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Skin and the Integumentary
System
Chapter 6
What exactly is skin?
• It is an organ composed of several kinds of tissues
• Largest organ
• Performs many functions
– Maintains Homeostasis
– Prevents harmful substances such as chemicals and
microorganisms from entering body
– Prevents water loss
– Maintains temperature
– Houses sensory receptors
– Contains immune cells
– Produces chemicals such as Vitamin D
– Excretes wastes
Two main layers and one below*
1. Epidermis
- Outer layer
- Composed of stratified squamous epithelium
2. Dermis
-
Inner layer
Thicker than epidermis
Made up of connective tissue, smooth muscle tissue,
nervous tissue, blood, and other types of epithelial tissue
(glands for example)
*Beneath the dermis is the subcutaneous layer
The epidermis and dermis are separated by the
basement membrane that the stratified squamous
epithelium is attached to
EPIDERMIS
• Lacks blood vessels
• Made up of 4 or 5 layers
– Stratum Basale (closest to basement membrane)
– Stratum Spinosum
– Stratum Granulosum
– Stratum Lucidum (Optional)
– Stratum Corneum
As each layer gets pushed upward, the cells
change their shape and become more
squamous or flattened.
Stratum Basale
• The deepest layer – the contains cells that are
actively dividing
– Attached to the basement membrane
– They are closest to the dermis, which contains
blood vessels, so they receive nutrients and O2
– As they divide, they push the older cells toward the
top. Cell division prevents wear and tear – the
more the use of the body part, the more the cell
division (calluses, corns, etc.)
– Specialized cells in this layer called melanocytes,
produce melanin, which provides skin color
Stratum Basale
Stratum Spinosum
• A thick layer of squamous epithelial cells right
above the stratum basale
Stratum Spinosum
Stratum Granulosum
• A granular layer of squamous epithelium
above the stratum spinosum
Stratum Granulosum
Stratum Lucidum
• An optional layer of squamous epithelium – only found
in thick skin
• Found in palms of hand or soles of feet
Stratum Lucidum
Stratum Corneum
– Topmost layer of squamous epithelium. Flatten cells
– These cells are called Keratinocytes, because their
cell membranes thicken with a protein called
keratin.
– This hardens them, makes them waterproof.
– The farther the keratinocytes travel from the stratum
basale, the less nutrients they have, so they
eventually die.
– The older keratinocytes develop many
desmosomes
– The tough sheet of dead cells is called the Stratum
Corneum and is shed (exfoliation)
Stratum Corneum
Layers of the Epidermis
Melanocytes
Melanocytes and Melanin
• Although melanocytes are found in the
stratum basale, their product – melanin
can be found in other cells of the
epidermis and sometimes even in the cells
of the connective tissue underneath
• This is because the melanocytes transfer
the melanin to the neighboring cells via
cellular extensions called dendrites – this
process is called cytocrine secretion
More about Melanin
• Melanin absorbs UV radiation – prevents skin cancer
• Skin color depends mainly on the amount of the brown pigment
melanin produced in the skin.
• All people have about the same number of melanocytes.
However, the melanocytes of dark-skinned people produce
more melanin than do those of light-skinned people. The
amount of melanin produced in each person's skin is
determined mainly by heredity.
• Exposure to sunlight increases the production of melanin,
causing light skin to tan. In some cases, melanin builds up in
small spots, forming freckles.
• As someone grows older, the melanocytes produce melanin at
uneven rates, which causes some areas of the skin to remain
light and others to darken. These dark spots are sometimes
called age spots or liver spots.
Cytocrine Secretion
Sunburn (Solar Erythema)
•Too much UV radiation
•Epidermal cells become “sick”
•Skin becomes red, swollen
and painful
•Cell undergo Apoptosis or
programmed cell death
•Apoptosis kills damaged cells
to prevent skin cancer
•Stratum basale will replace
lost cells
Skin Cancer
• Over exposure to UV light and
other genetic and environmental
conditions will cause skin cancer
• Thymine dimers (T-T) form in the
DNA of DNA repair enzyme
genes
• So DNA damage, misspellings
cannot be proof-read or repaired
• Mutations develop, leading to
cancer
• This occurs in a rare genetic
disorder called Xeroderma
pigmentosum
The Dermis
• Below epidermis
• Boundary between epidermis
and dermis is uneven due to
dermal papillae that extend
into ridges in the epidermis
• This creates ridges and
fingerprints on the palm of the
hand and fingers
• Fingerprints are unique and
genetically determined
Dermis, cont’d.
