5
The Integumentary System
Skin (Integument)
Consists of three major regions

1.
2.
3.
Epidermis—superficial region
Dermis—middle region
Hypodermis (superficial fascia)—
deepest region


Subcutaneous layer deep to skin
(not technically part of skin)
Mostly adipose tissue
Hair shaft
Epidermis
Papillary
layer
Dermis
Reticular
layer
Hypodermis
(superficial fascia)
Nervous structures
• Sensory nerve fiber
• Pacinian corpuscle
• Hair follicle receptor
(root hair plexus)
Dermal papillae
Subpapillary
vascular plexus
Pore
Appendages
of skin
• Eccrine sweat
gland
• Arrector pili
muscle
• Sebaceous
(oil) gland
• Hair follicle
• Hair root
Cutaneous vascular
plexus
Adipose tissue
Figure 5.1
Epidermis


The Epidermis is a keratinized stratified squamous
epithelium
Cells of epidermis
 Keratinocytes- produce fibrous protein: keratin
 Keratin helps give skin its protective properties
 Melanocytes
 Found in the deepest layer of the epidermis
 Produce pigment melanin
 Epidermal dendritic (Langerhans) cells- ingest foreign
substances and are key activators of our immune system
 arise from bone marrow

Tactile (Merkel) cells- sensory receptors for touch.
(a)
Dermis
Stratum corneum
Most superficial layer; 20–30 layers of dead
cells represented only by flat membranous
sacs filled with keratin. Glycolipids in
extracellular space.
Stratum granulosum
Three to five layers of flattened cells,
organelles deteriorating; cytoplasm full of
lamellated granules (release lipids) and
keratohyaline granules.
Stratum spinosum
Several layers of keratinocytes unified by
desmosomes. Cells contain thick bundles of
intermediate filaments made of pre-keratin.
Stratum basale
Deepest epidermal layer; one row of actively
mitotic stem cells; some newly formed cells
become part of the more superficial layers.
See occasional melanocytes and epidermal
dendritic cells.
Figure 5.2a
Layers of the Epidermis:
Stratum Basale (Basal Layer)



Deepest epidermal layer firmly
attached to the dermis
 looks like corrugated cardboard
Single row of stem cells
 a continually renewing cell
population
 also called stratum germinativum
because these cells undergo rapid
division
Journey from basal layer to surface of
the skin
 Takes 25–45 days
Layers of the Epidermis:
Stratum Spinosum (Prickly Layer)




Several cell layers thick
Cells contain a weblike system of
intermediate tension resisting
prekeratin filaments attached to
desmosomes (cell structures
specialized for cell to cell adhesion)
Keratinocytes in this layer are
spiked hence the name prickly layer
Abundant melanin granules (skin
color) and dendritic cells (sensory)
Layers of the Epidermis:
Stratum Granulosum (Granular Layer)



Thin; three to five cell layers in
which the cells flatten
Keratinization begins here-cells
fill with protein- keratin)
Keratohyaline (help to form
keratin in the upper layers) and
lamellated granules (contain a
water resistant glycolypid- slow
water loss in the epidermis)
accumulate
Layers of the Epidermis:
Stratum Lucidum (Clear Layer)



In thick skin
Thin, transparent band
superficial to the stratum
granulosum
A few rows of flat, dead
keratinocytes with indistinct
boundaries
Layers of the Epidermis:
Stratum Corneum (Horny Layer)




