal
Repair of Skin Injuries
• There are 4 stages in the regeneration of skin following an
injury:
– Step 1: Bleeding occurs at site of injury immediately
after being incurred
• Mast cells in this region trigger the inflammatory
response
– Results in enhanced
blood flow to
surrounding regions
and attraction of
phagocytes
Repair of Skin Injuries
• There are 4 stages in the regeneration of skin following an injury:
– Step 2: A blood clot (scab) forms temporarily at the surface to restore
integrity of epidermis and restrict additional entry of microorganisms
• Clot consists mainly of a network of fiber proteins called fibrins that
form from blood proteins during the clotting response
• Cells of stratum germinativum rapidly divide and begin to migrate
along sides of wound to replace missing epidermal cells
• Macrophages and newly-arrived phagocytes patrol damaged area of
dermis and clear away debris and pathogens
• If the wound covers an extensive area or
involves a region of thin skin, dermal repairs
must be underway before epithelial cells can
cover the surface
– Fiber-producing cells (fibroblasts) and
connective tissue stem cells divide to
produce mobile cells that invade deeper
areas of injury
– Epithelial cells lining damaged blood
vessels follow these fibroblasts as they
begin to divide to form capillaries
• Combination of blood clot, fibroblasts, and an extensive capillary
network is called granulation tissue
Repair of Skin Injuries
• There are 4 stages in the regeneration of skin
following an injury:
– Step 3: One week after injury:
• The clot dissolves
• Number of capillaries
declines
• Fibroblast activity has
formed an extensive
meshwork of collagen
fibers in the dermis
Repair of Skin Injuries
• There are 4 stages in the regeneration of skin following an
injury:
– Step 4: After several weeks, the scab is shed and the
epidermis is complete
• These repairs do not restore integument to its original
condition:
– Dermis now contains an abnormally large number of
collagen fibers and relatively
few blood vessels
– Severely damaged hair follicles,
sebaceous and sweat glands,
muscle cells, and nerves are
seldom repaired and instead
replaced by fibrous tissue
» Leads to the formation of an
inflexible, fibrous,
noncellular scar tissue that
will gradually elevate the
overlying epidermis
Scar Formation
• Process of scar formation is highly variable
– Surgical procedures performed on fetuses do not leave
scars
– In some adults, especially those with dark skin, scar
tissue formation may continue beyond requirements of
tissue repair
• Results in a flattened mass of scar tissue called a
keloid
– Begins at injury site and grows into surrounding
dermis
– Covered by shiny, smooth epidermal surface
– Most commonly develop on upper back,
shoulders, anterior chest, and earlobes
Effects of Burns
• Burns are a type of skin injury that can have many causes
– Include exposure of skin to heat, radiation, electrical
shock, or strong chemical agents
• Severity of injury depends on depth of penetration and total
area affected
– Larger affected areas correlate with greater impact on
integumentary function
– The most common classification of burns is based on the
depth of penetration (see below)
5-10 Effects of aging include
dermal thinning, wrinkling, and
reduced melanocyte activity
Effects of Aging
• Aging affects all components of the integument and causes several
major changes:
– Skin injuries and infections become more common
• Due to thinning of epidermis and decline in stem cell activity
– The sensitivity of the immune system is reduced
• Number of macrophages and other immune system cells
residing in the skin decreases by ~50%
– Muscles become weaker, and bone strength decreases
• Related to reduced calcium and phosphate absorption caused
by a 75% decline in vitamin D3 production
– Sensitivity to sun exposure increases
• Less melanin is produced as melanocyte activity declines
– The skin becomes dry and often scaly
• Due to declines in glandular activity, sebum production, and
perspiration
Effects of Aging
• Aging affects all components of the integument and causes
several major changes (continued):
– Hair thins and changes color
• Follicles stop functioning or produce thinner, finer hairs
• These hairs are gray or white due to decreased melanocyte
activity
– Sagging and wrinkling of the skin occur
• Dermis becomes thinner and elastic fiber network decreases
in size
• Effects are most pronounced in areas exposed to sun
– The ability to lose heat decreases
• Blood supply to dermis is reduced
• Sweat glands become less active
– Skin repairs proceed relatively slowly
• Repairs can take twice as long as those of a young adult
• Recurrent infection may occurs because these repairs are
so slow
5-11 The integumentary
system provides protection for
all other body systems
Importance of the Integumentary
System
• Protects and interacts with all organ
systems
• Changes in skin appearance are used to
diagnose disorders in other systems
The Integumentary System
in Perspective
Functional Relationships Between
the Integumentary System and Other Systems
The Skeletal System
• The Skeletal System
 provides structural support
• The Integumentary System
synthesizes vitamin D3, essential
for calcium and phosphorus
absorption (bone maintenance
and growth)
The Muscular System
• The Muscular System’s facial
muscles pull against skin of face,
producing expressions important
in communication
• The Integumentary System
synthesizes vitamin D3 , essential
for normal calcium absorption
(calcium ions play an essential
role in muscle contraction)
The Nervous System
• The Nervous System controls
blood flow and sweat gland
activity for thermoregulation;
stimulates contraction of
arrector pili muscles to elevate
hairs
• The Intergumentary System’s
receptors in dermis and deep
epidermis provide sensations of
touch, pressure, vibration,
temperature, and pain
The Endocrine System
• The Endocrine System includes
the sex hormones that stimulate
sebaceous and apocrine gland
activity, and develop secondary
sexual characteristics; suprarenal
hormones alter blood flow to skin
and mobilize lipids from fat cells
• The Integumentary System
synthesizes vitamin D3, precursor
of calcitriol, a hormone produced
by the kidneys
The Cardiovascular System
• The Cardiovascular System
provides oxygen and nutrients;
delivers hormones and cells of
immune system; carries away
carbon dioxide, waste products,
and toxins; provides heat to
maintain normal skin
temperature
• The Integumentary System’s
mast cells produce localized
changes in blood flow and
capillary permeability
The Lymphatic System
• The Lymphoid System assists
in defending the integument by
providing additional
macrophages and mobilizing
lymphocytes
• The Integumentary System
provides physical barriers that
prevent pathogen entry;
macrophages resist infection;
mast cells trigger inflammation
and initiate the immune reponse
The Respiratory System
• The Respiratory System
provides oxygen and eliminates
carbon dioxide
• The Integumentary System’s
hairs guard entrance to nasal
cavity
The Digestive System
• The Digestive System Provides
nutrients for all cells and lipids
for storage by adipocytes
• The Integumentary System
synthesizes vitamin D3, needed
for absorption of calcium and
phosphorus
The Urinary System
• The Urinary System excretes
waste products, maintains
normal body fluid pH and ion
composition
• The Integumentary System
assists in elimination of water
and solutes; keratinized
epidermis limits fluid loss
through skin
The Reproductive System
• The Reproductive System’s
sex hormones affect hair
distribution, adipose tissue
distribution in subcutaneous
layer, and mammary gland
development
• The Integumentary System
covers external genitalia;
provides sensations that
stimulate sexual behaviors;
mammary gland secretions
provide nourishment for
newborn infant