• Two types of nerve receptors in the dermis:
1. Pacinian corpuscles: stimulated by heavy touch or pressure
2. Meissner’s corpuscles: stimulated by light touch
• Made up of irregular dense connective tissue containing
collagen and elastic fibers
• Contains smooth muscle, blood vessels, nerve tissue,
hair follicles, sweat glands, and sebaceous glands.
Full-thickness Skin
Subcutaneous Layer
• Below dermis
• Composed of loose connective tissue
• No clear boundary between dermis and
hypodermis
• Contains adipose tissue layer for
insulation
• Contains major blood vessels that form a
network called the Rete cutaneum – these
send smaller extensions into the dermis
Subcutaneous Layer - Hypodermis
Accessory Organs of the Skin
• Hair follicles
• Nails
• Skin glands
– Sebaceous glands
– Sweat glands (a.k.a sudoriferous glands)
• Eccrine
• Apocrine
Hair Follicles
• Follicles are present on all skin excepts palms,
soles, lips, nipples
• In some areas that grow hair, the hair may be
fine, while in others it may be thick
• A hair grows out of a deep tube that extends
from the surface of the skin, all the way into the
dermal layer – this is a follicle
• Each hair follicle is also connected to sebaceous
glands that produce oils and other secretions
Hair Follicle, cont’d.
• The follicle contains the growing hair
• The base of the hair is composed of
actively dividing epidermal cells
• These epidermal cells are nourished by
dermal blood vessels that project into
connective tissue that then project into the
hair base – this vascularized connective
tissue projection is called the hair papilla
Hair Growth
• As the epidermal cells divide,
they push older cells upward
through the follicle
• As the older cells move away
from the nutrient supply, they
become keratinized and die
• These dead keratinized
epidermal cells are what make
up a strand of hair
• Hair color is genetically
determined and is pigmented
by melanocytes - the more
the melanin in the dead
epidermal cells, the darker the
hair
A strand of hair has
three layers:
cuticle, cortex, and
medulla.
The outermost
covering, cuticle
consists of hard
overlapping protein
scales that point toward
tips end. The cortex
contains pigment
granules that give hair
its color. The medulla is
a hollow tube within the
hair, which may be
present or
absent. Depending on
the hair, this hollow tube
is continuous, or
fragmented.
Hair Color
• White – lacks melanin (albinism)
• Gray hair – a mix of pigmented and
unpigmented hair
• Black and brown – tons of melanin
• Blonds – Less melanin
• Red hair – contains an extra pigment
called trichosiderin (iron based)
Goosebumps!
• Smooth muscle attached to each hair follicle can
contract and cause short hairs to stand on end
• These muscle bundles are called arrector pili
muscles
• They appear when scared, excited, cold, etc.
Nails
• Evolved to protect the tips of
fingers and toes
• Consists of:
– Nail plate (the actual nail)
– Nail bed (skin surface on
which the nail plate sits)
• Nail plates are synthesized by
special epithelial cells at the
base of the nail – a region called
a Lunula (half moon shaped)
• As epithelial cells divide, they
become keratinized, hard and
scaly, and get pushed over the
nail bed
Good Nails, Bad Nails
Psoriasis of the nails
Nail Biting
Glands - Sebaceous
• Holocrine glands
• Usually associated with hair follicles
• Specialized epithelial cells in this gland produce
a fatty secretion that accumulates and bursts
through cells
• The final product is a mix of cell debris and fatty
fluid – this is called Sebum
• Sebum is secreted into hair follicles
• Keeps skin and hair soft, flexible and waterproof
• Too much sebum causes pores to clog and
results in acne
Acne
Glands - Sweat
1. Eccrine sweat glands
– Most numerous on body
– Eccrine ducts are independent of hair
follicles
– Respond to heat – secrete sweat to cool
body
– Fluid is mostly water, salt, urea and uric acid
– Reaches surface of skin through a pore
Eccrine Sweat Glands
Glands - Sweat
2. Apocrine sweat glands
–
–
–
–
–
Only found in armpits, groin, nipples
Apocrine ducts open into hair follicles
Become active during puberty
Secrete when excited, upset, anxious, etc.
