Download The Integumentary System

The Integumentary System
Chapter 5
The Skin
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A surface area of 1.5 - 2 square meters
Weighs approximately 4-5 kg (9-11 lbs.)
Every square centimeter contains:
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70 cm of blood vessels
55 cm of nerves
100 sweat glands
15 oil glands
230 sensory receptors
Half million cells that are constantly dying
and being replaced
The Skin
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Called the integument or covering, its
function is primarily protective
Forms the boundary between our
internal and the external environment
It is a pliable, tough, organ that is
constantly regenerating
Without skin we would succumb to
infection, water loss, or heat loss
Skin Layers
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Epidermis
– Outermost protective
shield of the body
– 1.5 - 4.0 mm in
thickness depending
on location
– Composed of
epithelial cells
– Avascular receives
nutrients that diffuse
from dermis
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Dermis
– Underlying skin layer
making up the bulk of
the skin
– A tough leathery
layer deep to the
epidermis
– Composed of fibrous
connective tissue
– Vascular
Hypodermis or superficial fascia
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A subcutaneous tissue deep to the skin
Not considered a part of the skin, but it
shares some of the skins protective functions
Consists mostly of adipose tissue and areolar
connective tissue
It functions to store fat, anchor the skin to
the underlying muscles, allowing for
movement
Hypodermis thickens markedly when one
gains weight
Hypodermis Fat Deposition
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Female
– Breasts
– Thighs
• Saddle bags
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Male
– Anterior abdomen
• Beer belly
– Waist
• Spare tire
Epidermis
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A thick keratinized layer of stratified
squamous epithelium
Consists of four distinct cell types
Arranged in four or five distinct cell
layers
Cells of the
Epidermis
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Keratinocytes
Melanocytes
Merkel cells
Langerhans’
cells
Keratinocyte
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Principle cell
of the
epidermis
Seen here
migrating
upward
through
various layers
of the
epidermis
Keratinocytes
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Most of the epidermal cells are keratinocytes
The chief role of keratinocytes is to produce
keratin, the tough fibrous protein that gives
the epidermis its protective qualities
Tightly connected by desmosomes
Keratinocytes arise from constant cell mitosis
at the deepest layer of the epidermis
Keratinocyte cells manufacture keratin
during their migration to the skin surface
Keratinocytes (continued)
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As cells migrate to the surface their
contents become dominated by keratin
The cells will deform to become flattened,
dead structures that are keratin filled
Million of cells on the free surface rub off
daily
A totally new epidermis every 25-45 days
Cell reproduction is higher in areas
subject to friction (hands, feet)
Melanocytes
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Spider shaped
cells found
Stratum
basale or
basal layer
Melanocytes
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Specialized epithelial cells that synthesize the
pigment melanin
Cells are found in the deepest layer of the
epidermis
Melancytes have many branching processes
that touch all keratinocytes in the basal layer
Processes carry melanin to keratinocytes
Melanin granules accumulate on the superficial side of the nucleus of the ketatinocytes
Melanocytes
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Melanin granules form a pigment shield
that protects the nucleus from ultraviolet
(UV) radiation in sunlight
All humans have the same amount of
melanocytes
Racial differences in skin coloring is
thought to be due to differences in
melanocyte activity, or the speed of
melanin break-down within the
keratinocytes
Langerhan’s
Cells
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Star shaped
cells among
keratinocytes
Langerhan’s Cells
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Cells arise from bone marrow and
migrate to the epidermis
The cells are macrophages that help to
activate the immune system
Their cell processes extend among
surrounding keratinocytes
From a continuous network
Merkel Cells
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Spiky shaped
hemispheres
found at the
epidermal dermal
junction
Merkel Cells
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Each Merkel cell is associated with a disc
shaped sensory nerve ending
The combined structure is called a
Merkel disc
Merkel discs function as a sensory nerve
receptor for touch
Epidermal
layers
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Four layers in
“thin skin”
Covers most
of the body
Epidermal
Layers
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Five layers
found in
“thick
skin”
Stratum
lucidum is
extra layer
Found on
fingertips,
palms and
soles of feet
Stratum
basale
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Deep layer
attached to
underlying
dermis
Singe row
of youngest
cells
Ongoing
cell mitosis
Stratum
spinosum
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Several cell
layers thick
Cells contain
a web-like
system of
filaments
Abundant
Langerhan’s
cells in this
layer
Stratum
granulosum
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Area of 3-5
cell layers
Ketatinocytes
flatten and
begin to
disintegrate
Release of
glycolipid
slows water
loss
Cell binding
Stratum
lucidum
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Consist of a
few rows of
clear, flat,
dead cells
Present
only in
thick skin
Stratum
corneum
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Broad zone
20-30 cell
