Download Cells of the Epidermis Keratinocytes

Chapter 5
The Integumentary
System
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Integumentary System
The largest system of the body
• Cutaneous membrane (SKIN)
• Outer epidermis (epithelial tissues)
• Inner dermis (connective tissues)
• Contents:
• Originate in the dermis extend
thru the epidermis to skin surface
• Hair, Nails, Multi-cellular exocrine glands
• Cardio vascular- Blood vessels in the
dermis
• Nervous - Sensory receptors for pain,
touch, and temperature
• Hypodermis (Superficial Fascia or Subcutaneous
Layer) NOT PART OF THE SKIN
• Loose connective tissue, below the dermis
• Location of hypodermic injections
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Integumentary System
FUNCTIONS of Skin
1. Protection
2.
3.
4.
5.
6.
• underlying tissues and organs from abrasions
• WBC in dermis…immunity
• Keratin…water proofing
• Production of melanin- skin color--protects from UV
Excretion of salts, water, and organic wastes (glands) using sweat
and sebum…protects from bacterial infections
• “Acid mantle”- pH of skin 4-6- reduces bacterial growth
Maintenance of body temperature (insulation and evaporation)
• Sweat…evaporates to cause cooling
• Blood vessels…vasoconstriction/vasodilation
• Arrector pili…goose bumps
Synthesis of vitamin D3
Storage of lipids
Detection of sensations: touch, pressure, pain, and temperature
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Epidermis
Avascular (no blood vessels) stratified
squamous epithelium
• Nutrients and oxygen diffuse from
capillaries in the dermis
Cells of the Epidermis
• Keratinocytes- most abundant
(90%)
• Contain large amounts of the
protein keratin
• Protects from heat, microbes,
and chemicals; releases a
waterproof sealant
• Water barrier forms
between the S. granulosum
and the S. spinosum –
crucial for retaining water
and preventing dehydration.
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Bound firmly to one
another with
numerous
desmosomes which
accounts for the
toughness of the
epidermis.
Epidermis
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• Thin Skin - Covers most of
the body (0.08mm “sandwich
bag”)
• Has four layers of
keratinocytes
1- Stratum basale
3- Stratum spinosum
4- Stratum granulosum
5- Stratum corneum
• Thick Skin -Covers the palms of the
hands and soles of the feet (0.5mm
standard paper towel)
• Has five layers of keratinocytes from
basal lamina to surface
1. Stratum basale (S. Basale)
2. Stratum spinosum (S. Spinosum)
3. Stratum granulosum (S.
Granulosum)
4. Stratum lucidum (S. Lucidum)
5. Stratum corneum (S. Corneum)
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Epidermis
STRATUM BASALE – Deepest and thinnest layer- thought to be a
single layer of cells
• Attached to basement membrane by hemi-desmosomes
• Produces a strong bond between epidermis and dermis
• Forms epidermal ridges (fingerprints)
• Dermal papillae (tiny mounds)
• Strengthens attachment between epidermis and dermis
• Area is actively dividing -has many basal cells or germinative cells
• Primarily comprised of basal keratinocyte cells, considered to be
the stem cells of the epidermis. Kerotinocytes in this layer do not
produce keratin. As new cells develop they are pushed
upwards. Eventually the cells will be little more than a plasma
membrane and keratin.
• Specialized Cells
• Merkel (tactile) cells- nerve cells (1%)-most sensitive skin w/o
hair- release chemicals that stimulate sensory nerve endings
• sense of light touch; discrimination of shapes and textures.
• Melanocytes (8%)
• Contain the pigment melanin scattered throughout S.basale
• Absorb damaging ultraviolet (UV) light
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Epidermis
STRATUM SPINOSUM —
consists of spiny prickle
cells; interlock to
support the skin
• When processed cells
shrink. Strength of
desmosomes create
pulling action
resembling miniature
“spiny” pincushions.
Not seen in living cells.
• Deeper layers continue to divide, increasing thickness of
epithelium; upper layers no longer participate in mitosis
• 99% of cells (8-10 layers bound by desmosomes) are
kerotinocytes produced by division of stratum basale- are prekeratin.
