Integumentary System
Skin, Hair, Nails, Associated Glands & Structures
Skin is sometimes called the cutaneous membrane.
Skin & Accessory Structures
• Skin
– large waterproof covering
– UV light and chemical protection
– Covers 3000 square inches of the body
– Weighs 6 lbs
– Helps regulate body temperature
• Accessory structures
– hair, nails, glands
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Skin Functions
• Protects deeper tissues from:
– Mechanical damage
– Chemical damage
– Bacterial damage
– Thermal damage
– Ultraviolet radiation
– Desiccation
Skin Functions
• Aids in heat regulation
• Aids in excretion of urea and uric acid
• Synthesizes vitamin D
Meissner’s Corpuscle
A Mechanoreceptor of Touch
5.
Epidermis
General Characteristics
• Stratified, squamous, keratinized,
epithelium
• Held together by desmosomes (allows
the flexibility of the skin)
• Thickest on the palm and soles
• Thinnest over the ventral surface of
trunk
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Skin Structure
• Epidermis – outer layer
– Stratified squamous
epithelium
– Often keratinized
(hardened by keratin)
• Dermis
Figure 4.3
Layer of Epidermis
• Stratum corneum
– Shingle-like dead cells
• Stratum lucidum
– Occurs only in thick skin
Layer of Epidermis
• Stratum granulosum
• Stratum spinosum
• Stratum basale
– Cells undergoing mitosis
– Lies next to dermis
The Stratum Corneum
• Outermost layer
• Dead, keratinized cells
• Barrier to light, heat, chemicals,
microorganisms
• “leathery” layer
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Stratum Corneum
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Consists of about 20% water
Constantly losing this layer
Thickness depends on use (hands, soles)
A thick Callus can form from heavy use
Abrasions on the foot produce Corns
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The Stratum Lucidum
• One to two cell layers thick
• Flat and transparent
• Difficult to see
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The Stratum Spinosum
• Several layers of spiny-shaped cells
• Desmosomes prevalent
– Desmosomes: interlocking cellular bridges
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The Stratum Granulosum
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•
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•
•
Two or three layers
Flattened cells
Active keratinization
Lose nuclei
Compact and brittle
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The Stratum Germinativum
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Deepest and most important layer
Rests on basement membrane
Lowermost layer called stratum basale
New cells produced here (mitosis)
This layer must remain intact so the
epidermis will regenerate
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Stratum Germinativum
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•
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Melanocytes - produce melanin
Produces skin color
Irregularly shaped
All races have the same number of
melanocytes, but specific genes that
determine the amount of melanin
produced
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Skin Structure
Figure 4.4
• Non-vascularized
• The lowermost cells divide by mitosis
• Keratinization occurs as new cells rise
– cells move to surface, lose water and nuclei
change
– Filled with keratin (protein)
• Composed of five layers
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The Dermis
True Skin
(Corium)
Divisions of the Dermis
• Papillary
– adjacent to the epidermis
• Reticular
– between papillary and subcutaneous
• Subcutaneous (hypodermis)
– layers of fat below the dermis
– Where you get hypodermic injections
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• Two layers
– Papillary layer
Dermis
• Projections called dermal papillae
• Pain receptors
• Capillary loops
– Reticular layer
• Blood vessels
• Glands
• Nerve receptors
Hypodermis
aka
Subcutaneous Layer
• Deep to dermis
– Not part of the skin
– Anchors skin to underlying organs
– Composed mostly of adipose tissue
Structures Found in Dermis
• The following are all found here in the
dermis
– Blood and lymph vessels
– Nerves
– Muscles
– Glands
– Hair follicles
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Sebaceous Glands
– Produce oil (Sebum)
• Lubricant for skin
• Kills bacteria
– Most with ducts that empty into hair
follicles
Sebaceous Glands
– Brushing hair brings more out
– secretion controlled by endocrine system
– Increases at puberty
• Causes acne
• Later on, it decreases and causes dry skin
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Suderiferous Glands
• Sweat glands
– Widely distributed in skin
– Two types
• Eccrine
– Open via duct to pore on skin surface
• Apocrine
– Ducts empty into hair follicles
Suderiferous Glands
• Sweat
– most numerous in palms and soles
• 3000 per square inch on palms
– Not found on lips or male genitalia
– sweating helps cool the body
• Same materials as blood
• Odorless (smell is bacteria)
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Sweat and Its Function
