Integumentary System
BIOL241
INTERCONNECTEDNESS
Outline
• Structure and function of integument
– Epidermis
– Dermis
– Hypodermis
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Skin color
Skin cancer
Accessory structures of Integument
Temperature regulation
Aging
Skin Injury and regeneration
Integumentary System (skin)
Skin (Integument)
• Consists of three major regions
– Epidermis – outermost superficial region
– Dermis – middle region
these two together make up the
cutaneous membrane)
– Subcutaneous region (aka Hypodermis or
(superficial fascia) – deepest region
• Also includes all the accessory structures
found in the skin (hair, glands, etc.)
What are some of the functions
of skin?
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Protection
Excretion (salts, water, wastes)
Maintenance of body temperature
Metabolism (Vitamin D3)
Storage (lipids, blood reserve)
Detection of sensation
• Note: skin keeps water in as well as keeping it
out
Hair shaft
Pore
Dermal papillae
(papillary layer
of dermis)
Epidermis
Meissner's corpuscle
Free nerve ending
Reticular layer of dermis
Sebaceous (oil) gland
Arrector pili muscle
Dermis
Sensory nerve fiber
Eccrine sweat gland
Pacinian corpuscle
Artery
Hypodermis
(superficial
fascia)
Vein
Hair root
Hair follicle
Eccrine sweat
gland
Adipose tissue
Hair follicle receptor
(root hair plexus)
Figure 5.1
Parts of the
Cutaneous Membrane
• Outer epidermis:
– superficial epithelium (epithelial tissues) Composed of
keratinized stratified squamous epithelium, consisting
of four distinct cell types and four or five layers
– Cell types include keratinocytes, melanocytes, Merkel
cells, and Langerhans’ cells
– Outer portion of the skin is exposed to the external
environment and functions in protection
• Inner dermis:
– connective tissues (what are they?)
Epidermis
• Avascular stratified squamous epithelium
• Nutrients and oxygen diffuse from
capillaries in the dermis to lower layers of
epidermis
Cells of the Epidermis
• Keratinocytes – produce the fibrous protein
keratin
• Melanocytes – produce the brown pigment
melanin; cell bodies in upper dermis that have
extensions into the epidermis
• Langerhans’ cells – epidermal macrophages
that help activate the immune system
• Merkel cells – function as touch receptors in
association with sensory nerve endings
Organization of the Epidermis:
Figure 5–2
Layers of the Epidermis
Figure 5.2b
The thick of it
Thin Skin
• Covers most of the
body
• Has 4 layers of
keratinocytes
Thick skin
• Covers the palms of
the hands and soles
of the feet
• Has 5 layers of
keratinocytes
Layers of the epidermis are known as
“strata”
Layers of the Epidermis
Top: Free surface of skin
- stratum corneum
- stratum lucidum
- stratum granulosum
- stratum spinosum
- stratum germinativum
Bottom: Basal lamina
1. Stratum Germinativum (Basale)
• The “germinative layer” (or basal layer):
– Deepest epidermal layer firmly attached to the
basal lamina and dermis via
hemidesmosomes
– Consists of a single row of the youngest
keratinocytes along with projections of
melanocytes
– Cells undergo rapid division,
Structures of
Stratum Germinativum
• Epidermal ridges –
– cause the pattern of your fingerprints;
– created by presence of:
• Dermal papillae (tiny mounds):
– increase the area of basal lamina
– Function?
Fingerprints are epidermal ridges
• Which themselves are negative images of
the dermal papilla
Figure 5–4
2. Stratum Spinosum
• “spiny layer”
• 8-10 cells (keratinocytes) thick
• Immature keratinocyte cells continue to
divide, then shrink until cytoskeletons stick
out (spiny), a system of intermediate
filaments attached to desmosomes
• Melanin granules and Langerhans’ cells
are abundant in this layer
3. Stratum Granulosum
• “grainy layer”
• Consists of 3-5 cell layers of keratinocytes
• Cells stop dividing in this layer, dehydrate
and produce tons of proteins:
– Keratohyaline
– Keratin
4. Stratum Lucidum
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The “clear” layer
Only found in thick skin
Covers granulosum
Consists of a few rows of flat, dead
keratinocytes filled with keratin
• The layer appears, ironically, very thin in
slides
• Probably functions to hold on the thicker
corneum layer above
A note on thick vs. thin skin
• Thick skin has an
extra layer (lucidum)
but that is NOT the
reason that it is thicker
than thin skin.
