Download Integumentary System

Skin I
What are the functions of skin?
• “Keeps your insides in.”
• Protect deeper tissues from infection and some
toxins.
• Thermoregulation – control of body temperature.
• Sensory Input
• Synthesis of the active form of Vitamin D (the
“sunshine vitamin”) which maintains blood levels of
calcium and phosphorus
• Social and cosmetic implications
The three basic layers of skin
Epidermis
•Avascular
•No nerve supply
•Mainly stratified squamous epithelium
•Often keratinized for protection and
waterproofing
•Basement membrane border between
epidermis and dermis
Three general principles of epidermal growth
• Skin grows from the basal layer up.
• New cells are pushed up and begin to die.
Eventually they are shed and replaced by a
new generation of cells.
• Older cells form desmosomes and
undergo keratinization.
The 5 layers of epidermis (deep to superficial)
• stratum basale – deepest layer; source
of new cells. High mitotic rate.
• stratum spinosum – thick, “spiny” cells.
Large, central nuclei; beginning to flatten.
• stratum granulosum – 3-5 layers of
flattened cells; shriveled nuclei
The five layers of epidermis (deep to superficial)
• stratum lucidum – Cells appear clear
because they are dead and organelles
are breaking up.
• stratum corneum – tough, tightlypacked dead cells. Rich in keratin
protein.
Epidermal pegs
• Notice the ridges of
dermis as they form
waves into the
epidermis; these are
called dermal papillae,
or “pegs.”
Dermal pegs are responsible
for your fingerprints!
Dermis
• Vascular; good supply of blood
vessels
• Good nerve supply; painful if
damaged
• Mainly dense irregular connective
tissue – rich in collagen and elastin
fibers
The skeletal muscles of facial
expression anchor into the dermis.
Nerve cell processes are also located
in the dermis.
Pacinian corpuscles – heavy pressure
Meissner’s corpuscles – light pressure
Hypodermis
• Vascular; less blood supply than
dermis
• Rich in adipose tissue
• Anchors skin to deeper structures,
especially muscle
• No sharp boundary separating from
dermis
Hair Follicles
follicle = group of epidermal cells at
base of tube-like depression into the
dermis.
• Cell replication occurs at the base;
forming the root which is embedded
in the skin.
• Cells pushed up the shaft and
keratinize, forming the “hair.”
•
Electron micrograph – human hair
Smooth muscle
cells form
arrector pili. When
they contract the
follicle stands on
end
Piloerection in animals
Goosebumps!
Hair Color
• Hair color is genetic (polygenic, multiple
alleles)
• Darker hair – more melanin produced in
the cells
• Red hair has an iron-containing pigment
What causes
hair to be
naturally
straight or
curly?
Follicle Shape
Hair Loss
• Normally, hair goes through a resting phase
until a new one forms at the base of the
follicle, pushing the old one out.
• Sometimes the old
hair is not replaced
which can lead to
baldness
FINGERNAILS
Fingernails are keratin secretions produced
by epithelial tissue at the base of the nail.
Nails and Health
•
•
•
•
Blue bed – poor circulation
White bed or oval depression – anemia
Horizontal furrows – malnutrition
Extreme curvature – some lung/heart/liver
problems
• Red streaks – arthritis, ulcers, hypertension
Skin Glands
• Sebaceous glands secrete an oily substance
called sebum.
• This fatty, oily substance, helps to waterproof,
soften, and lubricate the skin and hair.
• Sebum is most often released by a sebaceous
gland at the base of a hair follicle, but some
regions have glands that release directly onto the
skin.
Skin Glands
• Sweat Glands originate deep in the dermis or
hypodermis, but are lined with epithelial cells
that secrete the sweat.
• Eccrine sweat glands open to a pore and function
to reduce body temperature.
• Apocrine sweat glands open into a hair follicle
and respond to physical and emotional stressors.
• These are responsible for the odor as their
secretions are metabolized by bacteria on
the skin
Skin Glands
• Other skin glands are modified sweat glands
–Ceruminous – secrete ear wax
–Mammary – secrete milk
Most of these glands release their
secretions via exocytosis
PIGMENTATION
Special cells in the
stratum basale,
called melanocytes,
secrete melanin.
The branches of the
melanocytes weave
through the
epidermis.
Melanin is released as the cells die. It accumulates
in the upper layers of skin.
More melanin accumulation creates darker skin.
Environmental factors
can darken existing
melanin and also
stimulate the
production of more
Well oxygenated blood can add a pinkish hue
Poorly oxygenated blood can cause blue skin –
called cyanosis
Constriction of blood vessels leads to paleness
And your skin really can turn
orange from eating too many
carrots due to pigment build-up
Some
variations
in human
skin tone
Albinism is a complete lack of
melanin production.
Skin color is
inherited on
multiple genes
with multiple
alleles leading to
the incredible
variety observed
in skin colors of
all people.
Injury
• Inflammation is a normal response to injury or
stress
• Blood vessels dilate to become more permeable
so fluids can more easily get to the damaged
tissue.
Healing from Cuts
• When skin is cut, the cells along the
margin are stimulated to divide more
• If the cut goes through the epithelial
layer and severs a blood vessel, you
bleed
• The clotting blood is
what forms the scab
• Phagocytic cells will remove the dead ones
• Suturing aids the healing process by
speeding the formation of new
collagenous fibers
Scars form when
the newly formed
connective tissue,
rather than
epithelium, is
seen at the
surface.
BURNS
Main problems associated with burns
• Infection – the protective skin barrier
has been compromised.
• Leakage and loss of water, electrolytes,
and protein, causing electrolyte
imbalance and protein deficiency.
• Psychosocial issues
Common types of burns
• 1st degree: only epidermis burned; pain,
redness, and swelling
• 2nd degree: “partial-thickness” epidermis
and dermis burned; pain, redness, swelling,
blisters
• 3rd degree: “full-thickness” epidermis and
dermis burned; damage to hypodermis and
fat has occurred. Skin often charred. May
or may not be pain initially
Rare types of burns
• 4th degree: burns into the underlying
muscle; motor damage likely
• 5th degree: all skin and subcutaneous tissue
destroyed, leaving muscle exposed;
amputation likely if survived
• 6th degree: exposes bone; almost always
fatal
The Rule of Nines
• The “rule of nines” is a way to
quantitatively estimate the damage done
to the body surface by burns. It is helpful
in making a prognosis for recovery and in
determining the extent of treatment.
The Rule of Nines
Body surface
Head
Percent
Face 4.5
Back of head 4.5
9%
Right arm
Anterior side
Dorsal side
4.5
4.5
9
Left arm
Anterior side
Dorsal side
4.5
4.5
9
Trunk – ventral surface
Chest
Abdomen
Trunk/back – dorsal surface
Upper back
Lower back
9
9
18
9
9
18
Right leg
Anterior Surface – 9
Dorsal surface – 9
18
Left leg
Anterior surface – 9
Dorsal surface – 9
18
Groin area
1
TOTAL SURFACE
100%
Rule of Nines
Treatment
• Skin grafts are often used for treatments of 3rd
degree burns. Donor skin is sutured over the
injured area.
– Autograft: from another part of own body
– Allograft: from another person
– Xenograft: from an animal (usually pig)
• Allo- and Xenografts are only temporary and
must be replaced by an autograft
Treatment
• Artificial skin is continuously researched
and scientists can now incorporate stem
cells into it for dermal growth.
• In the lab, atop of special membranes,
skin can grow from the size of a postage
stamp to the size of a poster in 3 weeks!