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Chapter 5
Integumentary
System
Shaft of a hair protruding through the skin
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Integumentary System
• skin, hair, glands, nails
• Functions
1. Protection
– Against abrasion and UV light
– Prevents entry of microorganisms
– Prevents dehydration
2. Sensation
– Sensory receptors detect heat, cold, touch, pressure, pain
3. Temperature regulation by controlling
– Blood flow through skin
– Sweat gland activity
4. Vitamin D production
5. Excretion of small amounts of waste products
Skin
• SA – 1.2-2.2 m2 and weighs 4-5 kg (9-11 lbs)!!
• 3 major regions
– Epidermis: outermost region (superficial)
• Resists abrasion
• Reduces water loss
– Dermis: middle region (bulk of skin)
• Responsible for most structural strength of skin
• Leather produced from dermis of animals…ewww.
– Subcutaneous tissue (hypodermis): deepest region
• Not really part of skin
• Connects skin to underlying muscle or bone
Fig. 5.1
Tab. 5.1
Epidermis
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keratinized stratified squamous epithelium
4 distinct cell types
4-5 layers
Outer portion exposed to external
environment
– protection
4 Cell Types of Epidermis
• Keratinocytes
– Most abundant
– Produce fibrous protein keratin
– Gives skin its protective properties
• Melanocytes
– Produce brown pigment melanin
– Found in deepest layers of epidermis
• Langerhans’ cells
– Epidermal macrophages
– Help activate immune system
• Merkel cells
– Touch receptors in association with sensory nerve endings
Layers of Epidermis
• Stratum Basale (Basal Layer)
– Deepest, firmly attached to dermis
• Structural strength provided by desmosomes and
hemidesmosomes
– single row of youngest keratinocytes
– Cells undergo mitotic divisions ~every 19 days
– 10-25% are melanocytes
Layers of the Epidermis
• Stratum Spinosum
– Melanin granules and Langerhans’ cells abundant
• Melanin taken up by keratinocytes, accumulates on “sunny side”
to protect nucleus from UV damage
• Stratum Granulosum
– Drastic changes in keratinocyte appearance
– Keratohyaline and lamellated bodies (waterproofing)
accumulate in cells
– Above this layer epithelial cells die because too far from
dermis
Layers of the Epidermis
• Stratum Lucidum
– Thin, transparent band superficial to S. Granulosum
– few rows of flat, dead keratinocytes
– only in thick skin (soles, palms)
• Stratum Corneum
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–
–
–
–
Outermost layer of keratinized cells
¾ of epidermal thickness
20-30 cell layers thick, all dead
Millions rub off everyday. Totally new every 25-45 days.
Functions:
• Waterproofing
• Protection from abrasion and penetration
• Rendering body relatively insensitive to biological, chemical, and
physical assaults
Fig. 5.2b
Fig. 5.3
Thick and Thin Skin
• all 5 epithelial
strata
– Stratum lucidum
– No hair
• Only 4 strata
• fewer cell layers
per stratum
– lucidum usually
absent
– Hair found only in
thin skin
Skin Color
• Melanocytes produce melanin inside
melanosomes (vesicles, from golgi), then
transfer melanin to keratinocytes
– size and distribution of melanosomes determine skin
color
– genetic but influenced by UV (tanning) and hormones
• Increased blood flow produces red skin color
(Erythema)
• decreased flow causes pale skin
– Decreased oxygen content in blood  bluish color
(cyanosis)
• Carotene, ingested plant pigment, can cause
skin to appear yellowish
Fig. 5.4
Dermis
• 2nd major skin region
• strong, flexible conn tissue
• Cell types: fibroblasts, a few adipose cells,
macrophages
• 2 layers:
– papillary
– reticular
Papillary layer of Dermis
– Areolar conn tissue w/collagen & elastic fibers
– superior surface- peg-like projections “dermal papillae”
• Genetic
• fingerprints & footprints
– Contains blood vessels that supply overlying epidermis
• With nutrients
• Remove waste products
• Aid in regulating body temperature
Reticular layer of Dermis
– Dense irregular conn tissue
– ~80% of thickness of skin
– Collagen fibers add strength and resiliency to
skin
– Elastin fibers provide stretch-recoil properties
– Striae (stretch marks) caused when skin
overstretched, dermis ruptures and leaves
visible lines
Reticular layer
– Elastin and collagen
fibers oriented more
in one direction than
in others
– produce cleavage, or
tension, lines
Fig. 5.5
Subcutaneous Tissue
• Deep to the skin
• Adipose (primarily) and areolar connective
tissue
• Not really part of skin
• Stores fat, connects skin to underlying
structures (mainly muscles)