• Contain dendritic (Langerhans) cells (1%) derived from bone
marrow = White Blood Cells (WBC) participate in immune
response against pathogens that penetrate the skin
• Phagocytize melanin from melanocytes present in S basale
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Epidermis
Stratum Granulosum —
the “grainy layer”
• 3-5 keratinocytes
layers
• Cells stops dividing
begin producing
keratin, a tough,
fibrous protein found
in hair and nails
• As keratin fibers develop the cells grow thinner and flatter.
Membranes thicken and become impermeable
• Cells produce keratohyalin granules that dehydrate the cell;
nucleus and other organelles disintegrate and cell dies. This
creates a tightly interlocked layer of cells.
• Lamellated granules secrete glycolipids into the extracellular
space, form around the fibers and produce a water barrier.
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Epidermis
Stratum Lucidum — the “clear layer”
• Found only in thick skin - palms, feet soles
• protects against sun ultraviolet-ray damage
Stratum corneum the “horn layer”
• 15 to 30 layers of keratinized cells thick
• Top layer flat, dead cells- Packed with keratin
• Water resistant but not water proof; water from interstitial
fluids penetrate the surface and evaporate-insensible
perspiration
• S. Corneum continuously sheds and is replaced every 2 wks
• Dead cells call dander
• Dandruff –clumps of dander stuck together with sebum (oil)
• Keratinization - Formation of a layer of dead, cells filled with
keratin; Occurs on all exposed skin surfaces except the eyes
• Keratin protects the body from melanin and UV rays
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Cell Types and Layers of the of the
Epidermis
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Sweat pore
S. Corneum
Exfoliating
keratinocytes
S. Lucidum
Stratum granulosum
Dead keratinocytes
Sweat duct
Living keratinocytes
Dendritic cell
Stratum spinosum
Tactile cell
Melanocyte
Stem cell
Stratum basale
Dermal papilla
Tactile nerve fiber
Dermis
Dermal blood vessels
Figure 6.3
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PERSPIRATION
Epidermis
• Insensible perspiration- UNAWARE
• Interstitial fluid lost by evaporation through the stratum corneum
(500 ml/d)
• Cannot see or feel water loss
• If cells of the S corneum are damaged their effectiveness as a
water barrier is compromised. The superficial and deeper layers
of the epidermis are separated. Fluid accumulates between
producing blisters.
• Dehydration results:
• Severe damage to S. Corneum (serious burns) results in
excessive loss of interstitial fluid and life-threatening
circumstances
• Sensible perspiration -AWARE
• Water excreted by active sweat glands
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Skin Color
Influenced by Pigments
Carotene- Orange-yellow pigment
(found in fruits/vegetables)
• Can accumulate in epidermal cells
and fatty tissues of the dermis
• Can be converted to vitamin A
• Gives yellow hue to the palms, feet,
corns
Hemoglobin
• Network of blood capillaries varies
in dermis
• Gives reddish color to the skin
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Skin Color
Melanin - Yellow-brown or black pigment
• Approximately the same amount of
melanin in ALL skin
• Produced by melanocytes in stratum
basale
• Pigment phagocytized by
keratinocytes of upper layers of
epidermis
• Synthesized from amino acid
TYROSINE. The ENZYME
TYROSINASE converts tyrosine into
melanin.
• Melanin protects skin from sun damage
• Amount of pigment is controlled by:
• Genetics – amount of tyrosinase
• Melanin production, not number of melanocytes
• UV exposure - stimulates melanin synthesis (ie: tan)
• Causes DNA mutations and burns that lead to cancer and
wrinkles
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Clinical Applications of Skin Color
•
Pallor: temporary reduction of blood flow to the skin due to shock,
low BP, anemia
•
Cyanosis - bluish color in the nails and skin due to oxygen
circulation deficiencies
•
Jaundice - yellowish color to skin and whites of eyes due to the
buildup of yellow bilirubin in blood from liver/blood disease
•
Vitiligo: partial or complete loss of melanocytes  patchy skin
•
Erythema: redness of skin due to dilation of blood capillaries in
the dermis, caused by inflammation, infection, allergy or burns
•
Albinism: melanocytes are present but genetic condition fails
to produce tyrosinase necessary to synthesize melanin  no
color in the skin, hair and eyes
•
Freckles: area of skin where melanin is increased and
concentrated- no increase in melanocytes
•
Liver spots: INCREASE in melanocytes-unequal dispersal
•
Bruises: mass of clotted blood beneath the skin
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Cyanosis
Jaundice
Liver spots
Vitiligo
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Albinism
Skin Diseases
• Athlete's foot (also known as
ringworm of the foot) is a fungal
infection of the skin that causes
scaling, flaking, and itch of
affected areas, and in severe
cases, swelling and amputation of
the foot
• Oral herpes, colloquially called
cold sores or fever blisters, is an
infection of the face or mouth.
