protection (impact, abrasion, fluid loss, chemical attack), excretion (sweat), maintenance of body temperature (sweat, insulation), production of melanin, synthesis of Vitamin D3, storage of lipids, and detection (pressure, pain, touch, temp)
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epidermis is made of...
avascular stratified squamous epithelium
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how does the epidermis get nutrients?
O2 and nutrients diffuse from cells and fluid in the dermis (blood supply)
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where are more active cells in the epidermis?
close to the dermis
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what are the inactive or dead cells in the epidermis?
the superficial cells
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keratinocytes
an epidermal cell that produces and contains keratin
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keratinocytes gives strength to...
hair, skin, nails
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why do keratinocytes give skin a water-resistant quality?
to slow down dehydration
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thin skin
4 layers of keratinocytes, covers most of the body, thick as a plastic sandwich bag
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thick skin
5 layers of keratinocytes, on palms of hands and soles of feet, thick as a paper towel
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stratum basale
deepest layer of epidermis
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what does the stratum basale form?
epidermal ridges (example: fingerprints)
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what do the epidermal ridges in the stratum basale interlock with?
dermal papillae (creates a strong bond when interlocked)
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cells in the straum basale
germinative cells and merkel cells
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germinative cells
stem cells in the stratum basale that can divide to replace lost epidermal cells
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merkel cells
sensory cells in the stratum basale that respond to touch
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where are melanocytes located?
stratum basale
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stratum spinosum
second deepest layer of epidermis
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where do daughter cells from germinative cells get pushed to?
stratum spinosum
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stratum spinosum cells...
are alive and continue dividing
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Langerhans cells
a type of dendritic cell (white blood cell) found in the stratum spinosum that can activate on immune response if bacteria invade
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stratum granulosum
middle layer of the epidermis
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What occurs in the stratum granulosum?
keratinocytes stop dividing and start producing lots of keratin
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stratum lucidum
fourth deepest layer in the epidermis, "missing layer" in thin skin
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what are the cells like in the stratum lucidum?
flattened, densely packed and filled with keratin
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stratum corneum
outermost layer of epidermis
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what is the water-resistant layer of the epidermis?
stratum corneum
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stratum corneum consists of...
15-30 layers of dead, keratinized cells, tightly interconnected by desmosomes
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stratum corneum is described a the \______.
horn layer
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what does the stratum corneum cover?
all exposed surfaces except eyeballs
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keratinization
the formation of a layer of dead, protective cells filled with keratin
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how many days for a cell to move from the stratum basale to the stratum corneum?
15-30 days
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how long can cells stay in the stratum corneum before falling off and joining the dust?
up to 2 weeks
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as the layers get closer and closer to the surface, what happens to the cells?
less active, flatter, more filled with keratin, dead
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types of perspiration
insensible and sensible
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insensible perspiration
interstitial fluid lost by evaporation through the stratum corneum, lose up to 500 mL of H2O per day by evaporation, includes water vapor you exhale
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sensible perspiration
water excreted by sweat glands
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wrinkly skin in water
occurs due to osmosis
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what type of solution will cause wrinkly skin?
hypotonic solution (fresh water)
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how does wrinkly skin in water occur?
water diffuses into the dead, flat, keratinocytes of the stratum corneum so they swell up to 4x the normal volume, noticeable in thick skin
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basis of skin color
result of epidermal pigmentation and dermal circulation
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epidermal pigments
carotene and melanin
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carotene
yellow-orange pigment found in plants
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where does carotene accumulate?
epidermal cells and fatty tissues
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what can carotene be converted to?
Vitamin A
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melanin
dark-brown or yellow-brown pigment produced by melanocytes in the stratum basale
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number of melanocytes in darker vs light people
same number
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how does melanin travel?
pigment molecules travel upwards from the stratum basale and enter into the keratinocytes
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why do some people have darker skin?
melanin travels more toward the surface in darker skinned individuals
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why do people have freckles?
overproduction of melanin
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function of melanin
protects skin from sun damage by absorbing UV radiation
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why do we need melanin to absorb UV radiation?
it causes DNA mutations and premature aging of skin
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why does tanning occur?
increasing melanin protection for UV protection
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what happens when melanin enters keratinocytes?
it specifically clusters around the cell nuclei
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role of dermal circulation
redness
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what happens if blood flow decreases to skin?
skin pales
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why do old people look pale?
less melanin production, blood flow to the dermis decreases with age
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cyanosis
a bluish skin tint caused by severe reduction in blood flow or lack of oxygen
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jaundice
skin and whites of the eyes turn yellowish due to liver problems
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why do people turn yellow due to liver problems?
if the liver cannot make bile, a yellowish pigment accumulates in body fluids
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bile
a substance that helps break down fats in the digestive tract
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why are babies sometimes born with jaundice? how long does it take to resolve itself?
their liver is not fully developed, resolves itself in 2-3 weeks
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vitiligo
autoimmune disorder where there are patches of skin with no melanocytes
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what percent of people have vitiligo?
1%, but is more noticeable in darker skin
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is vitiligo dangerous?
no, it is mostly a cosmetic problem
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how is vitamin D3 produced?
cells in the stratum spinosum and stratum basale produce vitamin D3 when exposed to UV rays
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what does the "3" mean in vitamin D3?
3 is the form the body needs and makes
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what vitamin comes from plants and in converted to D3 in the body?
vitamin D2
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what do the kidneys convert vitamin D3 into?
calcitirol, a hormone essential for calcium absorption
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vitamin D3 is needed to absorb calcium from \__________ into \__________.
the intestine, the blood
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rickets
vitamin D3 deficiency
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where is rickets most often seen?
in children living in extreme poverty
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what does rickets result in?
weak, flexible bones with abnormal bone development
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what anchors accessory structures?
the dermis
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2 layers in the dermis
papillary layer and reticular layer
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papillary layer
outer layer of the dermis, directly beneath the epidermis (adjacent to the stratum basale), name for the dermal papillae
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what is the papillary layer made of?
areolar tissue
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reticular layer
deeper layer of the dermis that supplies the skin with oxygen and nutrients
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what is the reticular layer made of?
dense irregular connective tissue with collagen and elastin fibers and various cells found in the connective tissue proper
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can the reticular layer stretch?
a bit, but the collagen protects it from stretching too much
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papillary layer vs. reticular layer
capillaries, smaller lymphatics and nerve ending vs. longer blood vessels, lymphatics, and nerves
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stretch marks
caused by tearing or rupturing collagen and elastic fiber bundles in the dermis
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cleavage lines
bundles of collagen and elastic fibers in the dermis
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why are cleavage lines useful for surgery?
A cut parallel to, or between the bundles heals well with minimal scarring, but a cut through a bundle leads to more difficult healing and greater scarring
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contusion
(bruise) damaged blood vessels bleed blood into the dermis
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what color appearance do contusions have?
black and blue
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why do contusions turn yellowish-green?
as the hemoglobin in the trapped blood gets broken down, the bruise fades and a green pigment and yellow pigment get made (same yellow pigment that builds up in jaundice)
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Flashcard (67)