The Integumentary System:
The Skin
Ch 4
The Basics
• Skin- The body’s
Cutaneous Membrane.
Also known as the
integument, meaning
simply “covering”.
• Integumentary SystemThis is the body’s organ
system made up of the
skin, sweat glands, oil
glands, hairs, and nails.
The Basic Functions of the Skin
• Basically a covering for the body.
• Keeps needed water and other precious
molecules in and keep unneeded water and
molecules out.
• Mainly used as protection from the
following damages:
Skin Functions:
Damages We are Protected From
• Mechanical Damage: Protected by Physical barrier, which
contains Keratin (toughens cells) and pressure sensors
(alerts nervous system to possible damage).
• Chemical Damage: Protected because skin has relatively
impermeable keratinized cells, which contain pain
receptors (alerts nervous system to possible damage).
• Bacterial Damage: Protected because skin has an unbroken
surface and “acid mantel” (skin secretions are acidic, thus
inhibit bacteria). Phagocytes ingest foreign substances and
pathogens, preventing them from penetrating into deeper
body tissue.
Skin Functions:
Damages We are Protected From (Con)
• Ultraviolet Radiation:
Protects because Melanin,
produced by the
melanocytes, offers
protection.
• Thermal Damage: Protects
because skin contains the
heat, the cold, and the pain
receptors.
• Dessication: Protects
because skin has
waterproofing keratin.
Skin Functions:
Other Functions
• Aids in heat loss/retention:
– Loss: Activates sweat glands and allows blood to flush
into skin capillary beds.
– Retention: By not allowing blood to flush into skin
capillary beds.
• Aids in Urea and Uric Acid Excretion: Contained in
perspiration produced by sweat glands.
• Synthesizes Vitamin D: Modified cholesterol molecules in
skin converted to vitamin D by sunlight.
Skin Structure: Basics
• Skin is made of two types of tissue.
– Epidermis: Outer layer made of stratified
squamous epithelium, capable of keratinizing,
or becoming hard and tough.
– Dermis: Lower layer made of dense connective
tissue.
Skin Structure: Basics (Con)
• Subcutaneous Tissue:
Deep to the dermis,
essentially adipose
tissue.
– Anchors skin to
underlying organs.
– Serves as shock absorber
and insulates deeper
tissues from extreme
temperature changes
occurring outside body.
Epidermis
• Avascular: Has no blood supply of its own.
• Deepest cell layer of Epidermis is Stratum
Germinativum.
– Lies closest to Dermis.
– Contains the only epidermal cells that adequate
nourishment.
• Cells are also constantly going through cell division.
• Millions of cells produced everyday.
Epidermis: Epidermal Cells
• Daughter cells move upward, to become part of
epidermal layers close to skin surface.
• Moves towards and become part of other layers:
– 1. Stratum Granulosum
– 2. Stratum Spinosum
– 3. Stratum Lucidum
• Once in Stratum Lucidum, they become flatter,
increasingly full of keratin, and finally die.
Epidermis (Con)
• Stratum Corneum: Outer-most layer, which is 20 to 30 cell
layers thick.
– Accounts for three-quarters of epidermal thickness.
– Has Cornified/Horny Cells, which are shingle-like dead
cell remnants, completely filled with Keratin.
• Keratin is exceptionally strong protein.
• Abundance in the Stratum Cerneum allows it to be a very
strong “overcoat” for the body.
• Protects cells from hostile environments and water loss.
• Layer rubs off slowly and steadily, and replaced by newly
made cells through cell division in lower layers.
• In reality, we get a totally new Epidermis every 35 to 45 days.
Epidermis (Con)
• Melanin: A skin pigment that ranges from yellow to brown
to black.
– Produced by special cells called Melanocytes.
– Found chiefly in Stratum Germinativum.
– When skin is exposed to sunlight, melanocytes are
stimulated to produce more melanin pigment, which is
what we call a tan.
– The layer’s cells phagocytize (eat) the pigment, and as
it accumulates within them, melanin forms protective
pigment “umbrella” over superficial, or “sunny” side of
their nuclei that shield their DNA from ultraviolet
damage from sunlight.
Epidermis (Con)
• Freckles and moles are
seen when Melanin is
concentrated in one
spot.
Epidermis (Con)
• Despite melanin’s damaging effects, too much
sunlight damages skin.
– Causes elastic fibers to clump, causing leathery
skin.
– Also depresses immune system.
– Overexposure to sun can also alter skin DNA
and cause Skin Cancer.
– Black people rarely have skin cancer, due to
their melanin’s amazing effectiveness as a
sunscreen.
Dermis
• Body’s “Hide”.
• Strong, stretchy envelope that holds the
body together.
• When buying leather goods, you are buying
the treated dermis of animals. Dense
connective tissue making dermis consists of
two layers:
– Papillary Layer
– Reticular Layer
Dermis (Con)
• Collagen fibers and elastic fibers are found
throughout the dermis layer.
– Collagen fibers responsible for toughness of
dermis.
– Also attract and bind water, thus helping to
keep skin hydrated.
– Elastic fibers give skin its elasticity when we
are young.
