Download THE SKIN - Archbishop Ryan High School

THE INTEGUMENTARY SYSTEM
• Complex set of organs that includes
the skin and its derivatives (sweat and
oil glands, hairs, and nails)
– Includes:
– Nerves
– Blood vessels
– Muscles
• Major function: protection
THE SKIN
• Also called the integument,
which simply means:
covering
• Epidermis:
– The epidermis is a keratinized
stratified squamous epithelium
(epi=upon)
– Outer most protective shield of
the body
• Dermis:
– Underlying epidermis
– Makes up bulk of skin
– Composed of:
• Fibrous connective tissue
• Blood vessels:
– Nutrients reach the
epidermis by diffusion
SKIN
THE SKIN
•
Hypodermis: also called superficial
fascia
–
Subcutaneous tissue:
•
–
–
–
Deep to the skin
Not really part of the skin but it
shares some of the skin’s protective
functions
Superficial to the tough connective
tissue wrapping (fascia) of the
skeletal muscles
Consists mostly of adipose tissue:
•
Stores fat:
–
–
–
–
Shock absorber
insulation
Anchors the skin to the underlying
structures (muscles)
Thickens as one gains weight:
•
•
•
Thighs
Breast
Beer belly
SKIN
Epidermis
• A keratinized stratified
squamous epithelium
consisting of four
distinct cell types and
four or five distinct
layers:
– Stratum Corneum
– Stratum Lucidum (thick
skin)
– Stratum Granulosum
– Stratum Spinosum
– Stratum Basale
Cells of the Epidermis
• Include:
–
–
–
–
Keratinocytes
Melanocytes
Merkel cells
Langerhan’s cells
EPIDERMIS
Cells of the Epidermis
Keratinocytes
•
•
•
Produce keratin
– Fibrous protein that helps give the epidermis its protective properties
Tightly connected to one another by desmosomes (cell junction
composed of thickened plasma membranes joined by filaments)
Arise in the deepest part of the epidermis from a layer of cells (stratum
basale) that undergo almost continuous mitosis
– Cells pushed upward by the production of new cells beneath them
– By the time they reach the free surface of the skin, they are dead,
scalelike structures that are little more than keratin-filled plasma
membranes
– Millions rub off everyday giving us a totally new epidermis every 25 to
45 days
• Friction rubs them off (hands, etc)
– Persistent friction causes a thickening of the epidermis called a
callus
EPIDERMIS
Cells of the Epidermis
Melanocytes
•
•
•
Spider shaped cells
Found in the deepest layer of the
epidermis
Synthesize the pigment melanin
(melan=black)
– Made and accumulated in
membrane-bound granules (small.
grainlike mass) called
melanosomes
• Moved along actin filaments by
motor proteins to the ends of the
melanocyte’s processes (spider
arms)
– From here they are taken up by
the keratinocytes
– Accumulate on the superficial
(sunny side) of the
keratinocyte nucleus, forming a
pigment shield that protects the
nucleus from the damaging
effects of ultraviolet (UV)
radiation in sunlight
EPIDERMIS
Cells of the Epidermis
Langerhan’s Cells
• Star-shaped
• Arise from bone
marrow and migrate to
the epidermis
• Also called epidermal
dendritic cells
• Are macrophages
(WBC) that help activate
our immune system
– Their slender processes
extend among the
surrounding keratinocytes,
forming a more or less
continuous network
EPIDERMIS
Cells of the Epidermis
Merkel Cells
• Present at the
epidermal-dermal
junction
• Saped like a spiky
hemisphere
• Intimately associated
with a disclike sensory
nerve ending:
– This combination is
called a Merkel disc
– Functions as a sensory
receptor for touch
EPIDERMIS
Layers of the Epidermis
• Variation in epidermal
thickness determines if skin is
thick or thin
• Thick skin covers: palms,
fingertips, and soles of the feet
– Five layers: strata (bed
sheets)
• Deep to superficial:
–
–
–
–
–
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
• Thin skin covers the rest of
the body
– Stratum lucidum is absent
and the other layers are
thinner
EPIDERMIS
Layers of the Epidermis
Stratum Basale
• Deepest epidermal layer
• Attached to the
underlying dermis along
a wavy borderline
• Consists (mostly) of a
single row of cells
representing the
youngest keratinocytes
• Many mitotic nuclei
– Reflects rapid cell
division
• Alternate name: stratum
germinativum
EPIDERMIS
Layers of the Epidermis
Stratum Spinosum
•
•
•
Spinosum (prickly)
Several cell layers thick
Cells contain a weblike system of