20–30 rows of dead, flat, keratinized
membranous sacs
Three-quarters of the epidermal thickness
Functions
 Protects from abrasion and penetration
 Waterproofs
 Barrier against biological, chemical,
and physical assaults
This is layer is what makes up your
dander (dry skin) and dandruff (scalp).
 The average person sheds 40 lbs of
skin flakes in a lifetime!
Stratum corneum
Most superficial layer; 20–30 layers of dead
cells represented only by flat membranous
sacs filled with keratin. Glycolipids in
extracellular space.
Stratum granulosum
Three to five layers of flattened cells,
organelles deteriorating; cytoplasm full of
lamellated granules (release lipids) and
keratohyaline granules.
Stratum spinosum
Several layers of keratinocytes unified by
desmosomes. Cells contain thick bundles of
intermediate filaments made of pre-keratin.
Stratum basale
Deepest epidermal layer; one row of actively
mitotic stem cells; some newly formed cells
become part of the more superficial layers. See
occasional melanocytes and epidermal
dendritic cells.
Desmosomes
Melanin granule
Melanocyte
(b)
Keratinocytes
Dermis
Sensory
nerve ending Epidermal
Tactile
dendritic cell
(Merkel) cell
Figure 5.2b
Dermis




This is your hide- corresponds
directly to animal hide that
makes leather.
Strong, flexible connective tissue
Cells include fibroblasts,
macrophages, and occasionally
mast cells and white blood cells
Two layers:
 Papillary
 Reticular
Hair shaft
Epidermis
Papillary
layer
Dermis
Reticular
layer
Hypodermis
(superficial fascia)
Nervous structures
• Sensory nerve fiber
• Pacinian corpuscle
• Hair follicle receptor
(root hair plexus)
Dermal papillae
Subpapillary
vascular plexus
Pore
Appendages
of skin
• Eccrine sweat
gland
• Arrector pili
muscle
• Sebaceous
(oil) gland
• Hair follicle
• Hair root
Cutaneous vascular
plexus
Adipose tissue
Figure 5.1
Layers of the Dermis: Papillary Layer

Papillary layer
 Areolar connective tissue with
collagen and elastic fibers and
blood vessels
 The looseness of this tissue allows
phagocytes and other defensive
cells to wander freely as they
patrol the area for bacteria that
may have breached the skin.

Dermal papillae contain:
 Capillary loops- carry blood to the dermal papillae (extensions
of the dermis into the epidermis)
 Meissner’s corpuscles- touch receptors
 Free nerve endings- pain receptors
Layers of the Dermis: Reticular Layer

Reticular layer
 ~80%
of the thickness of
dermis
 Coarse irregularly
arranged dense fibrous
connective tissue
 Collagen fibers provide
strength and resiliency
 Elastic fibers provide
stretch-recoil properties
Skin Markings: Friction Ridges

Epidermal ridges lie
atop deeper dermal
papillary ridges to
form friction ridges
of fingerprints
Friction ridges
Openings of
sweat gland ducts
(a)
Skin Markings: Cleavage Lines

Collagen fibers arranged in
bundles form cleavage
(tension) lines
 Externally invisible
 Form separations or less
dense regions
 Incisions made parallel to
cleavage lines heal more
readily
Skin Color

Three pigments contribute to
skin color:
1. Melanin
Yellow to reddish-brown to
black, responsible for dark
skin colors



Produced in melanocytes
Freckles and pigmented
moles

Local accumulations of
melanin
Skin Color
2.
Carotene

3.
Yellow to orange, most
obvious in the palms and
soles
Hemoglobin

Responsible for the pinkish
hue of skin
Homeostatic Imbalance

Melanin protects your skin
from sun damage but
excessive sun causes clumping
of elastic fibers which results in
leathery skin; temporarily
depresses the immune system;
and can alter DNA of skin cells
and lead to skin cancer.
Homeostatic Imbalance

Many alterations to skin color signal
certain disease states and in many
people emotional states:
 Redness or erythema: blushing, fever,
hypertension, inflammation, or
allergy
 Pallor or blanching: fear, anger, or
other types of emotional stress cause
a person to become pale. Pale skin
may also indicate anemia or low
blood pressure.
Homeostatic Imbalance
Jaundice or yellow cast: usually signifies
a liver disorder- yellow bile pigments
accumulate in the blood and are
deposited in body tissues.
 Bronzing: A bronze almost metallic
pigment to the skin is a sign of Addison’s
disease in which the adrenal cortex is
producing inadequate amounts of its
steroid hormones. It can also be a sign
of a pituitary tumor.
 Black and blue marks or bruises: reveal
where blood escaped from the
circulation and clotted beneath the skinhematoma.

