Seven Functions of Skin
►
►
►
Mechanical/Chemical
damage – keratin
toughens cells; fats cells
cushion blows; and
pressure receptors
measure damage
Bacterial damage – skin
secretions are acidic and
inhibit bacteria.
Ultraviolet radiation –
melanin produced to
protect from UV damage
Thermal control –
regulates body
temperature
 Heat loss: sweat to cool
the skin
 Heat retention:
prevents blood from
losing heat & shivering
Waterproofing – contains lipids to
prevent drying out
Excretion of waste – urea and uric acid
secreted in sweat
Makes vitamin D – changes cholesterol
molecules in skin and converts it to
vitamin D
Skin
— outer layer
►Dermis – middle layer
►Subcutaneous tissue – deepest layer
►Epidermis
 also referred to as the ‘hypodermis’
Structure
Epidermis
Summary of layers from
deepest to most superficial:
Stratum
Stratum
Stratum
Stratum
Stratum
basale
spinosum
granulosum
lucidum
corneum
A cell takes 40 – 56 days
from creation to
sloughing off
Layers of the Epidermis
►Stratum
basale
 Deepest layer of epidermis
 Cells actively undergoing cell division
 New cells push older cells upward until they
eventually fall off
 Cells are mostly keratinocytes and some melanocytes
Keratinization
► Keratin
is a protein that helps harden skin cells,
makes them tougher and helps prevent water
loss by the body.
Keratin makes the skin waterproof
► Keratinocytes are
responsible for
making keratin
Keratin is found in
cells of the basale
and spinosum
strata
► Stratum
spinosum –
Made of keratinocytes
 Some cells grow
projections that connect
to other cells making
the cell layer stronger
Prickle Cells with long projections
Stratum granulosum – mostly
flattened keratinocytes that
have lost nuclei and organelles
Death zone of keratinocytes
Vitamin D Production
► Cells
of stratum spinosum and basale:
 UV energy + cholesterol = Vitamin D
► Vitamin
D:
 used by kidney to make the hormone calcitriol
► Calcitriol:
 necessary to signal small intestine to absorb
calcium from the blood
► No
Vitamin D  no calcitriol 
no calcium absorption 
weak bones
► 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 strengthening
protein also preventing
water loss from skin
Layers of Skin
No Lucidum Layer
Melanin
► Pigment
(melanin) produced by
melanocytes
► Melanocytes are mostly in the
stratum basale
► Color is yellow to red to brown
to black
Melanocytes: Cells deep in the epidermis and
dermis that produce a pigment called melanin
which protects the cells from UV damage
Skin color determined by the
size and quantity of melanin
granules in the tissue
What’s your color?
►
Determined by genetic, environmental, and physiological
factors
 Your DNA determines how much MELANIN is produced
 UV radiation increases melanin production
 Circulation, vitamin deficiencies, physical ailments
(liver failure)
Why the Spots…?
► Large
amounts of
melanin occur in some
regions like freckles,
moles, and nipples.
► Caused by uneven
distribution of melanin
► Less melanin occurs in
the lips, hands, and
soles of the feet.
Albinism
►A
single gene mutation can cause a deficiency or
complete absence of melanin.
► Albinos have fair skin, white hairs, and
unpigmented eyes (eyes appear red)
Fingerprints
The up and down border between the
dermis and epidermis helps bond the
layers together
In thick skin, epidermal ridges show
on the surface as fingerprints:
Function – enhance gripping
Dermis – the middle layer
► Papillary
layer:
 Thin (20%)
 Consists:
► Contains
dermal papillae
► Capillaries, sensory neurons
 Function: feed epidermis
► Reticular
Layer:
 Thick (80%)
 Consists:
►Elastic
and Collagen fibers
► Sweat
and oil glands
► Deep pressure receptors
 Function: provide strength and flexibility
Dermal Papillae
► small,
nipple-like
extensions of the
dermis into the
epidermis
► Blood
vessels nourish
all hair follicles and
bring nutrients and
oxygen to the lower
layers of epidermal
cells
What makes us stay young looking?
►Elastic
fibers
 gives skin elasticity
 fibers can stretch up to 1.5x
their length and snap back
to their original length
when relaxed
►Collagen
fibers
 gives skin support/firmness
 ~ one quarter of the human body is collagen
 support the skin’s mechanical strength and texture
Sensory Perception in Skin
►
Skin is highly sensitivity to touch
because of large amounts of sensory
structures found in dermis
Sensory Perception
in Dermis
Merkel cells: deep layers of epidermis
- superficial touch
Free Nerve Endings: superficial dermis
- pain and temperature
Meissner’s Corpuscles: superficial dermis
- light touch
Pacinian Corpuscles: deep dermis
- pressure and vibrations
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.