Chapter 6
Skin and the Integumentary
System
• Composed of several tissues
• Maintains homeostasis
• Protective covering
• Retards water loss
• Regulates body temperature
• Houses sensory receptors
• Contains immune system cells
• Synthesizes chemicals
• Excretes small amounts of waste
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Skin Cells
• help produce Vitamin D needed for
normal bone and tooth development
• some cells (keratinocytes) produce
substances that simulate development of
some WBCs
2
Types of Epithelial Membranes
Mucous
Serous
• line body cavities
that do not open to
the outside
• reduce friction
• inner lining of
thorax and abdomen
• cover organs of
thorax and abdomen
• secrete serous fluid
• line tubes and organs
that open to outside world
• lining of mouth, nose,
throat, etc.
• secrete mucus
Cutaneous
•covers body
• skin
Synovial
• composed entirely of
connective tissue
• lines joints
3
Layers of Skin
• Epidermis
• Dermis
• Subcutaneous layer
• beneath dermis
• not part of skin
4
Epidermis
• lacks blood vessels
• keratinized
• thickest on palms and soles (0.8-1.4mm)
• melanocytes provide melanin
• rests on basement membrane
• stratified squamous
5
• Production of new cells is balanced with the
loss of dead cells
• Protects underlying tissues against water
loss, mechanical injury, and the effects of
harmful chemicals
• Epidermal cells keratinize and die as they
are pushed to the surface
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Epidermis
Layers of Epidermis
• stratum corneum (dead cells)
• stratum lucidum
• stratum granulosum
• stratum spinosum
• stratum basale (reproduce and grow)
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8
Dermis
• on average 1.0-2.0mm thick
• contains dermal papillae
• binds epidermis to underlying
tissues
• irregular dense connective tissue
• muscle cells
• nerve cell processes
• specialized sensory receptors
• blood vessels
• hair follicles
• glands
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10
Subcutaneous Layer
• hypodermis
• loose connective tissue
• adipose tissue
• insulates
• major blood vessels
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Hair Follicles
• epidermal cells
• tube-like depression
• extends into dermis
• hair root
• hair shaft
• hair papilla
• dead epidermal cells
• melanin
• arrector pili muscle
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• A hair usually grows for a while, rests, and
then is replaced by a new hair.
• Hair color is determined by genes that direct
the type and amount of pigment epidermal
melanocytes produce
• A bundle of smooth muscle cells forms the
arrector pili muscle and attaches to each
hair follicle
• One or more sebaceous glands are attached
to each hair follicle
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Nails
• protective coverings
• nail plate
• nail bed
• lunula
•made of specialized
Epithelial cells that
keratinize
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Sebaceous Glands
• usually associated with hair
follicles
• holocrine glands
• secrete sebum
• Excess sebum causes acne
• absent on palms and soles
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Sweat Glands
• sudoriferous glands
• widespread in skin
• originates in deeper dermis
or hypodermis
• eccrine glands
• apocrine glands
• ceruminous glands
• mammary glands
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Eccrine sweat glands
• Most numerous
• Found on the forehead, neck, back, palms, and
soles
• Respond to elevated body temp or emotional
stress
• Sweat and sebaceous gland activity decreases with
advancing age
• Sweat is mostly water with salts and waste
products
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Apocrine Sweat Glands
• Become active at puberty
• Located in the axillary regions (armpit),
groin, and around the nipples
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• Ceruminous glands are modified sweat
glands that secrete earwax
• Mammary glands are modified sweat glands
that secrete milk
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21
Regulation of Body
Temperature
• Regulation of body temperature is vital
because heat affects the rates of metabolic
reactions. Normal temperature of deeper
body parts is close to a set point of 37°C
(98.6°F). Skin plays a key role in body
temperature homeostasis.
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Heat production and loss
• Heat is a by-product of cellular respiration.
• The most active cells are skeletal and heart
muscle cells and the liver.
• If body temperature rises above normal:
-more blood enters dermal blood vessels
(vasodilation).
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If body temperature rises above
normal:
• more blood enters dermal blood vessels
(vasodilation).
• deeper blood vessels contract
(vasoconstriction) diverting blood
to the surface and the skin reddens
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heat is lost to the outside by:
• radiation - rays move from warmer to cooler
surroundings (primary way)
• conduction - heat moves from warmer
objects to cooler objects it is touching
• convection - heated air moving away from
the body
• evaporation - fluid evaporates from the
surface carrying heat away (sweating)
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If the body temperature drops
below normal:
• dermal blood vessels constrict, causing the
skin to lose color
• sweat glands become inactive
• if heat is lost excessively, skeletal muscles
involuntarily contract increasing cellular
respiration and producing additional heat.