Appendages of the Skin

Derivatives of the epidermis
 Sweat
glands
 Oil glands
 Hairs and hair follicles
 Nails
Sweat Glands

Two main types of sweat (sudoriferous)
glands
1.
Eccrine (merocrine) sweat glands—
abundant on palms, soles, and
forehead



Sweat: 99% water, NaCl, vitamin C,
antibodies, dermcidin, metabolic
wastes
 Sweat is acidic: pH of 4-6
Simple coiled tubular gland- secretory
part lies coiled in the dermis and the
duct extends to open in funnel shaped
pore at the skin surface.
Function in thermoregulation- prevent
overheating of the body.
Sweat pore
Eccrine
gland
Sebaceous
gland
Duct
Dermal connective
tissue
Secretory cells
(b) Photomicrograph of a
sectioned eccrine gland (220x)
Figure 5.5b
Sweat Glands
2.
Apocrine sweat glands—confined
to axillary and anogenital areas
 Approx. 2000
 Larger the eccrine glands, tend
to lie deeper in the dermis, and
ducts empty into hair follicles
 Secrete sweat + fatty
substances and proteins



Milky or yellowish color
Normally odorless until
bacteria on the skin
decompose organic molecule =
source of body odor
Functional from puberty onward
(as sexual scent glands?)
Sweat Glands

Specialized apocrine glands
 Ceruminous
glands
 Lining
of the external ear canal
 Produce a sticky bitter substance
called cerumen or earwax

To deter insects and block entry of
foreign material
 Mammary
 Secrete
glands
milk
Sebaceous (Oil) Glands




Widely distributed
Most develop from hair follicles
Become active at puberty
Sebum
 Oily
holocrine secretion
 Bactericidal
 Softens hair and skin
Dermal
connective
tissue
Sebaceous
gland
Sebaceous
gland duct
Hair in
hair follicle
Secretory cells
(a) Photomicrograph of a sectioned
sebaceous gland (220x)
Sweat
pore
Eccrine
gland
Figure 5.5a
Homeostatic Imbalance

If a sebaceous gland is blocked by
accumulated sebum a whitehead
appears on the skin.



If the material oxidizes and dries it
darkens to form a blackhead.
Acne is an active inflammation of the
sebaceous glands and is usually
caused by bacterial infection.
Seborrhea known as cradle cap in
infants is caused by overactive
sebaceous glands- it begins on the
scalp as pink raised lesions that
gradually become yellow to brown
and begin to slough off as oily
scales.
Hair

Functions
 Alerting
the body to presence of
insects on the skin
 Guarding the scalp against
physical trauma, heat loss, and
sunlight

Distribution
 Entire
surface except palms, soles,
lips, nipples, and portions of
external genitalia
Hair



Flexible strands consist of dead keratinized cells
Contains hard keratin; tougher, more durable than soft
keratin of skin & individual cells do not flake off.
Hair pigments: melanins (yellow, rust brown, black)
combine to produce hair color from blonde to black
 Red haired is colored by the iron containing
pigment trichosiderin
 Gray/white hair: results from decreased melanin
production, replacement of melanin by air bubbles
in the hair shaft
Follicle wall
Hair shaft
Arrector
pili
Sebaceous
gland
Hair root
• Connective tissue
root sheath
• Glassy membrane
• External epithelial
root sheath
• Internal epithelial
root sheath
Hair
• Cuticle
• Cortex
• Medulla
(a) Diagram of a cross section of
a hair within its follicle
Hair bulb
Figure 5.6a
Hair Follicle



Fold down from the
epidermal surface into
dermis
Two-layered wall: outer
connective tissue root sheath
(derived from the dermis),
inner epithelial root sheath
(derived from the epidermis)
Hair bulb: expanded deep
end 4mm below the skin
surface
Hair Follicle