• The reason is the
other layers are
thicker in thick skin
than in thin skin, esp.
s. corneum
5. Stratum Corneum
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The “horn layer”:
exposed surface of skin
15 to 30 layers of keratinized cells
Accounts for ¾ of epidermal thickness
water resistant (not water proof!)
Protects from abrasion and penetration
shed and replaced every 2 - 4 weeks
Skin is often called a cornified epithelium
Skin Life Cycle
• It takes 15–30 days for a cell to move from
stratum germinosum to stratum corneum
Layers of the Epidermis
Figure 5.2b
Dermis consists of connective tissue
The Dermis
• Deeper part of cutaneous layer
• Located between epidermis and subcutaneous
layer
• Anchors epidermal accessory structures (hair
follicles, sweat glands)
• Contains strong, flexible connective tissue
• Cell types include fibroblasts, macrophages, and
occasionally mast cells and white blood cells
• Has 2 components:
– outer papillary layer
– deep reticular layer
The Papillary Layer
• Consists of areolar tissue with collagen
and elastic fibers
• Contains smaller capillaries, lymphatic
vessels, and sensory neurons
• Has dermal papillae projecting between
epidermal ridges
The Reticular Layer
• Consists of dense irregular connective tissue
• Accounts for approximately 80% of the thickness
of the skin
• Contains larger blood vessels, lymph vessels,
and nerve fibers
• Collagen fibers in this layer add strength and
resiliency to the skin
• Elastin fibers provide stretch-recoil properties
Contains collagen and elastic fibers
The Subcutaneous Layer
• Subcutaneous layer (superficial fascia or
hypodermis):
– loose connective tissue - areolar and adipose
– connected to the reticular layer of dermis by
connective tissue fibers
– stabilizes the skin
– allows separate movement
– Insulates and stores energy
– location of hypodermic injections
Skin Color
• Skin color depends on three pigments:
– Melanin -yellow to reddish-brown to black
pigment, responsible for dark skin colors
• Freckles and pigmented moles – result from local
accumulations of melanin
• Produced by melanocytes just below stratum
germinativum
• Stored in transport vesicles (melanosomes)
• Projections extend up into epidermal layers
• Some transferred to keratinocytes
– Hemoglobin in red blood cells
– Carotene (minor factor)
Melanocytes
Figure 5–5
Function of Melanocytes
• Ultraviolet (UV) radiation:
– causes DNA mutations and burns which lead
to cancer and wrinkles
• Melanin protects skin from sun damage
• Pigment molecules absorb UV and diffuse
it, preventing it from penetrating to the
DNA of cells in the strata germinativum
and spinosum
Melanocytes
• Skin color depends on amount of melanin
production per melanocyte, not number of
melanocytes.
Capillaries and Skin Color
• Oxygenated red blood contributes to skin
color:
– blood vessels dilate from heat, skin reddens
– blood flow decreases, skin pales
– corpses appear pale and lighter because they
lack this coloration
Cyanosis
• Bluish skin tint
• Caused by severe reduction in blood flow
or oxygenation
• The veins appear blue when blood is
deoxygenated but deoxegenated blood is
NOT blue – it is darker red
Illness and Skin Color
• Jaundice:
– buildup of bile produced by liver
– yellow color
• Addison’s disease:
– and other diseases of pituitary gland
– skin darkening
• Vitiglio:
– loss of melanocytes
– localized loss of color
Vitamin D
• The “sunshine vitamin”
• Epidermal cells produce cholecalciferol
(vitamin D3) in the presence of UV
radiation
• Liver and kidneys convert vitamin D into
calcitriol which aids in absorption of
calcium and phosphorus at the intestines
• Insufficient vitamin D:
– can cause rickets
– Symptoms?
