INTEGUMENT Skin is the largest organ in the body. Makes up 16%
of total body weight. Integumentary system describes the skin and
its appendages Hair Nails Skin glands
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STRUCTURE OF SKIN Classified as a cutaneous membrane Two
primary layers Dermis (inner) Epidermis (outer) Subcutaneous layer
Below the dermis rich in fat Thick and thin skin Thick skin- soles
and palms (4-5mm thick) Thin skin- covers most of the body (1-3mm
thick)
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EPIDERMIS
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EPIDERMIS- CELL TYPES Keratinocytes make up 90% of cells
present- principal structural element of OUTER skin Melanocytes
pigment producing cells (5% of total epidermal) give color and
filter UV light Langerhans cells play a role in immune
response
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CELL STRATA (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
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CELL STRATA- 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.
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LAYERS OF THE EPIDERMIS
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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.
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SKIN COLOR Basic determinant is quantity of melanin found in
the stratum basale of the epidermis in all races. Melanin is formed
from melanocytes using the amino acid, tyrosine. Albinism-
congenital absence of melanin.
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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)
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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
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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.
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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.
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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
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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.
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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. Langers 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
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FUNCTIONS OF THE SKIN 1. 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
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FUNCTIONS OF SKIN CONT. 2. Sensation- sophisticated sense organ
Able to detect temperature, pressure, touch, pain and other general
senses. http://www.innerbody.com/image_nerv16/nerv141.html 3.
Movement without injury due to elastic nature of skin 4. Excretion
of water, urea, ammonia, and uric acid 5. Vitamin D production
(Endocrine Function) Exposure to UV light converts 7
dehydorCHOLESTEROL to cholecalciferol (precusor to vit D) Vitamin D
is classified as a hormone once process is complete
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FUNCTIONS OF SKIN 6. Immunity Phagocytic cells destroy bacteria
Langerhans cells trigger helpful immune reaction with helper T
cells. 7. Homeostasis of body temperature Heat production must
equal heat lost for temperature to be balanced Heat production-
metabolism of foods in skeletal Muscle and liver. Chief determinant
is the amount of muscular work being done.
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FUNCTION OF SKIN: HOMEOSTASIS OF BODY TEMP 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
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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.
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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.
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BURNS- RULE OF NINES Head/neck - 9% Each arm - 9% Anterior
thorax - 18% Posterior thorax - 18% Each leg - 18% Perineum -
1%
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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
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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
scaring common Partial thickness burn
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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
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BURNS
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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 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
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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
http://www.innerbody.com/image_nerv16/nerv141.html
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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
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SKIN GLANDS- SEBACEOUS GLANDS Secrete sebum- oily substance
that keeps hair and skin soft 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
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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
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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 bodys ability to cool
itself