Hair follicle receptor (root hair plexus)
 Sensory nerve endings around each hair bulb
 Stimulated by bending a hair
 Feel the tickle as you run your hand over
the hairs on your forearm
Arrector pili
 Smooth muscle attached to follicle
 Responsible for “goose bumps”
 Not useful to humans
 Animals use it to stay warm by trapping a layer
of insulating air in between their fur and also to
scare off enemies
Hair shaft
Arrector
pili
Sebaceous
gland
Hair root
Hair bulb
Follicle wall
• Connective tissue root sheath
• Glassy membrane
• External epithelial root sheath
• Internal epithelial root sheath
Hair root
• Cuticle
• Cortex
• Medulla
Hair matrix
Hair papilla
Melanocyte
Subcutaneous adipose tissue
(c) Diagram of a longitudinal view of the expanded hair
bulb of the follicle, which encloses the matrix
Figure 5.6c
Types of Hair


Vellus—pale, fine
body hair of children
and adult females
Terminal—coarse,
long hair of
eyebrows, scalp,
axillary, and pubic
regions (and face
and neck of males)
Types of Hair

Hair Growth
 Growth
and density are
influenced by many factors:

Nutrition


Hormones

 The
Poor nutrition means poor
hair growth
May enhance hair growth
rate of hair growth
varies with sex and age
but averages around 2.5
mm a week
Homeostatic Imbalance


Hirsutism or excessive hairiness
in women
Results from an adrenal gland
or ovarian tumor that secretes
large amounts of androgens
Hair Thinning and Baldness


Alopecia—hair thinning in both sexes after age
40
 Coarse terminal hairs get replaced by vellus
and hair becomes very wispy
True (frank) baldness
 Genetically determined and sex-influenced
condition


Recessive: on the X chromosome- female would
need 2 defective X
Male pattern baldness is caused by follicular
response to DHT- a metabolic testosterone

Growth cycles become short and many hairs
don’t even emerge from their follicles
Structure of a Nail

Scalelike modification of the epidermis on the
distal, dorsal surface of fingers and toes
Functions of the Integumentary System
1.
Protection—three types of barriers
 Chemical
 Low pH secretions (acid mantle) and
defensins (natural antibiotics
secreted by skin) delay bacterial
activity
 Physical/mechanical barriers
 Keratin and glycolipids block most
water and water- soluble substances
 Limited penetration of skin by lipidsoluble substances, plant oleoresins
(e.g., poison ivy), organic solvents,
salts of heavy metals, some drugs
Functions of the Integumentary System
 Biological
barriers
cells -1st line of defense: activators
 Macrophages -2nd – dispose of viruses and bacteria that
have penetrated the epidermis
 DNA- biological sunscreen- converts potentially destructive
radiation into harmless heat.
 Dendritic
Functions of the Integumentary System
Body temperature regulation
2.


Sweat glands secrete about 500 ml/day of
insensible (routine & unnoticeable) perspiration
(at normal body temperature)
At elevated temperature, dilation of dermal
vessels and increased sweat gland activity
(sensible perspirations) cool the body

On a hot day you can lose 12L or 3 gallons of body
water
Cutaneous sensations
3.

Cutenous receptors are classified as
exteroceptors b/c they respond to stimuli
arising outside the body.

Temperature, touch, and pain
Functions of the Integumentary System
Metabolic functions
4.

The skin is a chemical factory fueled in part by the
sun’s rays when sunlight hits the skin, modified
cholesterol molecules are converted to a vitamin D
precursor


Important for calcium metabolism- calcium is not absorbed in
the digestive tract without vitamin D
Skin cells also make collagenase- an enzyme that
aids the natural turnover of collagen and deters
wrinkles.
Functions of the Integumentary System
Blood reservoir—up to 5% of
body’s entire blood volume
5.
•
6.
When other body organs- such as
vigorously working muscles need a
greater blood supply – the nervous
system constricts the blood supply in
the dermal blood vessels, this pushes
more blood into the general
circulation making it available for
other organs.
Excretion—nitrogenous wastes
and salt in sweat
Skin Cancer