intermediate filaments, which span
their cytosol to attach to desmosomes
–
•
Keratinocytes appear irregular (spiny)
in shape, causing them to be called
prickle cells
–
–
•
These intermediate filaments consist
mainly of tension-resisting bundles of
prekeratin filaments
Spines do not exist in the living cells
They arise during tissue preparation
when these cells shrink but their
numerous desmosomes hold tight
Scattered among the keratinocytes
are:
–
–
Melanin granules
Langerhan’s cells (highest
concentration)
EPIDERMIS
Layers of the Epidermis
Stratum Granulosum
•
•
Consist of 3-5 layers in which keratinocyte
appearance changes drastically
– Cells flatten
– Nuclei and organelles begin to
disintegrate
– They accumulate:
• Keratohyaline granules:
– Help to form keratin in the
upper layers
• Lamellated granules:
– Contain a waterproofing
glycolipid that is spewed into
the extracellular space and
is a major factor in slowing
water loss across the
epidermis
– Cell membranes thicken
• Lipids coat the external
membrane
Above this layer the epidermal cells are
too far from the dermal capillaries, so
they die
EPIDERMIS
Layers of the Epidermis
Stratum Lucidum
• Thin translucent band
• Few rows of clear, flat,
dead keratinocytes with
indistinct boundaries
• Gummy substance of
the keratohyaline
granules clings to the
keratin filaments in the
cells, causing them to
aggregate in parallel
arrays (regular
arrangement)
• Visible ONLY in THICK
SKIN
EPIDERMIS
Layers of the Epidermis
Stratum Corneum
• Horny (hard, callous) layer
• 23-30 cell layers thick (3/4 of
epidermis)
• Keratin and the thickened
plasma membranes of cells
protect the skin against
abrasion and penetration
• Glycolipid between cells
waterproofs this layer
• The stratum corneum (horny
layer) is the outermost
protective layer of the
epidermis composed of a
thick layer of dead
keratinocytes
EPIDERMIS
SKIN
EPIDERMIS
Dermis
•
•
Composed of strong, flexible connective tissue
Its cells are typical of those found in any connective tissue proper:
–
–
–
–
–
Fibroblasts: cells that form the fibers of connective tissue
Macrophages: protective cell capable of phagocytosis
Mast cells: immune cell that initiates inflammation
White blood cells: protection
Its semifluid matrix is heavily embedded with:
• Collagen: strong, fibrous (threadlike) insoluble protein
• Elastin: extracellular connective tissue protein
• Reticular fibers: supporting framework tissue
•
The dermis binds the entire body together like a body stocking
– It is your hide and corresponds exactly to animal hides used to make
leather products
•
•
Richly supplied with nerve fibers, blood vessels, and lymphatic vessels
Major portions of hair follicles, as well as oil and sweat glands, are
derived from epidermal tissue but reside in the dermis
Dermis
Two Layers
• 1.The thin, superficial
papillary layer is highly
vascularized areolar
connective tissue containing a
woven mat of collagen and
elastin fibers
– Its superior surface is thrown
into peglike projections
called dermal papillae
(papill=nipple) that indent the
overlaying epidermis
• Many contain:
– Capillary loops
– Meissner’s corpuscles:
touch receptors
– Pain receptors
SKIN
Dermis
Two Layers
• On the palms of the hands
and soles of the feet, these
papillae lie atop larger
mounds called dermal ridges
– Which in turn cause the
overlying epidermis to form
epidermal ridges that
increase friction and enhance
the gripping ability of the
fingers and feet
• Epidermal ridge patterns
are genetically determined
and unique to each of us
• Because sweat pores open
along their crest, our
fingerprints leave
identifying films of sweat
called fingerprints on
almost anything they touch
SKIN
Dermis
Two Layers
• Three types of skin markings:
– Finger prints
– Cleavage lines
– Flexure lines
Dermis
Two Layers
•
2.The reticular layer:
– Deeper
– Account for 80% of the thickness of the
dermis
– Extracellular matrix contains thick bundles of
interlacing fibers that run in various planes
• Most run parallel to the skin surface
• Less dense regions, between these
bundles form cleavage, or tension
lines:
– Important to a surgeon:
» Incision made parallel to
these lines, the skin gapes
less and heals more
readily than when the
incision is made across
cleavage lines
