Download Integumentary System


The Integument
o 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
1. Cutaneous membrane (skin)
2. Accessory structures
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
Two Components of the Cutaneous Membrane
1.
Outer epidermis
•
2.
Superficial epithelium (epithelial tissues)
Inner dermis
•
Connective tissues
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
Accessory Structures
o Originate in the dermis
o Extend through the epidermis to skin surface
• Hair
• Nails
• Multicellular exocrine glands
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
Connections
o Cardiovascular system
• Blood vessels in the dermis
o Nervous system
• Sensory receptors for pain, touch, and temperature
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
Hypodermis (Superficial Fascia or Subcutaneous Layer)
o Loose connective tissue
o Below the dermis
o Location of hypodermic injections
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Accessory Structures
Cutaneous Membrane
Hair shaft
Epidermis
Pore of sweat
gland duct
Papillary layer
Tactile corpuscle
Dermis
Reticular layer
Sebaceous gland
Arrector pili muscle
Sweat gland duct
Hair follicle
Lamellated corpuscle
Hypodermis
Nerve fibers
Sweat gland
Artery
Vein
Fat
Cutaneous
plexus
Cutaneous Membrane
Epidermis
Papillary layer
Dermis
Reticular layer
Hypodermis
Accessory Structures
Hair shaft
Pore of sweat
gland duct
Tactile corpuscle
Sebaceous gland
Arrector pili muscle
Sweat gland duct
Hair follicle
Lamellated corpuscle
Nerve fibers
Sweat gland
Artery
Vein
Fat
Cutaneous
plexus

Functions of Skin
o Protection of underlying tissues and organs
o Excretion of salts, water, and organic wastes (glands)
o Maintenance of body temperature (insulation and evaporation)
o Production of melanin
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
Functions of Skin
o Production of keratin
o Synthesis of vitamin D3
o Storage of lipids
o Detection of touch, pressure, pain, and temperature
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
The Epidermis
o Is avascular stratified squamous epithelium
• Nutrients and oxygen diffuse from capillaries in the dermis
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Stratum
corneum
Epidermis
Stratum
lucidum
Epidermal
ridge
Basement
membrane
Dermal
papilla
Dermis
Dermis
Thin skin LM  154
Dermal
papilla
Epidermal
ridge
Thick skin
LM  154
Epidermis
Epidermal
ridge
Dermal
papilla
Dermis
The structural relationship and
interface between the epidermis
and underlying dermis. The
proportions of the various layers
differ with the location sampled.

Cells of the Epidermis
o Keratinocytes
• Contain large amounts of keratin
• Are the most abundant cells in the epidermis
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
Thin Skin
o Covers most of the body
o Has four layers of keratinocytes

Thick Skin
o Covers the palms of the hands and soles of the feet
o Has five layers of keratinocytes
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Stratum
corneum
Basement
membrane
Dermis
Thin skin LM  154
A micrograph of
thin skin, which
covers most of
the exposed
body surface.
Stratum
corneum
Stratum
lucidum
Dermal
papilla
Epidermal
ridge
Thick skin
LM  154
A micrograph of thick
skin, which covers
the surface of the
palms and the soles
of the feet.

Structures of the Epidermis
o
The five strata of keratinocytes in thick skin
o
From basal lamina to free surface
1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4. Stratum lucidum
5. Stratum corneum
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Surface
Stratum
corneum
Stratum
lucidum
Stratum
granulosum
Stratum
spinosum
Stratum basale
Basement
membrane
Papillary layer of dermis
Thick skin
Dermis
LM  210

Stratum Basale
o Is attached to basement membrane by hemidesmosomes
o Forms a strong bond between epidermis and dermis
o Forms epidermal ridges (e.g., fingerprints)
o Dermal papillae (tiny mounds)
• Increase the area of basement membrane
• Strengthen attachment between epidermis and dermis
o Has many basal cells or germinative cells
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Pores of sweat
gland ducts
Epidermal
ridge
Thick skin
SEM  25