Most common form of infection.
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Vitamin D3
• Epidermal cells produce cholecalciferol
• In the presence of UV radiation
• Liver converts cholecalciferol to calcidiol
• Kidneys convert calcidiol into calcitriol
• Aids absorption of calcium and phosphorus
• Insufficient vitamin D3
• Can cause rickets in children
• Causes osteomalacia in adults
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Skin Cancer
1 million cases diagnosed per year
• three common forms of skin cancer
1. basal cell carcinoma (rarely metastasize) arises in epidermis
2. squamous cell carcinoma (may metastasize to lymph nodes)
• Good recovery with early detection
• Human papilloma virus associated with development
2. Squamous cell
1. Basal cell
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Skin Cancer
malignant melanomas (metastasize rapidly) ≤ 5% of cancers
arise from melanocytes
most common cancer in young women
Usually fatal-- 5-14% survival rate; causes the majority (75%)
of deaths related to skin cancer
• 6 months life expectancy following diagnosis
• Melanoma cells preprogrammed with ability to
metastasize. Unlike other cancer cells that must “learn”
how to travel and spread to other regions of the body.
• key to treatment is early detection watch
for changes in mole asymmetry, border,
color, diameter, evolving (“ABCDE”)
• risks factors include-- skin color, sun
exposure, family history, age and
immunological status
3.
•
•
•
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THE DERMIS
• Located between epidermis
and subcutaneous layer
• Connective tissue layer
• collagen & elastic fibers;
fibroblasts, macrophages
& fat cells
• Anchors epidermal accessory
structures nerves, (hair
follicles, nail roots, blood
vessels, glands)
Two major regions (zones)
• papillary region
• reticular region
• Consists of dense irregular connective tissue
• Contains larger blood vessels, lymphatic vessels, nerve fibers
and collagen and elastic fibers
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Skin – Dermis PAPILLARY region
• Lies directly beneath the epidermis and connects via finger-like
projections - dermal papillae
• Contains capillaries that nourish the epidermis
• Upper region of dermis comprised of areolar (loose) CT
• In hands and feet the papillae project into the epidermis and
forms contours in the skin's surface called friction ridges that
help to grasp by increasing friction. The ridges occur in patterns,
fingerprints, that are genetically determined and are therefore
unique to the individual
• All of the ridges of fingerprints form patterns called loops, whorls
or arches
• Each ridge contains pores, which are attached to sweat
glands under the skin which leave distinct patterns on
surfaces.
• Contains Meissner’s corpuscles (touch) & free nerve endings
for sensations of heat, cold, pain, tickle, and itch; hands, feet,
lips and genital organs; low nerve threshold (requires minimum
stimulation to register sensation); sensitive to light touching.
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Skin - Dermis
RETICULAR region:
• Dense irregular connective
tissue
• Lower region of dermis
• Has glands, hair follicles
and fat tissue
• Specific arrangement of
collagen fibers reflect on
the surface as cleavage
lines and wrinkle lines
on the surface
• Surgeons utilize these lines to improve healing time and
decrease scaring; A parallel cut remains shut, heals well; a
cut across (right angle) pulls open and scars
• Provides strength and elasticity to the skin; Resist force in a
specific direction
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Figure 5-8 Cleavage Lines of the Skin
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The Dermis- Clinical Applications
• Dermatitis - inflammation of the papillary layer
• Caused by infection, radiation, mechanical irritation, or chemicals
(poison ivy)
• Characterized by itch or pain
• Skin Damage
• Sagging and wrinkles (reduced skin elasticity) from
• Dehydration; Age; Hormonal changes; UV exposure
• Stretch marks
• Thickened tissue resulting from excessive stretching of skin
due to: pregnancy / weight gain
• Psoriasis: more rapid division of the stratum basale  thicker S
corneum  dry scales and flakes on the surface
• Callus and Corns: frequent friction on skin over a bone (manual
labor or tight shoes) increases keratinocytes replication resulting in
thicker S corneum  painful thickening
• Skin treatments such as cortisone easily move through the
epidermal layer of skin to reach the dermis. Cortisone is lipid based
(steroid) and can easily move through the phospholipid bilayer
plasma membrane of epidermal cells.
