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Reading assignment:
Chapter 6
(Thibodeau & Patton
Anatomy
& Physiology) |
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ACT
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Interactive
activity |
GA |
Gray's Anatomy |
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Animation |
pp |
PowerPoint
slide |
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FIG
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Figure |
term |
Define,
pronounce |
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Online preview:
Skin
(Previews are found at
WebCT)
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Integumentary system
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Integument = skin |
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Only one organ in this system --but it's the largest
organ of the body
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Therefore, the skin is an organ AND a system |
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Functions of skin
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Protection - mechanical, UV radiation, immune
"first line" and "second line," water
conservation |
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Excretion - sweat glands excrete
"waste" |
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Chemical synthesis - vitamin D |
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Thermoregulation - can regulate heat loss or
conservation |
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Sensation - various sense of touch, temperature,
vibration, pain |
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General structure
GA
pp
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Epidermis - stratified squamous epithelial outer
layer |
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Dermis - dense fibrous connective inner layer
(usually thicker than the epidermis) |
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Hypodermis - loose fibrous tissue under skin
(hypodermis is NOT part of skin, but where else can we discuss
it?) |
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Thickness varies
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Thick skin - Thickest skin found on palms,
fingertips, sole |
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Thin skin - Thinnest skin found on scalp,
near lips |
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Thick skin
microscopic section
Click to enlarge
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Thin skin
microscopic section
Click to enlarge
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Epidermis
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Composed of different strata, the outermost of which
are comprised of dead cells
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Cells divide only in base layer, then die as they
are pushed outward |
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Form a "keratinized" layer on surface
that protects |
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Strata (listed from deep to superficial)
GA
pp
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Stratum germinativum ("growth
layer")
- made up of two sublayers:
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Stratum basale ("base layer")
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Keratinocytes
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Keratin (tough, water-resistant
protein) |
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Melanocytes
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Melanin (brown protein pigment) is
produced by melanocyte cells in base layer
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Melanin, being dark, absorbs UV radiation |
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Melanin is released by
melanocytes, which have long extensions, and absorbed into surrounding
keratinocytes |
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Two categories of melanin:
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Eumelanins - dark brown |
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Pheomelanins - light
brown/red/orange |
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Cells of stratum basale are closest to
the blood supply in the dermis and are thus the healthiest
pp
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Only these cells can reproduce |
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Stratum spinosum ("spiny layer")
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Cells are pushed from below and become
"squished" and look "spiny" on cross
sectional view |
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Because the cells are farther away from
the dermal blood supply, they are less healthy and thus
don't reproduce |
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Cells get sicker and sicker as they are
pushed away from the dermis |
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Stratum granulosum ("grainy layer")
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As cells from stratum germinativum die,
they enter stratum granulosum |
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All cells here are dead (and look grainy
when stained/ no nuclei) --but biochemical changes are
happening inside them
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Keratohyalin (a precursor to
keratin) forms in granules here |
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Stratum lucidum ("light
layer" or "clear layer")
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Keratohyalin is transformed into eleidin,
which is almost transparent, making this layer look almost
"clear" |
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Stratum corneum ("horny layer"
meaning "like an animal's horn" --not what YOU were
thinking!)
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Keratin is fully formed |
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Flattened cells filled with keratin form
"keratinized layer" and make this "keratinized
stratified squamous epithelium" |
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Dermis
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Epidermis joins dermis at the glue-like dermal-epidermal
junction |
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Dermis is irregular dense fibrous connective tissue |
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Two layers of the dermis:
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Papillary region
GA
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Outer (superficial) region of dermis has bumps called dermal
papillae
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FYI - bumps in the human body are OFTEN called
papillae (sing. papilla = "nipple") |
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Increase surface area for glue to
"hold" more tightly |
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Arranged in rows to form "prints" of
hands/fingers and feet/toes to improve grip (and to identify the
perpetrators of crimes against professors) |
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Reticular region
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Deeper area of the dermis has irregular
swirls of collagen fibers plus nerves and nerve endings, blood
vessels, sweat glands, and more |
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Reticular = "network" |
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Scars
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Form when a
denser-than-usual mass of fibers are produced to replace
those damaged in an injury |
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Keloid scars are
abnormally large scars |
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Stretch marks occur when
the skin is overstretched and the dermis tears beneath the
epidermis
pp |
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Read about dermal cleavage
lines in the textbook |
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Hypodermis
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Also called "subcutaneous tissue" (sub =
"under" cutaneous = "skin") |
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Also called "superficial fascia"
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Fascia ( = "gang") is made up of loose
bundles ("gangs") of fibers |
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Superficial fascia is under the skin; deep fascia is
among the muscles |
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Loose fibrous tissue
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areolar (loose, ordinary) |
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adipose (formed when fat cells of areolar tissue grow
large and dominate the tissue) |
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NOT part of skin proper |
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Functions
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Protection |
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Thermoregulation |
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Shape |
 | Storage of fat (fuel
storage) |
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Recommended
link: Skin
Histology This is a brief set of
microscopic images to help you understand the structure of the skin
Hint:
You will be tested on the correct anatomical order of any/all layers of
the skin and associated structures (deep -> superficial AND superficial
-> deep) |
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General structure of the skin
Microscopic cross section
Click to enlarge
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Derivatives of skin
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Hair
GA
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Grows from hair follicles (follicle = "little
pocket")
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Hair papilla is bump at base of pocket
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Covered with stratum germinativum |
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Place from which the hair grows |
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Arrector pili
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Small muscles attached to follicle and
dermal-epidermal junction |
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Contract when a person is chilled or stressed
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Additional
arrector muscles in the skin around the nipple cause
the nipple to become erect
pp |
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A&P trivia: do you
know what the word horripilation means?
