Skin and Its Appendages
Chapter 6
Integument
 Skin is the largest organ in the body. Makes up 16% of
total body weight.
 Approximately 1.6-1.9 m2 in the average sized adult
 Integumentary system describes the skin and its
appendages
 Hair
 Nails
 Skin glands
Structure of Skin
 Classified as a cutaneous membrane
 Two primary layers- dermis and epidermis joined by a
dermal epidermal junction
 Subcutaneous layer- hypodermis or superficial fascia lies
beneath the dermis
 Thick and thin skin
 Thick skin- soles and palms (4-5mm thick)
 Thin skin- covers most of the body (1-3mm thick)
Epidermis
Epidermis- Cell types
 Keratinocytes- make up 90% of cells present- principal
structural element of outer skin
 Melanocytes- pigment producting cells (%5 of total) give
color and filter UV light
 Langerhans cells- play a role in immune response
Cell Layers of Epidermis
1. Stratum Corneum (top layer)
 Dead cells filled with keratin (barrier area)
2. Stratum Lucidum (clear layer)
cells filled with keratin precursor called eleidin absent in thin
skin.
3. Stratum granulosum (granular layer)
cells arranged 2-3 layers and filled with keratohyalin granules
that contain a high # of lysosomes ( to digest the cytoplasm as it
is replaced with keratin)
Cell layers- epidermis continued
4. Stratum Spinosum (spiny layer)
cells arranged in 8-10 layers with prominent desmosomes
(strong connections between cells appear spiny in
microscope): Rich in RNA which is necessary for the protein
synthesis of Keratin.
5. Stratum basale (base layer)
single layer of columnar cells: only these cells undergo
mitosis and then migrate through the other layers until they
are shed.
Layers of the epidermis
Epidermal growth and repair
 Turnover or regeneration time refers to time it takes for cells
to go from base layer to corneum. This takes about 35 days
 Shortened turnover time can be created with abrasion.
However prolonged abrasion of an area that stimulates
mitotic division results in a callus (increased stratum
corneum)
 Normally 10-12% enter mitosis daily in the stratum basale.
Dermis Epidermis junction
 A definite basement membrane, specialized fibrous elements
and a polysaccharide gel serve to “glue” the epidermis to the
dermis.
 The junction serves as a partial barrier to the passage of some
cells and large molecules
Dermis “TRUE SKIN”
 Much thicker
 Gives strength to the skin
 Reservoir storage area for water
and electrolytes
 Contains specialized sensory
receptors, muscle fibers hair
follicles, sweat and sebaceous
glands and blood vessels.
Dermis cont…
 Rich vascular supply plays a critical role in the regulation of
body temperature.
 As the body senses an increase in temperature the blood vessels
of the skin dilate and heat radiates out of the blood vessels
through the dermis (vasodilation)
 As the body senses a decrease in temperature the blood vessels
will constrict (vasoconstriction). This keeps warmer blood
circulating deeper in the tissue in more “critical” areas.
Layers of the Dermis
 Papillary layers- composed of
dermal papillae that project
into the epidermis; contains
fine collagenous and elastic
fibers; contains the dermal
epidermal junction ; forms a
unique pattern that gives
individual fingerprints
Layers of dermis cont…
 Reticular layer- contain dense, interlacing white collagenous
fibers and elastic fibers to make the skin tough yet
stretchable; when processed from animal skin it produces
leather.
Dermal Growth and Repair
 The dermis does not continually shed and regenerate itself as
does the epidermis
 During wound healing the fibroblasts begin forming and
unusually dense mass of new connective fibers; if not
replaced by normal tissue, this mass remains a scar.
 Langer’s cleavage lines patterns formed by the
collagenous fibers of the reticular layer of the dermis.
Important for surgeons
 If the elastic fibers of the dermis are stretched too much as in
obesity or pregnancy or rapid growth phases the result is tiny
linear markings or stretch marks- actual tears in the elastic
Skin Color
 Basic determinant is quantity
of melanin, found in the
stratum basale of the
epidermis in all races.
 Melanin is formed from
melanocytes from the amino
acid tyrosine.
 Albinism- congenital absence
of melanin.
Skin color cont…
 Process of skin coloration is regulate by tyrosinase(enzyme
that breaks down tyrosine) , exposure to sunlight, and certain
hormones including ACTH (adrenocorticotropic hormone)
that regulates aging.
 Carotene (yellowish color) can also contribute to skin color
 Color changes also occur as a result of changes in blood flow
to skin and circulating levels of unoxygenated hemoglobin.
(bluish to pale appearance)
Functions of the skin
 Protection
 Prevent dehydration
 UV barrier through melanin
 Surface film- sweat, oil, epithelial cells that are shedding
 Antibacterial, antifungal activity
 Lubrication
 Hydration of skin surface
 Buffer caustic agents
 Blockade of toxic agents
Functions of skin cont.