layers thick
3/4 of
epidermal
thickness
Protects
skin from
abrasion &
penetration
Dermis
Dermis
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The dermis is the second major skin
region
Layer is strong, flexible connective tissue
Cells are typical of connective tissue
– Fibroblasts, macrophages, mast cells, and
white blood cells
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Semifluid matrix is heavily embedded
with collagen, elastin, and reticular fibers
It is your “hide”
Dermis
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Dermis is richly supplied with nerve
endings, blood vessels, and lymphatic
vessels
Hair follicles, oil and sweat glands, are
located in the dermis
Dermis has two main layers
– Papillary layer
– Reticular layer
Papillary layer
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A thin superficial connective tissue layer
in which the fibers form a loosely woven
mat heavily invested with blood vessels
Superior surface has projections called
dermal papillae that indent the overlying
epidermis
Many papillae contain capillary loops, in
others are free nerve endings (pain), and
Meissner’s corpuscles (touch)
Dermal ridges
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On the hands and soles of the feet the
papillae lie atop dermal ridges
The dermal ridges produce conspicuous
looped and whorled ridges on the
epidermal surface which increase the
grip of the fingers and feet
Sweat pores open along the crests of the
epidermal ridges leaving a film of sweat
we know as fingerprints
Reticular layer
Reticular layer
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This layer accounts for 80% of the dermis
Tissue is dense irregular connective tissue
Its extracellular matrix contains thick
collagen bundles running in various planes
Collagen fibers of the dermis give skin
strength and resiliency
Collagen binds water helping to maintain
hydration
Elastin provides stretch-recoil properties
Tension lines
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Collagen fibers tend to run parallel to the
skin surface
Separations in fibers yield lines of tension
Tension lines are significant for surgeon’s
and their patients
Incisions parallel to lines of tension gape
less than those made across the line of
tension
Dermal stretching
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During pregnancy dermal tearing may
occur indicated by silvery white scars or
“stretch marks”
Blisters are the separation of the
epidermal and dermal layers with the
resulting development of a fluid filled
pocket
Flexure lines
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Flexure lines are dermal folds that occur at
or near joints where the dermis is secured
to deeper structures
Folds are on the surface of the wrists,
palms, soles of the feet, fingers and toes
Since the skin cannot slide to accommodate
joint movement in such regions, the dermis
folds and skin creases form
Skin Color
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Three pigments contribute to skin color;
melanin, carotene, and hemoglobin
Melanin ranges in color from yellow to
reddish brown
Racial differences in skin coloring reflect
the relative kind and amount of melanin
Dark skinned people produce much more
and darker melanin than those of fair
skinned individuals and their ketatinocytes
retain it longer
Melanin
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Freckles and pigmented moles are local
accumulations of melanin
Melanocytes are stimulated to greater
activity when exposed to sunlight
Prolonged sun exposure causes a
substantial melanin buildup, which helps
protect DNA of viable skin cells from UV
radiation
A speed up of melanin production
resulting in a darkening of the skin (a tan)
Carotene
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Carotene is a yellow to orange pigment
found in plant products such as carrots
It tends to accumulate in the stratum
corneum and the fatty tissue of the
epidermis
It is most obvious on the palms and soles
of the feet where the stratum corneum is
thickest
Color is more intense when large amount
of carotene rich foods are eaten
Hemoglobin
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The crimson color of oxygenated
hemoglobin gives fair skin its pinkish hue
The hemoglobin is located in red blood
cells circulating in the dermal capillaries
Caucasians have only a small amount of
melanin, the dermis is nearly transparent
and the hemoglobin’s color shows through
When hemoglobin is poorly oxygenated the
blood and skin of light skinned people
appears blue
Skin color anomalies
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Redness - embarassment, fever, allergy,
inflammation or hypertension
Blanching - emotional stress, anemia, or
low blood pressure
Jaundice - liver disorder resulting in a
buildup of bile pigments
Bronzing - metallic appearance if skin is
due to hypofunction of the adrenal cortex
Black and blue - clotted blood masses
under the skin are called hematomas
Appendages of the Skin
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Sweat (Sudoriferous) glands
Sebaceous (oil) glands
Hair and hair follicles Nails
Nails
Sweat Glands
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Sweat glands are distributed over the
entire body surface except the nipples
and parts of the external genitalia
Approximately 2.5 million per individual
Two major types
– Eccrine sweat glands
– Apocrine sweat glands
Eccrine sweat glands
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The most numerous sweat gland
Particularly abundant on the palms, soles
of the feet, and forehead
Each is a simple, coiled, tubular gland
The secretory part lies coiled in the
dermis and the duct extends to open in a
funnel shaped pore
Sweat
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Sweat is a hypotonic filtrate of the blood
that passes through the secretory cells of
the sweat glands and is release by
exocytosis
It is 99% water with some salt (NaCl),