– Collagen fibers give skin strength and
resiliency
• Binds water, helping keep the skin
hydrated
– Elastin fibers provide the stretch-recoil
properties of skin
SKIN
Dermis
Two Layers
• Flexure lines:
– Dermal folds that occur at or near joints,
where the dermis is tightly secured to deeper
structures (notice the deep creases on your
palms)
• Since the skin cannot slide easily to
accommodate joint movement in such regions,
the dermis folds and deep skin creases form
– Visible on wrists, fingers, soles, and toes
HOMEOSTATIC IMBALANCE
• Dermal tearing:
– Stretching of the skin during pregnancy
– Stretch marks
• Blister:
– Separation of the epidermal and dermal
layers by a fluid-filled pocket
Skin Color
• Determined by three pigments:
– Melanin
– Hemoglobin
– Carotene
Melanin
• Only pigment made in the skin
• Polymer of tyrosine amino acid
• Ranges in color from yellow to reddishbrown to black
• Synthesis depends on an enzyme in
melaocytes called tyrosinase
• Passes from melanocytes to the basal
keratinocytes
Melanin
• All humans have the same relative number of
melanocytes
– Individual and racial differences in skin coloring
reflect the relative kind and amount of melanin
made and retained
– Melanocytes of black and brown skinned people
produce many and darker melanosomes than
those of fair-skinned individuals, and their
keratinocytes retain it longer
• Freckles and pigmented moles are local accumulations
of melanin
Melanin
• Melanocytes are stimulated by sunlight
– Causes substantial melanin buildup, which
helps protect the DNA of viable skin cells from
UV radiation by absorbing the light and
dissipating the energy as heat
HOMEOSTATIC IMBALANCE
• Excessive sunlight damages the skin:
– Clumping of elastin fibers: results in leathery
skin
– Depresses the immune system
– Alters DNA
Carotene
• Yellow to orange pigment found in certain
plant products such as carrots
• Tends to accumulate in the stratum corneum
and in the tissue of the hypodermis
• Color most obvious in the palms and soles,
where the stratum corneum is thickest (example:
the skin of the heel)
• Most intense when large amounts of carotenerich foods are eaten
Hemoglobin
• Pinkish hue of fair skin people
Skin Color Variations
• Redness: erythema
–
–
–
–
–
Embarrassment
Fever
Hypertension
Inflammation
Allergy
• Pallor: blanching
–
–
–
–
–
Fear
Anger
Emotional stress
Anemia
Low blood pressure
• Jaundice: yellow cast
– Liver disorder (yellow bile
pigment accumulates in the
blood and deposited in body
tissues)
• Bile normally secreted in the
bile pigments (bilirubin) as
part of bile
• Bronzing:
– Metallic appearance of skin
– Addison’s disease
– Hyperfunction of adrenal
cortex
• Black and blue: bruises
– Blood escaping from the blood
vessels and clotting under the
skin
APPENDAGES OF THE SKIN
• Derivatives of the epidermis:
– Sweat Glands
– Sebaceous Glands
– Nails
– Hair
– Hair Follicles
Sweat (Sudoriferous) Glands
• Distributed over the entire skin surface
except the nipples and parts of the
external genitalia
• Two types of sweat glands:
– Eccrine
– Apocrine
Sweat (Sudoriferous) Glands
Eccrine Sweat Glands
• (b):Eccrine sweat glands, or merocrine sweat
glands, produce true sweat, are the most
numerous of the sweat glands, and are
particularly abundant on the palms of the hands,
soles of the feet, and forehead
CUTANEOUS GLANDS
CUTANEOUS GLANDS
Sweat (Sudoriferous) Glands
Eccrine Sweat Glands
• Also called merocrine sweat glands
• Abundant on the palms, soles of feet, and forehead
• Simple, coiled, tubular gland Secretory part lies coiled in the
dermis:
– The duct extends to open in a funnel-shaped pore at the skin surface
• Secretion commonly called sweat is a:
– Hypotonic filtrate (lower osmotic pressure than a reference) of the
blood that passes through the secretary cells of the sweat glands and is
released by exocytosis
– 99% water, with some salts (mostly sodium chloride)
– Vitamin C
– Antibodies
– Dermicidin: microbe-killing peptide
– Traces of metabolic waste ( urea, uric acid, ammonia)
– Lactic acid: chemical that attracts mosquitoes
– pH between 4-6
Sweat (Sudoriferous) Glands
Eccrine Sweat Glands
• Sweating is regulated by the sympathetic
nervous system
– Major role is to prevent overheating of the body
• Heat-induced sweating begins on the forehead and then