Apocrine sweat is also basically water and
salts, but also contains sebum and other fats
that bacteria love and metabolize – this
creates the bad odor in arm pits, etc.
Apocrine Sweat Glands
Temperature Regulation
• Humans (Mammals) are homeotherms (
warm-blooded). This means we maintain
a fairly constant body temperature
• We do this mainly by adjusting our rate of
cellular respiration and by using organs
such as the skin to warm and cool us
down
Heat loss is caused by:
• Radiation – heat from body radiates to cooler
surroundings
• Conduction – heat from body transfers directly
to a cooler surface (your rear end warms your
seat, so it feels warm to the touch)
• Convection – heat from the body escapes to
cooler air around the body
• Evaporation – when sweat evaporates, it
takes body heat away with it, cooling the body
Heat Loss, cont’d.
In cold weather, blood vessels
constrict, so that heat is
retained in the body.
In hot weather, blood vessels
dilate, so heat is lost by
convection and radiation
Evaporative cooling
As water molecules evaporate,
they carry some of the heat with
them, thus cooling the surface
they leave behind
Hyperthermia
• Normal body temp – 37C or 98.6F
• Body temperature can get elevated during hot
days and physical exercise
• Body also elevates temperature (fever) to fight
infection, because some bacterial and viral
enzymes are denatured at above normal
temperatures
• But extremely high fevers can cause:
– Dehydration and loss of electrolytes
– the body’s own enzymes and proteins to denature and
lead to death
Cool it!
• Body temperature is
reduced by sweating,
staying in a cool
environment and slowing
physical activity
• Drinking plenty of fluids
• Fevers can be reduced
by taking ibuprofen and
acetaminophen
Hypothermia
• Caused by over
exposure to cold
temperatures
• Starts with
shivering, followed
by mental
confusion,
numbness,
lethargy, loss of
consciousness and
eventually death
Accidents
• Cuts
• Burns
Clots
When an injury such as a cut occurs,
platelets become activated platelets.
They change their shape, become
sticky and build up on a blood vessel
wall to form a plug. Platelets are also
involved in the secretion of chemical
platelet factors into the blood plasma.
In a complex series of reactions
fibrinogen is converted into fibrin, an
insoluble protein that forms an
intricate network of tiny threads
called fibrils. Blood cells and plasma
are tangled in the network of fibrils to
form the clot.
Clotting and Healing
Scars
• If a cut is deep into
the dermis, new
connective tissue
develops in the
normal epidermis
• This new “skin” lacks
hair follicles, sweat
glands, and other
components of
normal skin
Burns
Burn injuries can be classified as thermal (heat), chemical, or
electrical.
• Thermal (heat) burns. Not all thermal burns are caused by
flames. Contact with hot objects, flammable vapor that ignites
and causes a flash or an explosion, and steam or hot liquid are
other common causes of burns.
• Chemical burns. A wide range of chemical agents can cause
tissue damage and death if they come in contact with the skin.
As with thermal burns, the amount of tissue damage depends
on the duration of contact, the skin thickness in the area of
exposure, and the strength of the chemical agent. Chemicals
will continue to cause tissue destruction until the chemical
agent is removed. Three types of chemicals-acids, alkalis, and
organic compounds-are responsible for most chemical burns.
• Electrical burns. The severity of an injury from contact with
electrical current depends on the type of current (direct or
alternating), the voltage, the area of the body exposed, and the
duration of contact.