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Tattoos
• A tattoo is a form of body modification,
where a design is made by inserting
ink, dyes and pigments, either indelible
or temporary, into the dermis layer of
the skin to change the pigment.
• The presence of foreign material
activates the immune
system's phagocytes to engulf the
pigment particles. As healing proceeds,
the damaged epidermis flakes away as
the connective tissue dermal layer
mends and pigment is trapped
within fibroblasts.
• The word tattoo is a form of the
Polynesian word meaning “to write”.
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The Dermis
Dermal Strength and Elasticity
•
Presence of two types of fibers
1. Collagen fibers- very strong, resist stretching but bend
easily- provide flexibility
2. Elastic fibers -permit stretching and recoil
•
Skin turgor- water content of the skin helps to maintain the
properties of flexibility and resilience
Innervation (Nerves) of the Skin
• Nerve fibers in skin control:
• Blood flow
• Gland secretions
• Sensory receptors
• Light in dermal papillae
• Deep pressure and vibration—in reticular layer
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The Hypodermis;Subcutaneous; Superficial fascia
(NOT part of the Integumentary system!
• Lies below the epidermis and dermis
• Stabilizes the skin
• Allows separate movement
• Attaches skin to the underlying muscle layers
• Made of elastic areolar and adipose tissues
• Superficial area contains large arteries and veins; few capillaries
and no vital organs
• The site of subcutaneous injections using hypodermic
needles. Drugs injected into this area of the skin due to high
quantities of blood vessels and absorption capacity.
• Subcutaneous fat distributions result of hormones (leptin, insulin)
• Fat can be removed using liposuction which tears the adipose
tissue from the body
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Accessory Structures: HAIR
• Located in dermis
• Project through the skin surface
• 2.5 million hairs; 75% on general body surface and not the
head
• Body covered with hair, except:
• Palms; Soles; Lips; Portions of external genitalia
• Functions of Hair
• Protects and insulates
• Guards openings against particles and insects
• Sensitivity to very touch
• Types of Hair
• Vellus Hair: Soft, fine; covers body surface
• Terminal hairs: Heavy, pigmented
• Head, eyebrows, eyelashes, and pubic area
• Other parts of body after puberty
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Accessory Structures of Skin - Hair
Hair comprised of Soft keratin and Hard keratin
Hair parts: Shaft (visible) Root (imbedded)
Layers of the Hair- medulla, cortex & cuticle
Hair follicle = Jacket that surrounds hair root
• Base of the follicle
• Bulb
• Surrounded by touch sensitive nerves – hair root plexus
• Dermal papillae contains a knot of capillaries that supply
nutrients for hair growth
• Hair Matrix = Germinal cells in papilla for hair growth
Arrector pili:
• Smooth muscle band - attaches follicle to epidermis
• Contracts  goose bumps
Sebaceous glands lubricate the hair / control bacterial growth
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Structure of Hair and Follicle
three layers of the hair
• medulla
• flexible soft keratin- core of loosely
arranged cells and air spaces
• varies in thickness- Thick or coarse
hair usually contains a medulla.
• Fine hair for the most part lacks a
medulla, as does naturally blonde
hair.
• cortex
• constitutes the bulk of the hair;
hard keratin- hard stiffness
• cuticle
• multiple layers of very thin, scaly
cells that OVERLAP EACH
OTHER- hard keratin- free edges
directed upward. Accounts for split ends
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Hair Growth Cycle
Growth stage = Active growth stage of the hair fiber
•
can last from 2- 7 years. At any given moment 80-85% of our
hair is in this phase
Resting stage = hair growth begins to “shut down” and stop activity
•
cells accumulate keratin & follicle atrophies
•
Old hair (club hair) falls out and growth stage begins again;
new hair pushes the old hair out of the follicle
•
Normal hair loss is 70 to 100 hairs per day
Growth and replacement Influences
•
Cycle affected by illness, diet, high fever, surgery, blood loss,
severe emotional stress, and gender (hormones).
•
Chemotherapeutic agents affect the rapidly dividing matrix
hair cells resulting in hair loss.