spreads inferiorly over the remainder of the body
• Emotionally induced sweating—so-called “cold sweat”
brought on by fright, embarrassment, or nervousness—
begins on the palms, soles, and axillae (armpits) and then
spreads to other body areas
Sweat (Sudoriferous) Glands
Apocrine Sweat Glands
• Largely confined to the axillary and
anogenital areas
• Larger than eccrine glands
• Ducts empty into hair follicles
• Secretion contains the same basic
components as true sweat, plus fatty
substances and proteins
– Quite viscous and milky or yellowish color
– Odorless:
• BUT, when its organic molecules are decomposed by
bacteria on the skin, it takes on a musky and generally
unpleasant odor (BODY ODOR)
Sweat (Sudoriferous) Glands
Apocrine Sweat Glands
• Little role in thermoregulation
• Role not completely understood
– BUT, they are activated by sympathetic nerve fibers
during pain and stress
• Because their activity is increased by sexual
foreplay, and they enlarge and recede with the
phases of a women’s menstrual cycle, they may
be analogous to the sexual scent glands of
other animals
Sweat (Sudoriferous) Glands
Ceruminous Glands
• Modified apocrine glands found in the
lining of the external ear canal
– Secrete a sticky, bitter substance called
cerumen, or earwax
• Thought to deter insects and block entry of
foreign material
Sweat (Sudoriferous) Glands
Mammary Glands
• Variety of modified sweat glands in the
breasts that secrete milk
Sebaceous (Oil) Glands
• Sebaceous glands are simple alveolar glands
(c) found all over the body except the palms of
the hands and soles of the feet
EXOCRINE GLANDS
Sebaceous (Oil) Glands
•
Secrete sebum, an oily
secretion:
– The central cells of the alveoli
accumulate oily lipids until they
become so engorged that they
burst, so functionally these
glands are holocrine glands
• The entire secretory cell
ruptures, releasing secretions
and dead cell fragments
• Secreting their product into a hair
follicle or to a pore on the surface
of the skin
– Sebum softens and lubricates
the hair and skin, prevents hair
from becoming brittle, and slows
water loss from the skin when the
external humidity is low
– Bactericidal action (bacteriumkilling)
Holocrine Gland
Sebaceous (Oil) Glands (a)
• Secretion is stimulated by hormones, especially
androgens
CUTANEOUS GLANDS
Sebaceous (Oil) Gland
HOMEOSTATIC IMBALANCE
• If a sebaceous gland duct is blocked by accumulated
sebum, a whitehead appears on the skin surface
– If the material oxidizes and dries, it darkens to form a
blackhead
• Acne is an active inflammation of the sebaceous
glands accompanied by “pimples” (pustules or cysts) on
the skin
– Usually caused by bacterial infection, particularly by
staphylococcus
• Seborrhea: cradle cap in infants
– Caused by overactive sebaceous glands
– Raised lesions that gradually become yellow to brown and begin
to slough off oily scales
Nails
•
•
•
•
A nail is a scalelike modification of the epidermis that forms a clear, protective
covering on the dorsal surface of the distal part of a finger or toe
Nails are made up of hard keratin
Each nail has a free edge, a body (visible attached portion), and a proximal root
(embedded in the skin)
The deeper layers of the epidermis extend beneath the nail as the nail bed
–
–
Corresponds to the superficial keratinized layers
The thicker proximal portion of the nail bed, called the nail matrix, is responsible for
nail growth
NAIL
Nails
• Nails normally appear pink because of the
rich bed of capillaries in the underlying
dermis
– Region that lies over the thick nail matrix appears
as a white crescent called the lunula (little moon)
• Proximal and lateral borders of the nail are
overlapped by skin folds, called nail folds
– Proximal nail fold projects onto the nail body as
the cuticle (eponychium=on the nail)
– Region beneath the free edge of the nail where dirt
and debris tend to accumulate is the hyponychium
(below nail), informally called the quick
Structure of a Hair
• Hairs, or pili, are flexible strands
produced by hair follicles that consist
largely of dead, keratinized cells
– The hard keratin that dominates hairs and
nails has two advantages over the soft
keratin found in typical epidermal cells:
• 1. It is tougher and more durable