Skin Damage
• Sagging and wrinkles (reduced skin
elasticity) are caused by loss (or decresed
production) of collagen and elastin by
fibrolasts, due to:
– dehydration
– age
– hormonal changes
– UV exposure
Skin Cancer
Figure 5–6
Skin Cancer
• The three major types of skin cancer are:
– Basal cell carcinoma (s. germinativum)
– Squamous cell carcinoma (s. spinosum)
– Melanoma
• The vast majority of all skin cancers are of
the first two types (basal and squamous)
• They rarely metastasize and can be taken
care of by excision; thus they are not
included in most cancer statistics
Melanoma
• Cancer of melanocytes is the most
dangerous type of skin cancer because it
is:
– Highly metastatic
– Resistant to chemotherapy
• Kind of ironic because they evolved to
protect basal cells, but basal cell cancer
has a much better prognosis
Skin Cancers
Figure 5.7a–c
Skin color tradeoff?
• Vitamin D is necessary for bone strength, but if
there is not much UV (high latitudes), individuals
with a lot of melanin have trouble getting enough
Vitamin D. But when UV is plentiful, they are
better protected from skin cancer.
• On the other hand, in places with a lot of UV
(low latitudes), people with very little melanin are
at high risk of skin cancer. But they are more
likely to get enough UV from the sun in low UV
regions.
Use Protection!
Accessory Structures of the Integument
• Are of epidermal lineage (cells are modified
epithelial cells)
• “Originate” in the dermis (this is where you look
to find them)
• Extend through the epidermis to skin surface:
– Hair ad follicles
– nails
– multicellular exocrine glands (sebaceous, sweat)
The Hair Follicle
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Is located deep in dermis
Is made of epidermal tissue
Produces nonliving hairs
Is wrapped in a dense connective-tissue
sheath
• Base is surrounded by sensory nerves
Structures of Hair and Follicles
Figure 5–9a
Structures of Hair
• Arrector pili:
– involuntary smooth muscle
– causes hairs to stand up
– produces “goose bumps”
• Sebaceous glands:
– lubricate the hair
– control bacteria
Properties of hair
• As hair is produced, it is keratinized:
– middle medulla contains flexible soft keratin
– outer cortex and cuticle contain stiff hard
keratin
• Hair Color
– Produced by melanocytes at the hair papilla
(base)
– Determined by genes
Sebaceous glands and follicles
(oil glands):
• Holocrine exocrine glands that secrete waxy, oil
secretion called sebum
– Lubricates and protects the hair and skin epidermis
– Inhibits bacterial growth
• Sebaceous glands:
– associated with most hair follicles (on head and body)
• Sebaceous follicles:
– discharge directly onto skin surface
– found on face and trunk only
– when clogged  acne
Sebaceous glands and follicles
Types of Sweat Glands
• Merocrine (eccrine) sweat glands:
– more numerous, widely distributed on body surface,
especially on palms and soles (thick skin)
– Produce thin sweat for evaporative cooling
• Apocrine sweat glands:
– found in armpits, around nipples, and anogential
areas
– produce thick sweat
 Both are actually merocrine
“Apocrine” Sweat Glands
• Merocrine secretions, not apocrine
• Associated with and discharge into hair
follicles in groin, nipples, and axillae
(armpits)
• Become active at puberty
• Produce sticky, cloudy secretions (thick
sweat) that breaks down, feeds bacteria
and causes odor: pungent, not for cooling
Merocrine Sweat Glands
• Also called eccrine glands:
– discharge directly onto skin surface
– produce thin sweat
– contains water, salts, and organic compounds
• Thin sweat functions
– sensible perspiration for evaporative cooling
– excretes water and electrolytes
– flushes microorganisms and harmful
chemicals from skin
Sweat Glands of the Skin
Merocrine
Apocrine
Other Integumentary Glands
Specialized sweat glands:
• Mammary glands:
– produce milk
• Ceruminous glands:
– protect the eardrum