Specialized Cells of Stratum Basale
o Merkel cells
• Found in hairless skin
• Respond to touch (trigger nervous system)
o Melanocytes
• Contain the pigment melanin
• Scattered throughout stratum basale
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
Stratum Spinosum — the “spiny layer”
o Produced by division of stratum basale
o Eight to ten layers of keratinocytes bound by desmosomes
o Cells shrink until cytoskeletons stick out (spiny)
o Continue to divide, increasing thickness of epithelium
o Contain dendritic (Langerhans) cells, active in immune response
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
Stratum Granulosum — the “grainy layer”
o Stops dividing, starts producing
• Keratin
• A tough, fibrous protein
• Makes up hair and nails
• Keratohyalin
• Dense granules
• Cross-link keratin fibers
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
Cells of Stratum Granulosum
o Produce protein fibers
o Dehydrate and die
o Create tightly interlocked layer of keratin surrounded by keratohyalin
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
Stratum Lucidum — the “clear layer”
• Found only in thick skin
• Covers stratum granulosum
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
Stratum Corneum — the “horn layer”
• Exposed surface of skin
• 15 to 30 layers of keratinized cells (more in the thickest skin)
• Water resistant
• Shed and replaced every 2 weeks
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
Keratinization
o The formation of a layer of dead, protective cells filled with keratin
o Occurs on all exposed skin surfaces except eyes
o Skin life cycle
o It takes 15–30 days for a cell to move from stratum basale to
stratum corneum
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
Perspiration
o Insensible perspiration
• Interstitial fluid lost by evaporation through the stratum corneum
o Sensible perspiration
• Water excreted by sweat glands
• Dehydration results:
• From damage to stratum corneum (e.g., burns and blisters [insensible
perspiration])
• From immersion in hypertonic solution (e.g., seawater [osmosis])
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
Hydration
o Results from immersion in hypotonic solution (e.g., freshwater
[osmosis])
o Causes swelling of epithelial cells and expansion of the skin to
accommodate the extra water, which appears as wrinkly skin
o No one knows why the skin wrinkles
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
Skin Color is Influenced by Two Pigments
1. Carotene
2. Melanin
o
Blood circulation (red blood cells)
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
Carotene
o Orange-yellow pigment
o Found in orange vegetables
o Accumulates in epidermal cells and fatty tissues of the dermis
o Can be converted to vitamin A
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
Melanin
o Yellow-brown or black pigment
o Produced by melanocytes in stratum basale
o Stored in transport vesicles (melanosomes)
o Transferred to keratinocytes
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Melanocytes
in stratum
basale
Melanin
pigment
Basement
membrane
Melanocytes
LM  600
Melanosome
Keratinocyte
Melanin pigment
Melanocyte
Basement
membrane
Basal cell carcinoma
Melanoma

Function of Melanocytes
o Melanin protects skin from sun damage
o Ultraviolet (UV) radiation
• Causes DNA mutations and burns that lead to cancer and wrinkles
o Skin color depends on melanin production, not number of
melanocytes
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
Capillaries and Skin Color
o Oxygenated red blood contributes to skin color
• Blood vessels dilate from heat, skin reddens
• Blood flow decreases, skin pales
o Cyanosis
• Bluish skin tint
• Caused by severe reduction in blood flow or oxygenation
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
Illness and Skin Color
o Jaundice
• Buildup of bile produced by liver
• Yellow color
o Pituitary tumor
• Excess MSH (melanocyte stimulating hormone)
o Addison’s disease
• A disease of the pituitary gland
• Skin darkening
o Vitiligo
• Loss of melanocytes
• Loss of color
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
Vitamin D3
o Epidermal cells produce cholecalciferol (vitamin D3)
• In the presence of UV radiation
o Liver and kidneys convert vitamin D3 into calcitriol
• Aids absorption of calcium and phosphorus
o Insufficient vitamin D3
• Can cause rickets and depressed immune system
• Has been shown as a potential treatment for MS (in conjuction with
traditional treatments)
• Low levels appear in those with some cancers
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
Epidermal Growth Factor (EGF)
o Powerful growth factor
o Produced by glands (salivary and duodenum)
o Used in laboratories to grow skin grafts