• 2. Its individual cells do not flake off
Structure of a Hair
• The main regions of a hair are the shaft,
which projects from the skin, and the root,
the part embedded in the skin
HAIR SHAFT
HAIR
Structure of a Hair
• If the shaft is flat and ribbonlike in cross
section, the hair is kinky
• If the shaft is oval in cross section, the
hair is silky and wavy
• If the shaft is perfectly round in cross
section, the hair is straight and tends to
be coarse
Structure of a Hair
• A hair has three layers
of keratinized cells:
– Inner core (central core)
is the medulla
• Consist of large cells and
air spaces
• Absent in fine hair
– Middle layer is the cortex
• Bulky layer surrounding
the medulla, consists of
several layers of flattened
cells
– Outer layer is the cuticle
HAIR
Structure of a Hair
Cuticle
•
•
•
•
Formed from a single layer of cells
that overlap one another from
below like shingles on a roof
This arrangement helps to keep
neighboring hairs apart so that the
hair does not mat
– Hair conditioners smooth out the
rough surface of the cuticle and
make our hair look shiny
The most heavily keratinized part of
the hair, the cuticle, provides strength
and helps keep the inner layers tightly
compacted
It is subjected to the most abrasion,
the cuticle tends to wear away at the
tip of the hair shaft, allowing the
keratin fibrils in the cortex and medulla
to frizz out, creating “split ends”
HAIR SHAFT
Structure of a Hair
• Hair pigments (melanin of different colors) are made
by melanocytes at the base of the hair follicle and
transferred to the cortical cells
• Various proportions of melanins of different colors
(yellow, rust, brown, and black) combine to produce
hair color from blond to pitch black
– Red hair is colored by the iron-containing pigment called
trichosiderin
– Gray or white hair results from decreased melanin production
(mediated by delayed-action genes) and from the replacement
of melanin by air bubbles in the hair shaft (AIRHEAD-JOKE)
Structure of a Hair Follicle
• Hair follicles fold down from
the epidermis into the
dermis and occasionally into
the hypodermis
• The deep end of a hair follicle
is expanded, forming a hair
bulb, which is surrounded by
a knot of sensory nerve
endings called a hair follicle
receptor, or root hair plexus,
wraps around each hair bulb,
and bending the hair
stimulates these endings
– Consequently, our hairs act
as sensitive touch receptors
HAIR FOLLICLE
SKIN
Structure of a Hair Follicle
•
Hair papilla, a nipplelike bit of dermal tissue, protrudes into the hair bulb
– Contains a knot of capillaries that supplies nutrients to the growing hair
and signals it to grow
•
The wall of a hair follicle is composed of:
– Outer connective tissue root sheath, derived from the dermis,
– A thickened basement membrane called a glassy membrane,
– An inner epithelial root sheath, derived mainly from an invagination of the
epidermis
HAIR FOLLICLE
SKIN
Structure of a Hair Follicle
• Hair matrix: actively dividing
area of the hair bulb that
produces the hair
• Associated with each hair
follicle is a bundle of smooth
muscle cells called an arrector
pili muscle
– Most hair follicles approach
the skin surface at a slight
angle
– Arrector muscles are attached
in such a way that their
contraction pulls the hair
follicle into an upright
position and dimples the
skin surface to produce
goose bumps
SKIN
Types and Growth of Hair
• Hairs come in various sizes and shapes, but
can be classified as:
– Vellus: vell=wool, fleece
• Pale, fine body hair variety of children and adult females
– Terminal:
•
•
•
•
Darker
Coarser, longer hair of eyebrows and scalp
Axillary and pubic
Face and chest of males
• Hair growth and density are influenced by
many factors, such as nutrition and
hormones
Types and Growth of Hair
• The rate of hair growth varies from one body region to another and
with sex and age
– Averages 2.5 mm per week
• Life span of hairs varies and appears to be under control of a slew of
proteins
• Each follicle has a growth cycle where it is active and inactive for a
period of time
– Inactive, hair matrix cells die and the follicle base and hair bulb shrivel
– Follicle then enters a resting stage for a period of time
– After the resting phase, the matrix proliferates again and forms a new