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Problems in Temperature
Regulation
Hyperthermia – abnormally high body temperature
Hypothermia – abnormally low body temperature
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• If the air is saturated with water, sweat may
fail to evaporate, and body temperature may
remain elevated (hyperthermia)
• Symptoms may begin with headache,
dizziness, nausea, muscle cramping, and
may lead to major organ failure
• Lack of sweating – medical emergency
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• Hypothermia is lowered body temperature.
• Symptoms begin with shivering, and leads
to mental confusion, lethargy, loss of
reflexes and ,consciousness, and eventually
major organ failure
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Skin Color
• All humans have about the same number of
melanocytes. Skin color differences are due
to the amount of melanin produced
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Genetic factors
• Genes that control melanin production are
inherited.
• Dark skin is due to genes that cause large
amounts of melanin to be produced
• Lighter skin is due to genes that cause lesser
amounts of melanin to form.
• Mutant genes may cause a lack of melanin
in the skin (albinism).
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Environmental factors
• Sunlight, ultraviolet light, and X rays
darken existing melanin and stimulate more
melanin production temporarily darkening
the skin.
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Physiological factors
• If blood is well oxygenated hemoglobin
(blood pigment) is bright red causing the
skin of light complected people to appear
pinkish.
• If oxygen content of blood is low
hemoglobin is dark red and the skin appears
bluish (cyanosis).
• Dilated blood vessels can cause skin to
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redden
• Constricted blood vessels cause a loss of
reddish color.
• Carotene in the subcutaneous layer may
cause the skin to appear yellowish.
• • Disease may affect skin color.
34
Healing of Wounds and Burns
• Skin injuries trigger inflammation. Blood
vessels dilate forcing fluids to leave and
enter the damaged tissue. The affected area
becomes red, warm, swollen, and tender.
35
Cuts
• A shallow cut in the epidermis is filled in by
reproducing epithelial cells.
• Deeper cuts into the dermis or subcutaneous
layer cause a clot to form.
• platelets become entrapped in protein fibers
(fibrin).
• tissue fluids seep into the area
• blood clot and dried fluids form a scab
36
• fibroblasts begin to form new collagenous
fibers that bind edges of the wound together
• blood vessels extend beneath the scab
• phagocytes remove dead cells
• a scar where connective tissue replaces skin
may appear
37
• granulations (new blood vessel branch &
fibroblasts) may form in large open wounds
38
Healing of Cuts
39
First degree burns (superficial
partial-thickness burn)
• only burns the epidermis
• heals quickly with no scarring
• the area is warm and red.
40
Second degree burns (deep
partial-thickness burn) –
• destroys some epidermis and dermis
• blisters appear
• area becomes moist and firm and varies in
color from dark red to waxy white
41
• healing depends on the accessory organs
that survive
• skin usually recovers with no scar tissue
unless an infection occurs.
42
Third degree burns
(full-thickness burns)
• destroys the epidermis, dermis, and the
accessory organs of the skin
• injured skin may appear dry and leathery
and varies in color from red to black to
white
• healing only occurs from epithelial cells
growing inward from the margin of the burn
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• may require skin grafting:
• autograft - thin layer of skin from unburned
area is removed and transplanted in injured
area
• homograft - cadaveric skin is used to cover
injury
• skin substitutes
- amniotic and artificial membranes human
skin cultures
- grow in lab and transplant
• extensive scarring
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Rule of Nines
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Life Span Changes
• Skin becomes scaly
• Age spots appear
• Epidermis thins
• Dermis becomes reduced
• Loss of fat
• Wrinkling
• Sagging
• Sebaceous glands secrete
less oil
• Melanin production slows
• Hair thins
• Number of hair follicles
decrease
• Nail growth becomes impaired
• Sensory receptors decline
• Body temperature unable to be
controlled
• Diminished ability to activate
Vitamin D
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Clinical Application
Acne Vulgaris
•most common skin disorder
•sebum and epithelial cells clog glands
•produces whitheads and blackheads (comedones)
•anaerobic bacteria trigger inflammation (pimple)
•largely hormonally induced
•androgens stimulate sebum production
•treatments include antibiotics, topical creams, birth control pills
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