Burn Assessment
For assessment purposes, the
body is divided into regions
representing 9% (or a multiple
of 9)
Three degrees of burns
• First-degree burns are usually limited to redness (erythema),
a white plaque and minor pain at the site of injury. These burns
usually extend only into the epidermis.
• Second-degree burns additionally fill with clear fluid, have
superficial blistering of the skin, and can involve more or less
pain depending on the level of nerve involvement. Seconddegree burns involve the superficial (papillary) dermis and may
also involve the deep (reticular) dermis layer.
• Third-degree burns additionally have charring of the skin, and
produce hard, leather-like eschars. An eschar is a scab that has
separated from the unaffected part of the body. Frequently,
there is also purple fluid. These types of burns are often
painless (insensate) because nerve endings have been
destroyed in the involved areas.
Aging
•
•
•
•
Dermis slows down synthesis of collagen and elastin
Fat is lost from subcutaneous layer, so wrinkles appear
Hair follicles reduce in number, hair growth slows or stops
Blood supply to skin, hair and nails is reduced, so nails
change texture, become brittle
• Loss of nerve tissue in skin makes less sensitive to
environmental stimuli
• Reduced blood supply makes an older person more
susceptible to hypothermia
Young skin vs. Old
Skin Diseases/Rashes
•
•
•
•
•
•
•
•
•
Chickenpox
Shingles
Herpes
Smallpox
Fifth Disease
Impetigo
Lyme Disease
Scarlet Fever
Psoriasis
Chickenpox
• Caused by the varicellazoster virus. It is
characterized by fever and
an itchy and blistered rash. It
is a highly contagious
disease. Although
chickenpox-related
complications are relatively
rare among healthy children,
the disease could be more
dangerous among infants
and the older age groups.
Shingles
• The varicella-zoster virus
remains latent or
dormant in the body and
can later be reactivated
and cause shingles
(herpes zoster). This
new version is NOT
contagious.
Herpes
• The herpes simplex virus can
cause oral or genital herpes
• There are two types of
Herpes Simplex Virus. Both
types can cause genital
herpes and oral herpes. HSV
type 1 usually infects the lips.
• Herpes Simplex Virus type 2
is the usual cause of genital
herpes. However, it also can
infect the mouth during oral
sex.
Smallpox
• Smallpox (also known by the
Latin names Variola or Variola
vera) was a highly contagious
viral disease unique to humans.
It is caused by two virus variants
called Variola major and Variola
minor. V. major is the more
deadly form, with a typical
mortality of 20–40 percent of
those infected. The other type, V.
minor, only kills 1% of its victims.
Many survivors are left blind in
one or both eyes from corneal
ulcerations, and persistent skin
scarring—pockmarks—is nearly
universal.
Fifth Disease (human parvovirus B19)
• Fifth disease is a mild rash
illness that occurs most
commonly in children. The ill
child typically has a "slappedcheek" rash on the face and a
lacy red rash on the trunk and
limbs. Occasionally, the rash
may itch. An ill child may have
a low-grade fever, malaise, or
a "cold" a few days before the
rash breaks out. The child is
usually not very ill, and the
rash resolves in 7 to 10 days.
Impetigo
• Impetigo, a contagious skin infection that usually
produces blisters or sores on the face and hands, is one
of the most common skin infections among kids.
• It is generally caused by one of two bacteria: group A
streptococcus or staphylococcus aureus. Impetigo
usually affects preschool and school-age children,
especially in the summer months.
Scarlet fever
• Caused by an infection with
group A streptococcus
bacteria. The bacteria make a
toxin (poison) that can cause
the scarlet-colored rash from
which this illness gets its
name.
Lyme Disease
• Lyme disease is caused by the
bacterium Borellia burgdorferii
and is transmitted to humans by
the bite of infected blacklegged
ticks. Typical symptms include
fever, headache, fatigue, and a
characteristic skin rash called
erythema migrans. Most cases
of Lyme disease can be treated
successfully with a few weeks
of antibiotics. If left untreated,
infection can spread to joints,
the heart, and the nervous
system.
Typical “bull’s eye” rash
THE END