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layerlayer also referred to as the ‘also referred to as the ‘hypodermishypodermis’’
EpidermisEpidermis
Summary of layers from Summary of layers from deepest to most deepest to most superficial:superficial:
Stratum basaleStratum basale Stratum spinosumStratum spinosum Stratum Stratum granulosumgranulosum Stratum lucidum Stratum lucidum Stratum corneumStratum corneumA cell takes 40 – 56 days from creation to
sloughing off
►Stratum basaleStratum basale Deepest layer of epidermisDeepest layer of epidermis Cells actively undergoing cell divisionCells actively undergoing cell division New cells push older cells upward until they New cells push older cells upward until they
eventually fall offeventually fall off Cells are mostly Cells are mostly keratinocyteskeratinocytes and some and some
melanocytesmelanocytes
Layers of the EpidermisLayers of the Epidermis
KeratinizationKeratinization► KeratinKeratin is a protein that helps harden skin cells, is a protein that helps harden skin cells,
makes them tougher and helps prevent water makes them tougher and helps prevent water loss by the body.loss by the body.
► KeratinocytesKeratinocytes are areresponsible for responsible for making keratinmaking keratin
Keratin is found in cells of the basale and
spinosum strata
Keratin makes the skin waterproof
► Stratum spinosumStratum spinosum – – Made of Made of keratinocyteskeratinocytes Some cells grow Some cells grow
projections that projections that connect to other connect to other cells making the cell cells making the cell layer strongerlayer stronger Prickle Cells with long
projections
Stratum granulosumStratum granulosum – – mostly flattened mostly flattened keratinocytes that have lost keratinocytes that have lost nuclei and organellesnuclei and organelles
Death zone of Death zone of keratinocyteskeratinocytes
Vitamin D ProductionVitamin D Production►Cells of stratum spinosum and basale:Cells of stratum spinosum and basale:
UV energy + cholesterol = Vitamin DUV energy + cholesterol = Vitamin D►Vitamin DVitamin D::
used by kidney to make the hormone used by kidney to make the hormone calcitriolcalcitriol
►CalcitriolCalcitriol:: necessary to signal small intestine to absorb necessary to signal small intestine to absorb
calcium from the bloodcalcium from the blood►No Vitamin D No Vitamin D no calcitriol no calcitriol no calcium absorption no calcium absorption weak bones weak bones
► Stratum lucidumStratum lucidum Formed from dead cells of Formed from dead cells of
the deeper layersthe deeper layers Occurs only in thick, Occurs only in thick,
hairless skin of the palms hairless skin of the palms of hands and soles of feetof hands and soles of feet
► Stratum corneumStratum corneum Outermost layer of Outermost layer of
epidermisepidermis Scale-like dead cells are Scale-like dead cells are
filled with filled with keratinkeratin which is which is a strengthening protein a strengthening protein also preventing water loss also preventing water loss from skinfrom skin
Layers of SkinLayers of Skin
No Lucidum Layer
MelaninMelanin
► Pigment (melanin) Pigment (melanin) produced by melanocytesproduced by melanocytes
► Melanocytes are mostly in Melanocytes are mostly in the stratum basalethe stratum basale
► Color is yellow to red to Color is yellow to red to brown to blackbrown to black
MelanocytesMelanocytes: Cells deep in the epidermis : Cells deep in the epidermis and dermis that produce a pigment called and dermis that produce a pigment called melanin which protects the cells from UV melanin which protects the cells from UV damagedamage
Skin color determined by the size and quantity of melanin
granules in the tissue
► Determined by genetic, environmental, and physiological Determined by genetic, environmental, and physiological factorsfactors Your DNA determines how much MELANIN is producedYour DNA determines how much MELANIN is produced UV radiation increases melanin productionUV radiation increases melanin production Circulation, vitamin deficiencies, physical ailments Circulation, vitamin deficiencies, physical ailments
(liver failure)(liver failure)
What’s your color?What’s your color?
Why the Why the Spots…?Spots…?
► Large amounts of Large amounts of melanin occur in some melanin occur in some regions like freckles, regions like freckles, moles, and nipples.moles, and nipples.
► Caused by uneven Caused by uneven distribution of melanindistribution of melanin
► Less melanin occurs in Less melanin occurs in the lips, hands, and the lips, hands, and soles of the feet.soles of the feet.
AlbinismAlbinism► A single gene mutation can cause a A single gene mutation can cause a
deficiency or complete absence of melanin.deficiency or complete absence of melanin.► Albinos have fair skin, white hairs, and Albinos have fair skin, white hairs, and
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 layerDermis – the middle layer► Papillary layer:Papillary layer:
extensions of the extensions of the dermis into the dermis into the epidermis epidermis
► Blood vessels Blood vessels nourish all hair nourish all hair follicles and bring follicles and bring nutrients and oxygen nutrients and oxygen to the lower layers of to the lower layers of epidermal cells epidermal cells
What makes us stay young What makes us stay young looking?looking?
►Elastic fibersElastic fibers gives skin elasticitygives skin elasticity fibers can stretch up to 1.5x fibers can stretch up to 1.5x
their length and snap back their length and snap back to their original length to their original length when relaxed when relaxed
►Collagen fibersCollagen fibers gives skin support/firmnessgives skin support/firmness ~ one quarter of the human body is collagen~ one quarter of the human body is collagen support the skin’s mechanical strength and support the skin’s mechanical strength and
texturetexture
Sensory Perception in SkinSensory Perception in Skin► Skin is highly sensitivity to touch Skin is highly sensitivity to touch
because of large amounts of because of large amounts of sensory structures found in dermissensory structures found in dermis
Sensory Sensory Perception in Perception in
DermisDermisMerkel cells:Merkel cells: deep layers of epidermis deep layers of epidermis
- superficial touch superficial touch
Free Nerve Endings:Free Nerve Endings: superficial dermis superficial dermis- pain and temperaturepain and temperature