Skin Functions of Skin
► Mechanical/Chemical
damage – keratin
toughens cells; fats cells cushion blows; and
pressure receptors to measure possible
damage
► Bacterial damage – skin secretions are
acidic and inhibit bacteria.
► Ultraviolet radiation – melanin produced to
protect from UV damage
Skin Functions
► Thermal
control – regulates body temperature
 Heat loss: sweat to cool the skin
 Heat retention: prevents blood to rush into capillary beds
► Waterproofing
– contains lipids to prevent drying out
► Excretion of waste – urea and uric acid secreted in
sweat
► Makes vitamin D – modifies cholesterol molecules in
skin and converts it to vitamin D
Skin Structure
►Epidermis
— outer layer
 Stratified squamous epithelium
 Often keratinized (hardened by keratin)
►Dermis
 Dense connective tissue
►Subcutaneous
 hypodermis
tissue
Skin Structure
Summary of layers from
deepest to most superficial:
Stratum
Stratum
Stratum
Stratum
Stratum
basale
spinosum
granulosum
lucidum
corneum
Skin Structure
►Subcutaneous
tissue (hypodermis) is deep to dermis
 Not part of the skin
 Anchors skin to underlying organs, bones and muscles
 Contains half of the body’s fat; acts as padding and
insulation.
Layers of the Epidermis
►Stratum
basale
 Deepest layer of epidermis
 Cells actively undergoing cell division
 New cells are pushed upward to become the
more superficial layers
►Stratum
spinosum – intermediate layer
►Stratum granulosum – another layer
Layers of the Epidermis
►Stratum
lucidum
 Formed from dead cells of the deeper layers
 Occurs only in thick, hairless skin of the palms
of hands and soles of feet
►Stratum
corneum
 Outermost layer of epidermis
 Scale-like dead cells are filled with keratin
which is a protective protein preventing water
loss from skin
Keratinization
► Cells
migrate to the epidermis where eventually
they fall off.
► As they move upward, keratin is added.
► The cells in the epidermis contain a lot of keratin
which resists damage.
► Distinct layers of cells are called strata.
A cell takes ~ 40 – 56 from creation to sloughing off
Melanin
►Pigment
(melanin) produced by melanocytes
►Melanocytes are mostly in the stratum
basale
►Color is yellow to red to brown to black
►Amount of melanin produced depends upon
genetics and exposure to sunlight
Melanin continued….
►
►
►
Large amounts of melanin
occur in some regions like
freckles, moles, and
nipples.
Less melanin occurs in the
lips, hands, and soles of
the feet.
All races have the same
number of melanoctyes!
The amount of melanin
produced is determined by
genetics.
Albinism
►A
single mutation can cause a deficiency or
complete absence of melanin.
► Albinos have fair skin, white hairs, and
unpigmented eyes
Dermis
►Two
layers
 Papillary layer (upper dermal region)
►
Projections called dermal papillae
 Some contain capillary loops containing blood
 Some pain receptors and touch receptors
 Reticular layer (deepest skin layer)
►
►
►
Blood vessels
Sweat and oil glands
Deep pressure receptors
What causes Normal Skin Color
►Melanin
 Yellow, brown, or black pigments
►Carotene
 Orange-yellow pigment from some vegetables
►Hemoglobin
 Red coloring from blood cells in dermal
capillaries
 Oxygen content determines the extent of red
coloring
Dermis
►Overall
dermis structure
 Collagen and elastic fibers located throughout
the dermis
►
►
Collagen fibers give skin its toughness
Elastic fibers give skin elasticity
 Dermal papillae – extend toward the epidermis
and deliver nutrients, remove waste products
(sweat = urea and uric acid) and aid in
regulating body temperature.
What causes Normal Skin Color
►Melanin
 Yellow, brown, or black pigments
►Carotene
 Orange-yellow pigment from some vegetables
►Hemoglobin
 Red coloring from blood cells in dermal
capillaries
 Oxygen content determines the extent of red
coloring