 Sensation- sophisticated sense organ
 Able to detect temperature, pressure, touch , pain and other
general senses.
http://www.innerbody.com/image_nerv16/nerv141.html
 Movement without injury due to elastic nature of skin
 Excretion of water, urea, ammonia, and uric acid
 Vitamin D production
 Exposure to UV light converts 7 dehydorCHOLESTEROL to
cholecalciferol (precusor to vit D)
 Vitamin D is classified as a hormone once process is complete
Functions of skin
 Immunity
 Phagocytic cells destroy bacteria
 Langerhans cells trigger helpful immune reaction with helper T
cells.
Homeostasis of body temperature
1. Heat production must equal heat lost for temperature to be
balanced
2. Heat production- metabolism of foods in skeletal Muscle and
liver. Chief determinant is the amount of muscular work
being done.
Function of skin: homeostasis of body
temp
 3. Heat Loss- approximately 80% of heat loss occurs through
the skin; remaining 20% occurs through the skin mucosa of
the respiratory, digestive, and urinary tracts.
 Evaporation- to evaporate fluid from skin energy must be
expended (sweat)
 Radiation- heat loss in cool environmental conditions
 Conduction-very small amounts of heat loss
 Convection- transfer of heat away from skin by movement of air
(sitting under a fan or air conditioner)
 Fig 6-6 pg 173
Homeostatic regulation of heat loss
 Heat loss is controlled by a negative feed back loop
 Hypothalamus senses temperature change from its “set point”
 If too high- signal sent to sweat glands and blood vessels
 If too low- to muscles to shiver to create frictional heating
 Once temperature is returned to set point nervous response is
inhibited.
BURNS- figure 6-9 p 176
 Injury or death to skin cells caused by heat, UV, electrical
current or corrosive chemical
 Severity is determined by depth of lesion and % of body
surface burned
 Estimating burn area
 RULE OF PALMS- palm is approximately 1% of body surface
 Lund-Browder Charts- more accurate with children due to the
difference in proportions of head to body.
Burns- Rule of NINES
 Head/neck - 9%
 Each arm - 9%
 Anterior thorax - 18%
 Posterior thorax -
18%
 Each leg - 18%
 Perineum - 1%
First degree burn
 Minor pain – no significant tissue destruction
 Some reddening of the skin
 No blistering, bust some peeling of surface occurs
 No scarring
 Typical sunburn
 Partial thickness burn
Second degree burn
 Severe pain
 Damage or destruction of epidermis and upper dermal layers
 Blisters form with swelling and edema (fluid in the tissue)
 Dermal tissue death not complete but scarring common
 Partial thickness burn
Third degree burn- full thickness burn
 Total destruction of both epidermis and upper dermal layers
 Tissue death extends below level of hair follicles and sweat
glands
 No immediate pain; nerve endings are destroyed
 Burning may involve deep tissues , including muscle and
bone
 Scarring is a serious problem
Burns
Appendages of the Skin
 Hair
Papilla- capillaries clustered under follicle
Root- tip of hair embedded in follicle
Shaft- visible part of hair
Medulla- inner core of hair: Cortex- outer portion
Color- results from the different amounts of melanin in cortex
of hair
 Growth- periods of growth and rest. Grows about 5 inches per
year.
 Sebaceous glands- oil glands that secrete sebum into follicle
 Male pattern baldness
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Appendages cont…
 Nails
 Epidermal cells converted to hard
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keratin
Nail body – visible part of each nail
Root- part of nail in groove hidden by
fold of skin, cuticle
Lunula- moon-shaped white area of
nearest root
Nail bed- layer of epithelium under
nail body- abundant blood vessels
Growth average: 0.5mm per week or
1 inch per year
Appendages cont. . . SKIN GLANDS
 Two types of sweat glands
 Eccrine glands
 Most numerous sweat glands, quite small
 Over total body surface
 Simple coiled tubular glands
 Function entire life
 Help body maintain temperature
 http://www.innerbody.com/image_nerv16/nerv141.html
Sweat Glands cont…
 Apocrine glands
 Located deep in subcutaneous layer
 Limited distribution- axilla, areola of breast, anus
 Large 5mm in diameter
 Simple branched tubular glands
 Function at puberty
 Secretion cyclic changes in female with menstrual cycle
Skin Glands- Sebaceous glands
 Secrete sebum- oily substance that keeps hair and skin soft
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and pliant; prevents water loss
Lipid components have antifungal activity
Simple branched glands
In dermis except for palms and soles
Secretion increases in adolescence forming pimples,
blackheads
Ceruminous glands
 Modified apocrine sweat glands
 Simple coiled, tubular glands
 Empty contents into external ear canal alone with sebaceous
glands
 Mixed secretions result in ear wax
 Functions to protect area from dehydration.
 Excess production can block ear canal and cause loss of
hearing
Cycle of Life: skin
 Children
 Smooth skin, elasticity, and flexibility
 Few sweat glands
 Rapid healing
 Adult
 Activation of sweat and sebaceous glands
 Increased sweat and body odor
 Increased sebum production (oil)= acne
 Old age
 Decreased sweat and sebaceous activity
 Wrinkling
 Decreased in the body’s ability to cool itself