– As we age, number of collagen and elastic
fibers decrease, thus the skin wrinkles.
Dermis (Con)
• Dermis abundantly supplied with blood
vessels, which play a role in maintaining
body temperature homeostasis.
– When temperature high, capillaries of dermis
become engorged with heated blood and skin
becomes reddened and warm.
– When temperature cool, blood bypasses dermis
capillaries temporarily, allowing internal body
temperature to stay high.
Dermis (Con)
• Any restriction of
normal blood supply to
skin results in cells
death, sometimes
causing ulcers.
– Decubitus ulcers occur in
bedridden patients who
are not turned regularly
or who are dragged or
pulled across a bed
repeatedly.
The dermis consists of two major regions the
papillary layer and the reticular layer.
In depth Papillary Layer
The Papillary layer
is the upper dermal
region. The shape
is very uneven, it
looks like fingers
coming down from
the upper surface.
The fingerlike
projections are
called the dermal
papillae.
Blue Arrow=Papillary Layer
In depth…
The lower, reticular layer,
is thicker and made of
thick collagen fibers that
are arranged in parallel to
the surface of the skin. The
reticular layer is denser
than the papillary dermis,
and it strengthens the skin,
providing structure and
elasticity.
Red Arrow is the
Reticular Layer
Reticular Layer!!
Collagen and elastic fibers
(These are found throughout the dermis)
Collagen fibers
are responsible
for the toughness
of the dermis.
They also attract
and bind water,
and help to keep
the skin
hydrated.
Elastic fibers give the
skin its elasticity when
we are young. As we
age, the number of
collagen and elastic
fibers decreases, and
the subcutaneous
tissue loses fat. As a
result the skin becomes
less elastic and begins
to sag and wrinkle.
What do YOU produce?
Do you have brown-toned skin??
-This means you produce a lot of
melanin.Do you have lighter skin??
-This means that you have less melanin,
the crimson color of oxygen-rich
hemoglobin in the dermal blood
supply flushes through the
transparent cell layers above and
gives the skin a rosy glow. -
Redness or Erythema
Reddened skin may indicate
embarrassment, blushing, fever,
hypertension, inflammation, or allergy.
Skin Appendages…
The skin
appendages include
glands, hair, hair
follicles, and nails.
Each of these
appendages arises
from the epidermis
and plays a unique
role in maintaining
body homeostasis.
Words To Know…
A hair is produced by a
hair follicle. That part of
the hair enclosed in the
follicle is called the root.
The part projecting from
the surface of the skin is
called the shaft. A hair is
formed by a division of the
well-nourished cells in the
growth zone of the hair
bulb at the inferior end of
the follicle.
Hair Follicles…
• They are actually compound structures . Their
inner layer is composed of tissue and forms the
hair. The outer sheath is dermal tissue. The
dermal layer supplies blood vessels to the
epidermal portion and reinforces it.
• The erector pili is small bands of smooth muscle
cells. These connect each side of the hair follicle to
the dermal tissue.
Nails…
*scale like modification of the
epidermis that corresponds
to the hoof or claw of other
animals.
*Each nail has a free edge, a
body and a root.
*The borders of the nail are
overlapped by skin folds,
called nail folds.
*Nails are transparent and
nearly colorless, but they
look pink because of the rich
blood supply in the
underlying dermis.
*When the supply of blood is
low, the nail bed take on a
blue cast.
•Occurs on skin between toes
•Known as tinea pedis
•Results from a fungus called
Trichophyton
•Hair follicles and sebaceous glands infected
•Most common on the back of your neck
•Occur on areas with
sweat and friction
•Start as tender red bumps
•Become more painful and fill with pus
•When boils appear in clusters,
they become carbuncles
•Composite boils
•Caused by bacterial infection
•Those with diabetes, weaker immune
systems, or skin problems are more
likely to get them
•Fluid filled blisters
•Usually appear around lips and/or in tissues
that line mouth (oral mucosa)
•Activated by emotional upset,
fever, or UV radiation
•Itch and sting
•Common around mouth and nose area
•Water-filled lesions
•Skin is raised and pink
•Forms yellowish crust and
eventually ruptures
• Burns are classified by severity
• First degree
• Second degree
• Third degree
• First and second degree burns are
referred to as partial-thickness burns
• Third degree burns are referred to
as full-thickness burns
First Degree Burns
• Epidermis is only
damaged layer
• Not very serious
• Red, swollen skin
• Heal within 2-3
days
• Temporary
discomfort
• Example: sunburn
• Determines how
much of body
surface has been
burned
•Estimates volume
of lost fluid
• Skin is divided
into 11 areas
•Each area is
equal to 9 percent
of body surface
Types are:
• Basal Cell Carcinoma
• Squamous Cell Carcinoma
• Malignant Melanoma
Basal Cell Carcinoma
•Least malignant
•Most common
Sun-exposed areas of face
•Slow-growing
Malignant Melanoma
Only 5% of skin cancers
Often deadly
•Can begin wherever pigment exists
•Brown to black patches
• Used to recognize malignant melanoma
symmetry – two sides don’t match
order irregularity – borders aren’t smooth
olor – different colors
iameter – larger than 6 millimeters across