• Shock absorber, insulator
• Increases as you gain weight
Hair
• Lanugo (fetal hair) replaced near time of birth by terminal
hairs (scalp, eyelids, eyebrows) and vellus hairs
• At puberty, vellus hairs replaced with terminal hairs
• Hairs are columns of dead, keratinized epithelial cells
– Each hair consists of
• shaft above skin
• root below skin
• hair bulb - site of hair formation
• growth stage and resting stage
• Contraction of arrector pili, smooth muscles, causes hair to
“stand on end”  “goose bumps”
Fig. 5.6
Sebaceous Glands
• Simple or compound alveolar glands
– found all over body except palms & soles
• Soften skin when stimulated by hormones
• Secrete oily secretion called sebum
• Acne: active inflammation of sebaceous
glands
Sweat Glands
• Different types prevent overheating of body
• Secrete cerumen and milk
• Up to 3 million/person
– Merocrine sweat glands produce sweat, cools body: most
numerous in palms and soles
– Apocrine sweat glands: axillary and genital areas. Ducts
empty into hair follicles. Produce organic secretion, broken
down by bacteria to cause body odor
– Ceruminous glands: modified merocrine glands in external
ear canal, secrete cerumen (ear wax)
– Mammary glands: specialized sweat glands, secrete milk
Fig. 5.7
Nails
• nail is Stratum Corneum containing hard
keratin
• nail root covered by skin
• nail body = visible part of nail
• Nearly all nail formed by nail matrix, but
nail bed contributes
• lunula = part of nail matrix visible through
nail body (white “crescent”)
Fig. 5.8
5 Integumentary System Functions
1. Protection
– Skin
• Protects against abrasion, UV
• Prevents entry of
microorganisms
• Helps regulate body
temperature
• Prevents water loss
– Hair
• Protects against abrasion, UV
• heat insulator
– Nails protect ends of digits
2. Sensation
– sensory receptors for
•
•
•
•
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heat
cold
touch
pressure
pain
Integumentary System Functions
3.Temp Regulation
– Skin
• Controls heat loss from
body (dilation and
constriction of blood
vessels)
– Sweat glands
• Produce sweat,
evaporates, lowers body
temperature
4. Vitamin D Production
• UV stimulates production of
a precursor molecule in skin
that’s modified by liver and
kidneys into vit D
• Vit D increases calcium
uptake in intestines
5. Excretion
• Skin glands remove small
amounts of waste products
but not important in
excretion
Blood Vessel Dilation, Fig. 5.9
Cancer: Basal Cell Carcinoma
• Least malignant and most common skin cancer
• Stratum Basale cells proliferate and invade dermis and
hypodermis
• Slow growing, do not often metastasize
• 99% Can be cured by surgical excision
Squamous Cell Carcinoma
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Arises from keratinocytes of Stratum Spinosum
Arise most often on scalp, ears, lower lip
Grows rapidly, metastasizes if not removed
Prognosis is good if treated by radiation therapy or
removed surgically
Melanoma
• Cancer of
• most dangerous type of skin cancer because it is:
– Likely to metastasize
– Resistant to chemotherapy
Melanomas
• ABCD rule
– A: Asymmetry; the 2 sides of pigmented area do not
match
– B: Border irregular w/indentations
– C: Color (pigmented area) is black, brown, tan,
sometimes red or blue
– D: Diameter larger than 6 mm (size of a pencil
eraser)
• Treated by wide surgical excision accompanied
by immunotherapy
• Chance of survival is poor if lesion is over 4 mm
thick
Burns
• First-degree: only epidermis is damaged
– localized redness, swelling, pain
• Second-degree: epidermis and upper regions of
dermis damaged
– Symptoms mimic first degree burns
– blisters also appear
• Third-degree: entire thickness of skin is damaged
– Burned area appears gray-white, cherry red, or
black;
– no initial edema or pain
• nerve endings are destroyed
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Rule of Nines
• Estimates severity of
burns
• Divides body into
areas
~ 9%, or multiples of 9%,
of total body area
• Younger patients are
different
• Burns considered
critical if:
– Over 25% of body has
2nd degree burns
– Over 10% of body has
3rd degree burns
– 3rd degree burns on
face, hands, or feet
Effects of Aging on the
Integumentary System
• Epidermal replacement of cells slows and skin
becomes thinner
• Decreased elasticity and loss of subcutaneous
tissue leads to wrinkles
• Subcutaneous fat layer diminishes, leading to
intolerance of cold
• Skin becomes dry and itchy
• Sweat and sebaceous glands are less active
• number of melanocytes decreases
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119