Functions of EGF
o Promotes division of germinative cells
o Accelerates keratin production
o Stimulates epidermal repair
o Stimulates glandular secretion
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
The Dermis
o
Located between epidermis and subcutaneous layer
o
Anchors epidermal accessory structures (hair follicles, sweat
glands)
o
Two components
1. Outer papillary layer
2. Deep reticular layer
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
The Papillary Layer
o Consists of areolar tissue
o Contains smaller capillaries, lymphatics, and sensory neurons
o Has dermal papillae projecting between epidermal ridges
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
The Reticular Layer
o Consists of dense irregular connective tissue
o Contains larger blood vessels, lymphatic vessels, and nerve fibers
o Contains collagen and elastic fibers
o Contains connective tissue proper
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
Dermatitis
o An inflammation of the papillary layer
o Caused by infection, radiation, mechanical irritation, or chemicals
(e.g., poison ivy)
o Characterized by itch or pain, redness, and/or flaky skin
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
Dermal Strength and Elasticity
o
Presence of two types of fibers
1. Collagen fibers
• Very strong, resist stretching but bend easily
• Provide flexibility
2. Elastic fibers
• Permit stretching and then recoil to original length
• Limit the flexibility of collagen fibers to prevent damage to
tissue
• Skin turgor
• Properties of flexibility and resilience
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
Skin Damage
o Sagging and wrinkles (reduced skin elasticity) are caused by:
• Dehydration
• Age
• Hormonal changes
• UV exposure
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
Skin Damage
o Stretch marks
• Thickened tissue resulting from excessive stretching of skin due
to:
• Pregnancy
• Weight gain
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
Cleavage Lines
o Collagen and elastic fibers in the dermis
• Arranged in parallel bundles
• Resist force in a specific direction
o Cleavage (tension) lines establish important patterns
• A parallel cut remains shut, heals well
• A cut across (right angle) pulls open and scars
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ANTERIOR POSTERIOR

The Dermal Blood Supply
o Cutaneous plexus
• A network of arteries along the reticular layer
o Papillary plexus
• Capillary network from small arteries in papillary layer
o Venous plexus
• Capillary return deep to the papillary plexus
o Contusion
• Damage to blood vessels resulting in “black-and-blue” bruising
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Dermal
papillae
Epidermal
ridges
Hair
Papillary
layer
Reticular
layer
Cutaneous
plexus
Papillary
plexus
Capillary loop
of papillary
plexus

Innervation of the Skin
o Nerve fibers in skin control:
• Blood flow
• Gland secretions
• Sensory receptors
• Light touch—tactile corpuscles, located in dermal papillae
• Deep pressure and vibration—lamellated corpuscles, in the reticular layer
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
The Hypodermis (Subcutaneous Layer)
o Lies below the integument
o Stabilizes the skin
o Allows separate movement
o Made of elastic areolar and adipose tissues
o Connected to the reticular layer of integument by connective
tissue fibers
o Few capillaries and no vital organs
o The site of subcutaneous injections using hypodermic needles
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
Deposits of Subcutaneous Fat
o Distribution patterns determined by hormones
o Reduced by cosmetic liposuction (lipoplasty)
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
Hair, Hair Follicles, Sebaceous Glands, Sweat Glands, and
Nails
o Integumentary accessory structures
o Derived from embryonic epidermis
o Located in dermis
o Project through the skin surface
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
Human Body
o The human body is covered with hair, except:
• Palms
• Soles
• Lips
• Portions of external genitalia
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
Functions of Hair
o Protects and insulates
o Guards openings against particles and insects
o Is sensitive to very light touch
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
The Hair Follicle
o Located deep in dermis
o Produces nonliving hairs
o Wrapped in a dense connective tissue sheath
o Base is surrounded by sensory nerves (root hair plexus)
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
Accessory Structures of Hair
o Arrector pili
• Involuntary smooth muscle
• Causes hairs to stand up
• Produces “goose bumps”
o Sebaceous glands
• Lubricate the hair
• Control bacteria
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
Regions of the Hair
o Hair root
• Lower part of the hair
• Attached to the integument
o Hair shaft
• Upper part of the hair
• Not attached to the integument
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Exposed
shaft
of hair
Sebaceous
gland
Arrector
pili
muscle
Connective
tissue sheath
Root hair
plexus
Single hair follicle, showing
the associated accessory
structures; a superficial
view of the deeper portions
of the follicle illustrates the
connective tissue sheath
and the root hair plexus.
Hair Structure
The medulla, or
core, of the hair
contains a flexible
soft keratin.
The cortex contains thick
layers of hard keratin,
which give the hair its stiffness.
The cuticle, although
thin, is very tough, and
it contains hard keratin.
Follicle Structure
The internal root sheath surrounds
the hair root and the deeper portion of
the shaft. The cells of this sheath
disintegrate quickly, and this layer does
not extend the entire length of the hair
follicle.
The external root sheath extends
from the skin surface to the hair matrix.
The glassy membrane is a thickened,
clear layer wrapped in the dense
connective tissue sheath of the follicle
as a whole.
Cross section through a
hair follicle and a hair, near
the junction between the
hair root and hair shaft.
Connective tissue sheath
Hair shaft
Boundary
between
hair shaft
and
hair root
Sebaceous
gland
Arrector
pili muscle
Hair root
Connective
tissue sheath
Hair bulb
Hair matrix
Hair papilla
Diagrammatic sectional
view along the long axis
of a hair follicle.
Sebaceous gland
Hair shaft
Hair
Glassy membrane
Subcutaneous adipose
tissue
Connective tissue sheath
of hair
Cortex
Medulla
Hair matrix
Papilla
Hair bulb
Longitudinal section through two
hair follicles, showing the base of
the follicle and the matrix and
papilla at the root of the hair.