vitamin C, antibodies, traces of metabolic
wastes and lactid acid
Composition depends on heredity and diet
Normally sweat is acidic with a pH
between 4 and 6
Sweating
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Sweating is regulated by the sympathetic
divisions of the autonomic nervous system
Its major role is to assist in
thermoregulation and prevent overheating
of the body
Heat induced sweating begins on the
forehead and spreads inferiorly
Emotional sweating “cold sweat” is brought
on by fright, embarrassment, or
nervousness and begins on the palms, soles,
and axillae and then spreads over the body
Apocrine sweat glands
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Largely confined to the axillary and
anogenital areas
Apocrine sweat glands are larger than
eccrine sweat glands and their ducts
empty into hair follicles
Apocrine secretions contain the same
basic components as sweat plus some
fatty substances and protein
Bacteria upon our skin decompose these
substances and produce body odor
Ceruminous glands
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Ceruminous glands are modified
apocrine glands found in the lining of the
external ear
These glands secrete cerumen, or earwax,
which because of its sticky texture deters
insects and foreign material from
entering the ear
Mammary glands
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Mammary glands are another variety of
specialized sweat gland that secretes milk
Lobules within the breast produce milk
when a woman is lactating
Compound alveolar glands pass the milk
into the lactiferous ducts which open to
the outside of the nipple
Sebaceous (oil) Glands
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Sebaceous glands are simple alveolar
glands found all over the body except on
the palms and soles
The glands are small on the body trunk
and limbs, but quite large on the face,
neck and upper chest
These glands secrete an oil called sebum
Classified as holocrine glands they
secrete into a hair follicle or pore on the
skin surface
Sebaceous Glands (con’t)
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Sebum softens and lubricates the hair
and skin, prevents hair from becoming
brittle, and slows water loss from the skin
Sebum is bactericidal and reduces the
number of bacteria residing on the
surface of the skin
The glands are regulated by hormones
and while relatively inactive in childhood
become activated in both sexes during
puberty
Hairs and Hair Follicles
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The main function of our sparse body
hair is to sense insects on the skin before
they sting
Hair on the scalp protects against
trauma, heat loss, and sunlight
Eyelashes shield the eyes, and nose hairs
filter large particles like lint and insects
from the air
Structure of a Hair
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Hairs, or pili, are flexible strands
produced by hair follicles that consist of
largely keratinized cells
Hard keratin found in hair is tougher and
more durable than that found in
epidermal layers and does not flake
Structure of a Hair
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The hair shaft
projects from the skin
The root is embedded
in the skin
The shape of the shaft
determines whether
the hair is straight or
curly
– Flat / kinky
– Oval / smooth and
silky
– Round / coarse
Structure of a Hair
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A hair has three
concentric rings
– Medulla is the
central core of large
cells separated by
air spaces
– Cortex is the bulky
layer surrounding
the medulla
– Cuticle is a single
layer of overlapping
cells
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Melanin colors hair
Structure of a Hair Follicle
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Hair follicles
extend from the
epidermal surface
into the dermis
The deep end of
the follicle is
expanded and
forms a hair bulb
A sensory nerve
ending called a
root hair plexus
wraps each bulb
Structure of a Hair Follicle
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Papilla (a) protrudes
into a hair bulb and
supplies nutrients
The wall of the follicle is
made of an outer
connective tissue (b)
sheath and inner
epithelial root sheath (c)
A single layer of stratum
basale cells (d) divide to
form hair
b
c
d
a
Structure of a Hair Follicle
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Associated with
each hair follicle is
a bundle of
smooth muscle
fiber called
arrector pili
The muscle fibers
pull the hair shaft
into an upright
position
Hair Distribution
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Millions of hair are scattered over the
body
100,000 in the scalp and 30,000 in a beard
Only lips, parts of external genitalia, and
thick skin areas of hands and soles of feet
are free of hair
Hair Type
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Hair is classified as vellus or terminal
The body hair of children and women is
the fine vellus variety
Hair of the eyebrows and scalp is called
terminal hair
At puberty terminal hair appears in the
axillary and pubic regions of both sexes
Hair growth and density are influenced
primarily by nutrition and hormones
Hair Development
Hair Growth
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The rate of hair growth
varies from region to
region and with sex
and age, but averages 2
mm a week
Hair follicles go
through growth cycles
A growth cycle (a) is
followed by rest cycle
where the follicle
atrophies (b)
Hair Thinning and Baldness
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The rate of hair growth declines in the
fourth decade and reflects an age related
atrophy of hair follicles
Hairs are not replaced as fast as they are
shed and the result is a gradual thinning
and some degree of baldness (alopecia) in
both men and women
Coarse terminal hair are replaced by
vellus hair and the hair becomes
increasingly wispy
Male Pattern Baldness
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Male pattern baldness is a genetically