– produce cerumen (earwax)
Control of Glands
• Autonomic nervous system:
– controls sebaceous and apocrine sweat
glands
– works simultaneously over entire body
• Merocrine sweat glands:
– are controlled independently
– sweating occurs locally (e.g. you can sweat
on just one palm)
Temperature Regulation:
Dermal Circulation
Figure 5–8
Dermal circulation
• Arteries
– Cutaneous plexus: a network of arteries along the
bottom of the reticular layer
– Papillary plexus: capillary network from small arteries
in papillary layer
• proximate source of nutrients for epidermal cells
• Cells in the s. corneum are too far away to be nourished
through difusion – that’s why they are dead
• Venous plexus:
– capillary return deep to the papillary plexus
– Bruises usually occur from breakage of these vessels
Temperature Regulation:
Perspiration
• Sensible perspiration:
– Water excreted by merocrine sweat glands
– Cools skin evaporatively
• Insensible perspiration:
– Interstitial fluid lost by evaporation through the
stratum corneum
– Not so important in cooling but a very
important source of water loss
Water Loss Through Skin
• Dehydration results:
– from damage to stratum corneum, e.g., burns
and blisters (insensible perspiration)
– from immersion in hypertonic solution, e.g.,
seawater (osmosis)
Nerves
• Nerve fibers in the skin control:
– blood flow through the dermis
– gland secretions
– sensory receptor (Merkel cells, Meissner’s
corpuscles)
Temperature Regulation:
Homeostasis
• Skin plays a major role in controlling body
temperature (thermoregulation):
• Body temperature regulation is accomplished by
dilation (cooling) and constriction (warming) of
dermal vessels
– Dilation allows skin to act as a radiator, removes heat from
dermal circulation (radiates heat through skin to
environment); constriction helps retain heat
– evaporation of sensible perspiration improves heat
removal by
Dermal circulation is the most important factor in
body cooling. Sweat makes this cooling more
efficient.
Skin: Effects of Aging
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Decreased numbers of immune cells
Decreased vitamin D3 production
Decreased melanocyte activity
Decreased function of hair follicles
Slower repair rate
Reduction of elastic fibers (wrinkles)
Skin becomes dry and itchy
Subcutaneous fat layer diminishes (cold intolerance)
Decreased glandular activity (sweat and oil glands)
Epidermal and dermal thinning
Reduced dermal blood supply
Aging and thermoregulation (or
“why grandma is always cold”)
1. Epidermis thins, subcutaneous fat decreases,
heat escapes more easily
2. Blood supply to dermis is reduced
– Causes skin to become cooler
– Stimulates thermoreceptors in skin which signal
“coldness,” even in a warm environment
However, there is danger of overheating because:
– reduced merocrine sweat gland activity and reduced
dermal circulation both lessen ability to lower body
temperature effectively
Repair of Localized Injuries
to the Skin: Step 1
• Bleeding occurs
• Mast cells trigger
inflammatory
response
Figure 5–13 (Step 1)
Repair of Localized Injuries
to the Skin: Step 2
• A scab stabilizes
and protects the
area
Figure 5–13 (Step 2)
The Inflammatory Response
• Germinative cells migrate around the
wound
• Macrophages clean the area
• Fibroblasts and endothelial cells move in,
producing granulation tissue
Repair of Localized Injuries
to the Skin: Step 3
• Fibroblasts
produce scar
tissue
• Inflammation
decreases, clot
disintegrates
Figure 5–13 (Step 3)
Repair of Localized Injuries
to the Skin: Step 4
• Fibroblasts strengthen
scar tissue
• A raised keloid forms
Figure 5–13 (Step 4)
Summary
• Structure and function of integument
– Epidermis
– Dermis
– Hypodermis
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Skin color
Skin cancer and other diseases
Accessory structures of Integument
Temperature regulation
Aging
Skin Injury and regeneration