Hair Production
o Begins at the base of a hair follicle, deep in the dermis
• The hair papilla contains capillaries and nerves
• The hair bulb produces hair matrix
• A layer of dividing basal cells
• Produces hair structure
• Pushes hair up and out of skin
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
Hair Shaft Structure
o Medulla
• The central core
o Cortex
• The middle layer
o Cuticle
• The surface layer
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
Keratin
o As hair is produced, it is keratinized
• Medulla contains flexible soft keratin
• Cortex and cuticle contain stiff hard keratin
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
Hair Growth Cycle
o Growing hair
• Is firmly attached to matrix
• Club hair
• Is not growing because it is in its final stage of
growth
• Is attached to an inactive follicle
• Once the club hair is gone, no more hair will
emerge from that follicle
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
Hair Growth Cycle
o New hair growth cycle
• Follicle becomes active
• Produces new hair
• Club hair is shed
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
Types of Hairs
o Vellus hairs
• Soft, fine
• Cover body surface
o Terminal hairs
• Heavy, pigmented
• Head, eyebrows, and eyelashes
• Other parts of body after puberty
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
Hair Color
o Produced by melanocytes at the hair papilla
o Determined by genes
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
Exocrine Glands in Skin
o
o
Sebaceous Glands (oil glands)
•
Holocrine glands
•
Secrete sebum
Two Types of Sweat Glands
1. Apocrine glands
2. Merocrine (eccrine) glands
•
Watery secretions
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
Types of Sebaceous (Oil) Glands
o Simple branched alveolar glands
• Associated with hair follicles
o Sebaceous follicles
• Discharge directly onto skin surface
• Sebum
• Contains lipids and other ingredients
• Lubricates and protects the epidermis
• Inhibits bacteria
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Sebaceous follicle
Sebaceous gland
Lumen
(hair removed)
Wall of hair follicle
Epidermis
Dermis
Basement
membrane
Discharge of
sebum
Lumen
Breakdown of
cell membranes
Mitosis and growth
Subcutaneous
layer
Basal cells
Sebaceous gland
LM  150
Sebaceous follicle
Epidermis
Dermis
Subcutaneous
layer
Sebaceous gland
Lumen
(hair removed)
Wall of hair follicle
Basement
membrane
Discharge of
sebum
Lumen
Breakdown of
cell membranes
Mitosis and growth
Basal cells
Lumen
(hair removed)
Wall of hair follicle
Basement
membrane
Basal cells
Sebaceous gland
LM  150

Apocrine Sweat Glands
o Found in armpits, around nipples, and groin
o Secrete products into hair follicles
o Produce sticky, cloudy secretions
o Break down and cause odors
o Surrounded by myoepithelial cells
• Squeeze apocrine gland secretions onto skin surface
• In response to hormonal or nervous signal
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Myoepithelial cell
Sweat pore
Connective
tissue of dermis
Duct
Apocrine
gland cells
Lumen
Duct of
apocrine
sweat gland
Sectional plane
through apocrine
sweat gland
Apocrine sweat gland
LM  459
Apocrine sweat glands
secrete a thick, odorous
fluid into hair follicles.
A section
through a
merocrine
sweat gland