hair to replace the old one that has fallen out or will be pushed out by
the new hair
– Only a small percentage of the hair follicles are shed at any one
time, we lose an average of 90 scalp hairs daily
– Follicles of the eyebrow hairs remain active for only 3-4 months, which
explains why your eyebrows are never as long as the hairs on your
head
HOMEOSTATIC IMBALANCE
• In women, small amounts of androgens
are normally produced by both the
ovaries and the adrenal glands
– Excessive hairiness (hirsutism: hirsut=hairy)
– Signs of masculinization
• Large amounts of androgens can be
secreted by ovarian tumors resulting in:
• Beard and hairy chest
– Tumors can be surgically removed
Hair Thinning and Baldness
• A follicle has only a limited number of cycles
in it
– Ideal conditions, hair grows faster from the teen years
to the 40s; then its growth slows
• The fact that hairs are not replaced as fast as they are shed
leads to hair thinning and some degree of baldness
(alopecia), in both sexes
– Begins at the anterior hairline and progresses posteriorly
– Coarse terminal hairs are replaced by vellus hairs, and the hair
becomes increasingly wispy
• Male pattern baldness, which is a type of true,
or frank, balding, is a genetically determined,
sex-influenced condition
FUNCTIONS
OF THE
INTEGUMENTARY SYSTEM
• Protection
– 1.Chemical barriers include skin
secretions and melanin:
• Although the skin’s surface teems with bacteria,
the low pH of skin secretions (acid mantle)
retards their multiplication
– Many bacteria are killed by bactericidal substances in
sebum
• Natural antibiotic (human defensin) kills bacteria
• Chemical pigment (melanin) prevents UV damage
FUNCTIONS
OF THE
INTEGUMENTARY SYSTEM
• 2.Physical or mechanical barriers are provided by the
continuity of the skin, and the hardness of the keratinized
cells
– Waterproofing glycolipids block diffusion of water and water
soluble substances between cells (preventing both loss and
entry)
• Lipid soluble substances DO penetrate:
–
–
–
–
–
Oxygen, carbon dioxide
Fat-soluble vitamins (A, D, E, K)
Steriods
Oleoresins (plants: poison ivy and oak)
Organic solvents (acetone, dry cleaning fluids, paint thinner)
» Causes kidney shut down and brain damage
– Salts of heavy metals (lead, mercury, nickel)
» Results in anemia and neurological defects
– Drug agents (penetration enhancers) that help ferry other drugs into the
body
FUNCTIONS
OF THE
INTEGUMENTARY SYSTEM
• 3.Biological barriers include:
– Langerhans’ cells of the epidermis
• Active elements of the immune system
• Respond to antigens
– Macrophages of the dermis
• Dispose of viruses and bacteria that have managed to
penetrate the epidermis
– DNA itself
• Absorb UV radiation and transfer it to the atomic nuclei,
which heat up and vibrate vigorously
– Heat dissipates to surrounding water molecules
instantaneously, the DNA converts potentially destructive
radiation into harmless heat
Body Temperature Regulation
• The skin plays an important role in body
temperature regulation by:
– Using the sweat glands of the skin to cool the
body:
• Evaporation of sweat from the skin surface dissipates body
heat and efficiently cools the body, thus preventing
overheating
– Constriction of dermal capillaries to prevent heat
loss:
• When the external environment is cold, dermal blood vessels
constrict causing the warm blood to bypass the skin
temporarily and allows the skin temperature to drop to that of
the external environment
– Passive heat loss from the body is slowed, thus conserving
body heat
Cutaneous Sensation
• Made possible by the placement of cutaneous sensory
receptors, which are part of the nervous system, in
the layers of the skin
• Cutaneous receptors are classified as exteroceptors
because they respond to stimuli arising outside the
body:
– Example:
• Meissner’s corpuscles (in dermal papillae) and Merkel dics allow
us to become aware of a caress or the feel of our clothing against
our skin
• Pacinian receptors (in deepest dermis and hypodermis) alert us to
bumps or contacts involving deep pressure
• Hair follicle receptors sense wind blowing through our hair and a
playful tug on a pigtail
• Bare nerve endings that meander throughout the skin sense
painful stimuli ( irritating chemical, extreme heat or cold, etc.)