• Composition
– Mostly water
– Some metabolic waste
– Fatty acids and proteins (apocrine only)
• Function
– Helps dissipate excess heat
– Excretes waste products
– Acidic nature inhibits bacteria growth
• Odor is from associated bacteria
Normal Skin Color Determinants
• Melanin
– Yellow, brown or black pigments
• Carotene
– Orange-yellow pigment from some vegetables
• Hemoglobin
– Red coloring from blood cells in dermis capillaries
– Oxygen content determines the extent of red
coloring
Melanin
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Pigment (melanin) produced by melanocytes
Color is yellow to brown to black
Melanocytes are mostly in the stratum basale
Amount of melanin produced depends upon
genetics and exposure to sunlight
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Dermis
• Pink tint of light skinned individuals is a
result of the blood vessels here
• When you get embarrassed, blood vessels
here dilate and causes blushing
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•Hair
Hair
• One main characteristic of mammals
• Covers most of the surface of the body
• Three parts - cuticle, cortex, medulla
– Cuticle
• Outermost part
– Cortex
• Principal portion of hair
• Contain fibers that determine hair color
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– Medulla
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– central part of the hair
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• Shaft - visible portion
• Root - hair follicle
– Has an outer connective tissue sheath
• Arrector pili - smooth muscle
– Causes goose bumps
– Involuntary
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Hair Characteristics
• Growth
– hair follicle
– cycles of growth and rest
– Begins in the hair bulb (blood vessels to nourish)
– Hair loss occurs because new hair pushes old hair
down – baldness occurs because the follicle is lost too
– The cycles depend on hair:
• Scalp hair grows for 3 years and rests for 1 or 2
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Hair
• Texture - straight, curly, or tightly curly
– Based on keratin in hair
• Color - based on complex genetic factors
– Gray hair occurs due to a loss of pigment in
the cortex
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• Hair
Appendages of the Skin
– Produced by hair
bulb
– Consists of hard
keratinized
epithelial cells
– Melanocytes
provide pigment
for hair color
Figure 4.7c
Hair Anatomy
• Central medulla
• Cortex surrounds
medulla
• Cuticle on outside of
cortex
– Most heavily keratinized
Figure 4.7b
Nails
Nails
• Modified epidermal cells
– Composed of very hard keratin
• Lunula - white crescent
– Caused by air mixed in the keratin
• Body - visible portion
• Root - covered by skin
• Growth occurs from the nailbed
– Grows about 1mm per week
– Cuticle extends over the proximal end of the nail body
– by
Fingernails
grow faster than toe nails
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Nails
– Scale-like modifications of the epidermis
• Heavily keratinized
– Stratum basale extends beneath the nail bed
• Responsible for growth
– Lack of pigment makes them colorless
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•
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Free edge
Body
Root of nail
Eponychium –
proximal nail
fold that
projects onto
the nail body
Figure 4.9
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Miscellaneous
and
Pathology
Homeostatic Imbalances
• Burns
– Tissue damage and cell death caused by heat,
electricity, UV radiation, or chemicals
– Associated dangers
• Dehydration
• Electrolyte imbalance
• Circulatory shock
Rule of Nines
• Way to determine
the extent of burns
• Body is divided into
11 areas for quick
estimation
– Each area represents
about 9%
Figure 4.11a
Severity of Burns
• First-degree burns
– Only epidermis is damaged
– Skin is red and swollen
• Second degree burns
– Epidermis and upper dermis are damaged
– Skin is red with blisters
• Third-degree burns
– Destroys entire skin layer
– Burn is gray-white or black
Critical Burns
• Burns are considered critical if:
– Over 25% of body has second degree burns
– Over 10% of the body has third degree burns
– There are third degree burns of the face, hands, or
feet
Skin Cancer
• Cancer – abnormal cell mass
• Two types
– Benign
• Does not spread (encapsulated)
– Malignant
• Metastasized (moves) to other parts of the body
• Skin cancer is the most common type of
cancer
Skin Cancer Types
• Basal cell carcinoma
– Least malignant
– Most common type
– Arises from statum basale
• Squamous cell carcinoma
– Arises from stratum spinosum
– Metastasizes to lymph nodes
– Early removal allows a good chance of cure
Skin Cancer Types
• Malignant melanoma
– Most deadly of skin cancers
– Cancer of melanocytes
– Metastasizes rapidly to lymph and blood vessels
– Detection uses ABCD rule
ABCD Rule
• A = Asymmetry
– Two sides of pigmented mole do not match
• B = Border irregularity
– Borders of mole are not smooth
• C = Color
– Different colors in pigmented area
• D = Diameter
– Spot is larger then 6 mm in diameter