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Hair Color
• Produced by melanocytes at the
hair papilla
• Determined by genes
Hair color depends upon amount
and type of melanin:
•
Dark hair – a lot of melanin
•
Red and blonde hair – different
type of melanin
•
Gray hair – decrease in melanin
production (decreasing
tyrosinase)
•
White hair – absence of melanin
and presence of air bubbles in
hair medulla; without melanin hair
is white as remaining hair
structures are transparent.
• Less melanin is produced as
one ages
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Sebaceous Glands and Sweat Glands
Exocrine Glands in Skin
•
•
Sebaceous Glands (oil glands)
• Holocrine glands; Secrete sebum
Sudoriferous “Sweat” Glands - Watery secretion
• Apocrine glands
• Merocrine (eccrine) glands
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Glands of the Skin – SEBACEOUS GLAND (Oil)
• Located in the dermis - 3-4 millions in adult skin
• Absent in the palms and soles
• Exocrine (holocrine) gland –cells are destroyed
• produce sebum - contains cholesterol, proteins, fats & salts
• Acinar glands accumulate lipids until engorged then burst
• secretions are stimulated by hormones at puberty
• Most sebum is secreted into hair follicles; exception: lips,
eyelids
• Function:
• moistens hairs
• waterproofs and softens /lubricates the skin
• inhibits growth of bacteria & fungi (ringworm)
Conditions:
• Cradle cap in infants
• Acne -- bacterial inflammation of glands
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sebacious
apocrine
Eccrine
merocrine
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Glands of the Skin -SUDORIFEROUS GLANDS
• Located in the dermis
• Duct opens on to the surface
of the skin
• Two types:
• heat induced
(merocrine)-moves via
ducts to surface of skin
• emotional (apocrine) –
open into hair follicle
• Function:
• regulates body
temperature through
evaporation (perspiration)
• help eliminate wastes
such as urea
http://sweatthroughit.com/wp-content/uploads/2014/01/sweat-gland.jpg
• Indicative of emotional or nervous responses
Sweat: protein-free filtrate of blood plasma (water), salts, urea,
lactic acid, ammonia….
• Released through exocytosis
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Merocrine (Eccrine)
sweat glands
1. Located all over the body, more
in the palm and soles
2.
Secretory portion is in dermis
with duct to surface
Apocrine sweat glands
(larger)
Limited in distribution to the skin of the
armpits, pubis, eyelids, ear canal, and
nipples
secretory portion in dermis ; duct opens
into hair follicle
3. Active right after birth
Active after puberty
4. Secretion is commonly referred to
Secretions are more viscous, sticky and
have a distinct odor. Source of
pheromones.
as “sweat”
5. regulate body temperature
Do not play a role in thermoregulation of
through evaporation (perspiration) the body
– prevents overheating; help
eliminate wastes such as urea,
Responds to hormonal and nervous
flushes microorganisms and
stimulus
other harmful chemicals
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Other Glands of the Skin
Ceruminous (wax) glands:
• Present in the skin lining the external canal of the ear
• Modified apocrine sudoriferous gland
• Secretes a waxy liquid (cerumen)
• Function: Protection against moisture and insect entry into the
ear canal
Mammary (milk) glands:
• Located between the pectoralis major
muscle and the skin
• Present in both male and female but only
function in females-action of gland is
triggered by pregnancy.
• Modified apocrine sudoriferous gland
• Secretes milk
• Function: Nutrition for the newborn
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Sebaceous Glands and Sweat Glands
Control of Glands
• Sebaceous and Apocrine sweat glands
• Autonomic nervous system (ANS)
• Works simultaneously over entire body
• Merocrine sweat glands
• Controlled independently
• Sweating occurs locally
• Thermoregulation
• Autonomic nervous system (ANS)
• Works with cardiovascular system
• Regulates body temperature
• The main function of sensible perspiration
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Nails
• Role: Protection - Made of thick, keratinized epidermis/hard keratin/
• Nail Plate is divided into:
• Nail body - visible part
• Nail root – embedded into the skin
• Nail growth: in the nail matrix surrounding the nail root
• Lunula: white region of the nail body…thickened stratum basale
• Eponychium (cuticle): S. corneum layer that projects over nail body
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Nails and Health
• Color
• Discolored: diabetes
• Bluish; asthma, heart condition, lung disorder
• Pale nails; asthma
• Yellowing: diabetes, liver issues
• Black streaks: heart
• White-reddish: folic acid, protein vitamin C Deficiency
• Shapes
• Curl under at tips: respiratory, heart
• White and thin: Vitamin B12 deficiency
• Vertical ridges: iron deficiency, poor nutrient/vitamin absorption
• Horizontal ridges: mental stress in some cases normal
• White spots: iron and zinc deficiency
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Repair of the Integument
1. Bleeding occurs due to dilated blood vessels
• Mast cells trigger inflammatory response
2. A clot-scab (network of fibrin) forms restoring the
integrity of the epidermis and restricting the entry of
microorganisms
• Germinative cells migrate around the wound
• Macrophages remove the remaining clot and
debris and deposit new collagen to replace it.