Metabolic Functions
• When sunlight bombards the skin, modified cholesterol molecules
circulating through dermal blood vessels are converted to a
vitamin D precursor, and transported via the blood to other body
areas to play various roles in calcium metabolism
– Example: calcium cannot be absorbed from the digestive tract without
vitamin D
• Makes chemical conversions that supplement those of the
liver:
– Examples: keratinocyte enzymes can:
• 1. Disarm many cancer-causing chemicals that penetrate the epidermis
• 2. Convert some harmless chemicals into carcinogens
• 3. Activate some steroid hormones:
– Transform cortisone applied to the skin into hydrocortisone, a potent antiinflammatory drug
• Make several biologically important proteins, including
collagenase, an enzyme that aids the natural turnover of collagen
(deters wrinkles)
Blood Reservoir
• Dermal vascular supply is extensive:
– The skin may act as a blood reservoir by
holding up to 5% of the body’s blood supply,
which may be diverted to other areas of the
body should the need arise
• When other body organs, such as vigorously
working muscles, need a greater blood supply, the
nervous system constricts the dermal blood
vessels shunting more blood into the general
circulation, making it available to the muscles and
other body organs
Excretion
• Limited amounts of nitrogenous
containing wastes (ammonia, urea, and
uric acid) are eliminated from the body in
sweat, although most nitrogenous wastes
are excreted in urine
• Profuse sweating is an important
avenue for water and salt (sodium
chloride) loss
Skin Cancer
• Most tumors that arise in the skin are benign and do
not spread (metastasize) to other body areas
– Example:
• A wart: a neoplasm (abnormal growth of tissue that serves no
purpose but grows at the expense of healthy tissue) caused by a
virus
• Some tumors are malignant, or cancerous, and
invade other body areas
• A crucial risk factor for the nonmelanoma skin
cancers is overexposure to the UV radiation in
sunlight, which appears to disable a tumor suppressor
gene
– However, frequent irritation of the skin by infections, chemicals,
or physical trauma seems to be a predisposing factor
Skin Cancer
• Sunburned skin accelerates its production of
Fas, a protein that causes genetically damaged
skin cells to commit suicide, thus decreasing the
risk of mutations that will cause sun-linked skin
cancer
– It is the death of these gene-damaged cells that
causes the skin to peel after a sunburn
– NEW lotions are being produced that will fix damaged
DNA before the involved cells can develop into cancer
cells
• These lotions contain tiny oily vesicles (liposomes) filled
with enzymes that initiate repair of the DNA mutations
most commonly caused by sunlight
Skin Cancer
•
•
•
•
•
•
(a):Basal cell carcinoma is the
least malignant and the most
common skin cancer
Stratum basale cells proliferate,
invading the dermis and
hypodermis
Cancer lesions occur most often
on sun-exposed areas of the
face and appear as shiny, domeshaped nodules that later develop
a central ulcer with a pearly,
beaded edge
Relatively slow growing
Metastasis seldom occurs
before it is noticed
Full cure by surgical excision is
the rule in 99% of cases
SKIN CANCER
Skin Cancer
• (b):Squamous cell
carcinoma tends to grow
rapidly and metastasize if
not removed
• Arises from the
keratinocytes of the stratum
spinosum
• Lesion appears as a scaly
reddened papule (small,
rounded elevation) that arises
most often on the head (scalp,
ears, and lower lip), and hands
• If it is caught early and
removed surgically or by
radiation therapy, chance of
complete cure is good
SKIN CANCER
Skin Cancer
•
•
•
(c):Melanoma is the most
dangerous of the skin cancers
because it is highly metastatic and
resistant to chemotherapy
Cancer of the melanocytes
Begin wherever there is pigment:
–
–
–
•
Most appear spontaneously
About 1/3 develop from preexisting
moles
Usually appears as a spreading brown
to black patch that metastasizes rapidly
to surrounding lymph and blood
vessels
Key to surviving is early detection
–
–
Chance of survival is poor if the lesion
is over 4mm thick