determined sex-influenced condition
Genes in adulthood changes the response
of hair follicles to testosterone
Follicle growth cycles shorten and many
hair never emerge before they are shed
by the follicle
Any hair present are of the finer, vellus
form
Nails
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Nails are scalelike
modification of the
epidermis that
forms a clear
protective covering
of the distal part of
the finger
Nails contain hard
keratin
Nails
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Nail components
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Free edge
Body of nail
Nail folds
Lunula
Eponychium
Nail matrix
The nail matrix lies
deep to the lunula
and is the site
where nail growth
is occurring
Integumentary System Functions
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Protection
– Chemical barrier
– Physical or Mechanical barrier
– Biological barrier
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Body Temperature Regulation
Cutaneous Sensation
Metabolic Functions
Blood Reservoir
Excretion
Protection
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Chemical barrier
– Skin secretions create an acid mantle that
retard bacteria reproduction
– Sebum from sebaceous glands is bactercidal
– Skin cells secrete a natural antibiotic call
human defensin
– Melanin shields the skin from UV radiation
Protection
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Physical or mechanical barrier
– Hard keratinized cells provide a continuous
barrier
– Glycolipids of the epidermis block the
diffusion of water and water soluble
substances from between cells
– Substances that do penetrate the skin in
limited amounts include
• Lipid soluble substances such as oxygen, carbon
dioxide and fat soluble vitamins (A, D, E, and K)
• Natural and manufactured solvents, salts, and
drugs
Protection
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Biological barrier
– Langerhans’ cells of the epidermis “present”
foreign substances (antigens) to the white
blood cells (lymphocytes) which in tern
activate our immune system
– Macrophages of the dermis dispose of
viruses and bacteria that have penetrate the
epidermis but they also work as presenters
Body Temperature Regulation
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The body works best when its
temperature remains within homeostatic
limits
Cooling occurs through radiation of heat
and evaporation of water from the surface
of the skin
Heating occurs from metabolism, activity
and shivering
Extremes of environmental temperature
threaten homeostatic balance
Cutaneous Sensation
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The skin is richly supplied with cutaneous
sensory receptors
Cutaneous receptors are classified as
exteroreceptors because they respond to
external stimuli
Cutaneous receptors include
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Meissner’s corpuscles (light touch)
Pacinian corpuscles (deep pressure
Root hair plexuses (displacement of hair shaft)
Free nerve endings (pain)
Metabolic Functions
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Sunlight bombarding modified
cholesterol molecules in the epidermal
cells are converted to a precursor of
vitamin D
Keratinocyte enzymes can “disarm”
many cancer causing carcinogens
Keratinocytes can also activate steroid
hormones
Blood Reservoir
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The skin can hold about 5% of the body’s
entire blood volume
Blood volume can be diverted from the
skin to other organs in need
Blood volume can be diverted to the skin
for temperature regulation
Excretion
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Limited amount of nitrogen-containing
wastes (ammonia, urea, and uric acid)
are eliminated from the body in sweat
Sweating also excretes water and salt
Homeostatic Imbalances of the Skin
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Homeostatic imbalances of the skin range
from mild to life-threatening
Homeostatic imbalances are readily
visible
There are over 1000 different conditions
and ailments affecting the skin
A select few will be presented
Burns
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Burns are a devastating threat to the
individual because of their effect on the skin
The threat to life severe burns is loss of body
fluids contain protein and electrolytes
Fluid loss can cause dehydration and
electrolyte imbalances
These in turn can lead to renal shutdown and
circulatory shock
The amount of fluid volume lost is estimated
using the rule of nines
Burns
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Estimating the area of a burn using the rule of 9’s
Classification of Burns
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Burns are classified according to their
severity (depth) as first second or third
degree
– 1st
– 2nd
– 3rd
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Only the epidermis is damaged
Epidermis and the upper dermis
Entire thickness of the skin
Partial thickness and full thickness burns
are a reference to the extent of skin layers
damaged
Basal Cell Carcinoma
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Least malignant
and most common
skin cancer
Cells of the stratum
basale proliferate
and invade the
dermis
Lesions appear as
shiny dome shaped
nodules
Excision result in a
99% cure rate
Squamous Cell Carcinoma
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Lesions arise from
the keratinocytes of
the stratum
spinosum
Lesion appears as a
scaly reddened
rounded elevation
Tends to grow
rapidly and
metastasize to
adjacent lymph
nodes
Malignant Melanoma
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Most dangerous
form of skin cancer
Melanoma can
develop wherever
there is pigment
Appears as a brown
to black patch that
metastasizes rapidly
to the adjacent
lymph and blood
vessels
50% survival rate
Skin Disorders - Anterior
Skin Disorders - Posterior
Medical Wounds
Developmental Aspects