(click it to find out!) |
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Hair shaft (visible part) and root (not seen; in
follicle) GA
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Dense, cylindrical modification of keratinized
layer |
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Inner part: medulla |
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Outer part: cortex |
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Shape can affect curling (flatter = curlier) |
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Usually pigmented with melanin
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except in white
hair (such as in the platinum blonde highlights sported by your
professor) |
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cortex can be pigmented differently than medulla |
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Hair follicle
longitudinal section
Click to enlarge |
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Hair follicle
cross section
Click to enlarge
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Nails
GA
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Platelike, denser version of hair (never pigmented
in humans) |
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Nail body is visible part; nail root is still in follicle
(nail groove)
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Usually no pigmentation (easy to see changes in blood color
under nail)
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May have pigmented streaks |
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Lunula (= "little moon")
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Whitish crescent at base of nail |
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Base of nail root is fused with connective tissue
covering bone of finger- stabilizing nail |
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Nail bed is skin under the nail
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Stratum germinativum only |
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Human nail
Click to enlarge |
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Sweat glands (exocrine)
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Sweat contains mostly water plus some excretions
and secretions (such as pheromones [sex attractants]) |
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Different types
pp
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Eccrine - primarily thermoregulatory |
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Apocrine - involved in stress response |
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Sebaceous glands (exocrine)
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Secrete sebum or "skin oil"
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conditions hair
and skin to prevent damage |
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Surface film
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Combination of sweat, sebum, dead cells, bacteria, etc. |
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A mini ecosystem |
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Skin color
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Genetic factors (Example: inheritance of basic skin color,
freckles, albinism) |
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Environmental factors (Example: ultraviolet [UV]
radiation, dyes [tatoos])
pp |
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Physiological factors
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Examples:
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ß-carotenes from food |
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Hormones such as ACTH adrenocorticotropic
hormone |
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Blood volume/color
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Oxyhemoglobin is bright red;
carbaminohemoglobin is dark red |
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Cyanosis is bluish color of skin from
dark red blood |
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Jaundice (bile pigments build up in skin) |
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Click to enlarge
Left are Maasai girls from Tanzania, Africa.
Middle
are villagers from the upper Amazon, Peru.
Right is my daughter
Aileen in 1994. |
Human skin color varies widely, mostly
from the presence of different types and amounts of melanin in the
epidermis, as seen in these three photos of young girls. |
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A strange case
of the blues . . .Stan
Jones, the Libertarian candidate in Montana for the U.S. Senate in
2002, turned blue from taking home-made colloidal silver solution.
He took the solution as a preventive antibacterial agent. It
caused argyria,
which caused silver crystals to form in his skin which, along with
stimulated melanin production, made Mr. Jones's skin look gray-blue.
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Thermoregulatory functions of the skin
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Blood in the dermis is like the fluid in a radiator,
bringing heat from other parts of the body
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Blood flow in the dermis increases or decreases
as the body tries to gain or lose heat |
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Conduction
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Heat is conducted from blood through skin to air
(or water or the chair you are sitting on right now) |
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Convection
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Warm air rises (because it is less dense than
cool air), creating a convection current that draws cooler air in
behind it |
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Radiation
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Heat travels as radiant energy (like light or
radio waves), specifically as infrared (light waves beyond visible
red) |
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Evaporation
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When water turns to steam (evaporation) heat
moves (from skin) to the water molecules as they leave as water
vapor |
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Click each photo to enlarge
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The African elephant (above)
provides an extreme example of the skin's thermoregulatory function.
The front of the animal's ear (left photo) shows the ear's great size
relative to its head and body--but very thick skin. Notice the
lighter areas--these are highly keratinized patches. The back of the
ear reveals very large vessels near the surface of the very thin skin (no
light patches). The elephant can regulate heat loss through its ears
by exposing or not exposing the back of the ear. |
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Remember! Human body temperature
varies! |
| Carl
Wunderlich studied body temperatures of thousands of people way back
in 1868 and pronounced the average human body temperature (oral) to
be 98.6 °F (37.0 °C).
pp However, in 1992, P.A.
Mackowiak's research team used modern equipment and techniques and
found that the human body temperature (oral) averages about 98.2 °F
(36.8 °C). Here are their overall results:
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This Learning Outline may be
updated or improved at any time.
Check back frequently or use the
link to the right to inform you of changes. |
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© 1988-September, 2007 Kevin
Patton
ALL rights
reserved This page updated
09/27/07.
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