1 in 5 Americans develops skin cancer at some point.
 Most skin tumors are benign and do not metastasize (spread )
 Some are malignant or cancerous and invade other body areas
Risk factors
 Overexposure to UV radiation


Frequent irritation of the skin


Damages DNA bases and causes them to fuse.
Infection, chemicals, or physical trauma
There is no healthy tan but some skin lotions contain tiny oily vesicles
called liposomes filled with enzymes that can fix damaged DNA
before the involved cells can develop in to cancer cells.
Skin Cancer

Three major types:
 Basal cell carcinoma
 Least
malignant, most common
 Relatively slow growing and mestasis
seldom occurs before its noticed
 Stratum basale cells proliferate and
invade the dermis and hypodermis
 Accounts for 80% of skin cancers
Skin Cancer
 Squamous
cell carcinoma
Second most common
Arises from the keratinocytes of the stratum
spinosum
Tends to grow rapidly and metastasizes if
not removed
Skin Cancer
Melanoma






Most dangerous
Cancer of melanocytes
Highly metastatic and resistant
to chemotherapy
Accounts only for 2-3% of skin
cancers
Most appear spontaneously but
one third develops from preexisting moles and spreads to
surrounding lymph and blood
vessels
Skin Cancer
 Examine
your skin ABCD ruleAmerican Cancer Society:
Asymmetry: two sides of the
pigmented spot or mole do not
match
B. Border irregularity: border of lesions
exhibit indentations
C. Color: Pigmented spot contains
several colors (blacks, browns, tans,
and sometimes blues and reds)
D. Diameter: The spot is larger than
6mm in diameter (the size of a
pencil eraser)
A.
Burns
Heat, electricity, radiation,
certain chemicals

Burn
(tissue damage, denatured
protein, cell death)
 Immediate threat:

 Dehydration
and electrolyte
imbalance, leading to renal
shutdown and circulatory
shock
Rule of Nines


Used to estimate the
severity and extent of
burns by measuring volume
of fluid loss from burns
Divides the body into 11
areas each accounting for
9% of the total body area
plus an additional area
surrounding the genitals
that accounts for 1% of
body surface area
Partial-Thickness Burns


Burns are classified by
their depth:
First degree
 Epidermal
1st degree
burn
damage only
 Localized
redness, edema
(swelling), and pain

Second degree
 Epidermal
and upper
dermal damage
 Blisters
appear
2nd degree
burn
(a) Skin bearing partial
thickness burn (1st and
2nd degree burns)
Full-Thickness Burns

Third degree
 Entire
thickness of skin
damaged
 Gray-white,
3rd
degree
burn
cherry red,
or black
 No initial edema or pain
(nerve endings
destroyed)
 Skin grafting usually
necessary
(b) Skin bearing full
thickness burn
(3rd degree burn)
Severity of Burns

Critical if:
 >25%
of the body has second-degree burns
 >10% of the body has third-degree burns
 Face, hands, or feet bear third-degree burns
Developmental Aspects: Fetal





Ectoderm  epidermis
Mesoderm  dermis and hypodermis
By the 4th month the skin is fairly well
developed
Lanugo coat: downy covering of
delicate hairs in 5th and 6th month
Vernix caseosa (varnish of cheese):
when a baby is born its covered by a
white cheesy looking substance
produced by the sebaceous gland;
protects skin of fetus within the water
filled amnion
Developmental Aspects: Adolescent to
Adult



Sebaceous gland activity
increases- skin becomes oilier
Skin reaches its optimal
appearance in 20s-30s
Effects of cumulative
environmental assaults show
after age 30
 Abrasion,

wind, sun, chemicals
Scaling and dermatitis become
more common
Developmental Aspects: Old Age




Epidermal replacement slows, skin
becomes thin, dry, and itchy
All of the lubricating substances
produced by the skin glands that
make skin supple and soft become
deficient
Subcutaneous fat and elasticity
decrease, leading to cold
intolerance and wrinkles
Increased risk of cancer due to
decreased numbers of melanocytes
and dendritic cells