Stratified Squamous epithelium, Keratinized

Stratified epithelium is classified by the cell type on the uppermost layer.  Notice that is true for the pictures shown below.  They are typically found in locations where constant abrasion is likely, such as skin.  The epithelium at these locations have varying thickness of Kertain on top, and thus are classified as Keratinized.  In other words, the uppermost layer of cells are dead.

Because the uppermost layer of cells are regularly sloughed off by abrasions, they are constantly replenished by an actively dividing basal layer.  The basal layers tend to be more cuboidal in shape and the cells being pushed outward gradually take on the flattened morphology.  In keratinized epithelium, the cells also produce keratin as they move upward, forming a layer of keratin as the cells die.  This layer of keratin forms the barrier to protect against excessive water loss and foreign substances invasion.

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Thick skin.  Notice the layer of basal cell that demarcate between the epithelial tissue above and the connective tissue below.  (TM: 100x, picture taken with an Olympus DPlan 10/0.25 on Sony NEX-6)
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Epidermis of Thick skin.  Notice the clear white band that demarcate between the living cells (under) and dead cells/keratin layer (above).  This clear layer is a distinctive characteristic of thick, plantar skin.  Annotated version here.  (TM: 100x, picture taken with a Nikon Planapo 10/0.4 on Sony A7ii)
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Epidermis of Thick skin.  Notice the layers of skin shown from right to left: Stratum corneum, stratum lucidum (the clear white layer), stratum granulosum, stratum spinosum, statum basale.  Annotated version here.  (TM: 400x, picture taken with a Zeiss Planapo 40/1.0 Oil on Sony A7ii)
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Thin skin.  Notice the relatively thin layer of keratin on top.  (TM: 100x, picture taken with an Olympus DPlan 10/0.25 on Sony NEX-6)
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View of another specimen of thin skin (Scalp).  (TM: 100x, picture taken with a Nikon Planapo 10/0.4 Oil on Sony A7ii)
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Epidermis of thin skin.  Notice the absence of the clear layer (stratum lucidum).  (TM: 400x, picture taken with a Zeiss Planapo 40/1.0 Oil on Sony A7ii)

 

 

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