Merocrine (Eccrine) Sweat Glands
o Widely distributed on body surface
o Especially on palms and soles
o Coiled, tubular glands
o Discharge directly onto skin surface
o Sensible perspiration
o Water, salts, and organic compounds
o Functions of merocrine sweat gland activity
• Cools skin
• Excretes water and electrolytes
• Flushes microorganisms and harmful chemicals from skin
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Sweat pore
Duct
Myoepithelial
cells
Merocrine
gland cells
Duct of
apocrine
sweat gland
Lumen
Sectional plane
through apocrine
sweat gland
A section
through a
merocrine
sweat gland
Merocrine
sweat gland
LM  243
Merocrine sweat glands
discharge a watery fluid
onto the surface of the
skin.

Other Integumentary Glands
1.
Mammary glands
• Produce milk
2.
Ceruminous glands
• Produce cerumen (earwax)
• Protect the eardrum
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
Control of Glands
o Autonomic nervous system (ANS)
• Controls sebaceous and apocrine sweat glands
• Works simultaneously over entire body
o Merocrine sweat glands
• Controlled independently
• Sweating occurs locally
o Thermoregulation
• The main function of sensible perspiration
• Works with cardiovascular system
• Regulates body temperature
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
Nails
o Protect fingers and toes
o Made of dead cells packed with keratin
o Metabolic disorders can change nail structure

Nail Production
o Occurs in a deep epidermal fold near the bone called the nail root
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Direction
of growth
Lateral
nail
groove
Free edge
Nail
body
Lateral nail fold
Nail body
Lunula
Proximal
nail fold
Nail
bed
Phalanx
(bone of
fingertip)
Eponychium
A cross-sectional
view
A superficial view
Eponychium
Lunula
Proximal nail fold
Nail body
Nail root
Epidermis
Dermis
A longitudinal section
Phalanx
Hyponychium

Repair of the Integument Following an Injury
o Bleeding occurs
o Mast cells trigger inflammatory response
o A scab stabilizes and protects the area
o Germinative cells migrate around the wound
o Macrophages clean the area
o Fibroblasts and endothelial cells move in, producing granulation
tissue
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Bleeding occurs at the site
of injury immediately after
the injury, and mast cells
in the region trigger an
inflammatory response.
Epidermis
Dermis
Mast cells
After several hours, a
scab has formed and cells
of the stratum basale are
migrating along the edges
of the wound. Phagocytic
cells are removing debris,
and more of these cells
are arriving via the
enhanced circulation in
the area. Clotting around
the edges of the affected
area partially isolates the
region.
Migrating
epithelial
cells
Macrophages
and fibroblasts
Granulation
tissue
One week after the injury,
the scab has been
undermined by epidermal
cells migrating over the
meshwork produced by
fibroblast activity.
Phagocytic activity
around the site has
almost ended, and the
fibrin clot is breaking up.
Fibroblasts
After several weeks, the
scab has been shed, and
the epidermis is complete.
A shallow depression
marks the injury site, but
fibroblasts in the dermis
continue to create scar
tissue that will gradually
elevate the overlying
epidermis.
Scar
tissue

Repair of the Integument Following an Injury
o Fibroblasts produce scar tissue
• Inflammation decreases, clot disintegrates
• Fibroblasts strengthen scar tissue
• A raised keloid may form, which is an overgrowth of collagen during the
healing process
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Head 9%
Upper limb
9% each
Trunk 36%
(front and back)
Head 15%
Trunk 32%
(front and back)
Genitalia 1%
Upper limb 9% each
Lower limb
18% each
Genitalia 1%
Lower limb
17% each
ADULT
CHILD (5-year-old)

Effects of Aging
o Epidermal thinning
o Decreased numbers of dendritic (Langerhans) cells
o Decreased vitamin D3 production
o Decreased melanocyte activity
o Decreased glandular activity (sweat and oil glands)
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
Effects of Aging
o Reduced blood supply
o Decreased function of hair follicles
o Reduction of elastic fibers
o Decreased hormone levels
o Slower repair rate
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
Importance of the Integumentary System
o Protects and interacts with all organ systems
o Changes in skin appearance are used to diagnose disorders in other
systems
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