Therapy is wide surgical excision
accompanied by immunotherapy
SKIN CANCER
Skin Cancer
• American Cancer Society suggests you regularly examine your
skin for new moles or pigmented spots and apply the ABCDE
rule for recognizing melanoma:
– A. Asymmetry:
• The two sides of the pigmented spot or mole do not match
– B. Border irregularity:
• The borders of the lesion exhibit indentations
– C. Color:
• The pigmented spot contains several colors (blacks, browns,
tans, and sometimes blues and reds)
– D. Diameter:
• The spot is larger than 6 mm in diameter (the size of a pencil
eraser)
– E. Elevation:
• Elevation above the skin
Burns
• A burn is tissue damage inflicted by intense
heat, electricity, radiation, or certain
chemicals, all of which denature cell proteins
and cause cell death to infected areas
• The most immediate threat to a burn patient
is dehydration and electrolyte imbalance due
to fluid loss
– Leads to renal shutdown and circulatory shock
(inadequate blood circulation due to reduced blood
volume)
– To save the patient, the lost fluids must be replaced
immediately
Burns
• The volume of fluid lost
can be estimated by
computing the
percentage of body
surface burned (extent of
the burns) using the rule
of nines (ONLY
APPROXIMATE)
– This method divides the
body into 11 areas, each
accounting for 9% of
total body area, plus an
additional area
surrounding the genitals
accounting for 1% of
body surface
BURNS
Burns
• Burn patients also need thousands of extra food
calories daily to replace lost proteins and allow
tissue repair:
– No one can eat this much, so burn patients are given
supplementary nutrients through gastric tubes and intravenous
(IV) lines
• After the first 24 hours has passed, the threat to a
burn patient becomes infection to the wound site:
– Burned skin is sterile for the first 24 hours
– Thereafter, bacteria, fungi, and other pathogens easily invade
areas where the skin barrier is destroyed, and they multiply
rapidly in the nutrient-rich environment of dead tissues
– Adding to this problem is the fact that the immune system
becomes deficient one to two days after severe burn injury
Burns
• Burns are classified according to their severity
– First-degree burns involve damage only to the epidermis
• Tend to heal in two to three days without special attention
• Sunburn is usually a first-degree burn
– Second-degree burns injure the epidermis and the upper region
of the dermis
• Blisters appear
• Skin regeneration occurs with little or no scarring within three to four
weeks if care is taken to prevent infection
– Third-degree burns involve the entire thickness of the skin
• Burned area appears gray-white, cherry red, or blackened, and
initially there is little or no edema (excessive tissue fluid-swelling)
• Since the nerve endings in the area have been destroyed, the
burned area is not painful
• Skin grafting is usually necessary
• Excessive scar tissue usually forms
Burns
• Burns are considered critical if any of the
following conditions exists:
– 1. Over 25% of the body has second-degree burns
– 2. Over 10% of the body has third degree burns
– 3. There are third-degree burns of the face, hands, or
feet
• Facial burns introduce the possibility of burned
respiratory passageways, which can swell and
cause suffocation
• Burns at joints are also troublesome because
scar tissue formation can severely limit joint
mobility
BURNS
ROSACEA
WINESTAIN
TATTO
DEVELOPMENTAL ASPECTS
OF THE
INTEGUMENTARY SYSTEM
• The epidermis develops from the embryonic ectoderm, and the
dermis and the hypodermis develop from the mesoderm
• By the end of the fourth month of development the skin is fairly well
formed
• During infancy and childhood, the skin thickens and more
subcutaneous fat is deposited
• During adolescence, the skin and hair become oilier as sebaceous
glands are activated
• The skin reaches its optimal appearance when we reach our 20s
and 30s; after that time the skin starts to show the effects of
cumulative environmental exposures
• As old age approaches, the rate of epidermal cell replacement slows
and the skin thins, becoming more prone to bruising and other types
of injuries