• Granulation tissue forms – a combination of
blood clot, fibroblasts, and blood vessels
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Tissue Injuries and Repair
Inflammation – first response; redness, swelling, heat, pain
• Triggered by trauma-injury, infection
• Damaged cells release chemical signals into the surrounding
interstitial fluid (Prostaglandins)
• As cells break down:
• Lysosomes release enzymes that destroy the injured cell and
attack surrounding tissues
• Tissue destruction is called necrosis
• Dead tissue and cellular debris (pus) accumulate in the
wound
• Can form abscess – pus trapped in an enclosed area
• Injury stimulates mast cells to release histamine, heparin,
prostaglandins
• Blood vessel dilate – bringing nutrients, O2, removing waste
• Results in redness, pain, warmth, swelling
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Tissue Injuries and Repair
• Regeneration
• When the injury or infection is cleaned up
• Healing (regeneration) begins
• Process:
• Fibroblasts/ Fibrocytes move into necrotic area
• Lay down collagen fibers to bind the area together (scar
tissue)
• New cells migrate into area
• Or are produced by mesenchymal stem cells
• The four tissue types vary in their ability to regenerate and repair.
• Epithelial and some connective tissue regenerate well
• Nervous tissue and cardiac regeneration poor or not at all
• Permanent replacement of normal tissue with scar tissue results
in fibrosis (scar tissue formation); structure and function are not
restored.
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Repair of the Integument
3. Epithelial cells multiply and spread beneath scab.
• Epithelium regenerates while the underlying connective
tissue undergoes fibrosis or scaring.
• Fibroblasts produce the scar tissue.
• Inflammation decreases, clot disintegrates
4. Scab sheds; Fibroblasts disappear
• Epidermis and blood vessel are restored to normal function
• A raised keloid (thick raised area of scar tissue) may form
Wound Healing animation
http://www.youtube.com/watch?v=IYL6vg89uds
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Keloid
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Burns
Caused by: Fire, electricity, radiations, and chemicals
Produces: Dehydration- most dangerous issue; lowered
body temperature, decreased blood pressure, decreased or
no urine production (kidneys shut down), infections
• First degree burn – epidermis is damaged  erythema,
pain, flaking and peeling
• Second degree burn – epidermis and part of the dermis
is damaged  erythema, blister formation, pain, partial loss
of skin functions and some scarring
• Blister –separation of the epidermis and dermis layers by a
fluid-filled pocket.
• Third degree burn – epidermis, dermis and accessories
lost  marble white area surrounded by redness, major
scarring
• Debridement: removal of dead skin (eschar) to prevent the
spread of infection
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Degrees of Burn Injuries
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Full-thickness burns
(a) First degree
1st degree
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(b) Second degree
2nd degree
(c) Third degree
3rd degree
Rule of Nines
Head
Trunk
Arms
Legs
Groin
9%
36%
18%
36%
1%
100%
Ex: burns that went into the
dermis and occurred over
entire surface of both arms
would be classified as:
• 2nd degree burn over 18%
of the body
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Burn Therapy
Skin Graft:
• Autograft – skin from one area to another area
of self
• Isograft – skin from an identical
twin…matching MHC antigens
• Homograft – temporary graft skin from another
person (donor, cadaver, foreskin)
• Heterograft – temporary grafts from another
animal (ie: pig, bovine)
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Effects of Aging on the Integumentary System
• Cells
• Epidermal thinning
• Decreased numbers of dendritic (Langerhans) cells
• Decreased melanocyte activity
• Activity
• Decreased glandular activity (sweat and oil glands)
• Decreased function of hair follicles
• Production
• Reduced blood supply
• Decreased vitamin D3 production
• Reduction of elastic fibers
• Decreased hormone levels
• Slower repair rate
© 2012 Pearson Education, Inc.