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Answer:
Epidermis.
It is composed of keratinized, stratified squamous epithelium and is made up of 4 layers of epithelial cells depending on its location in the body. From deeper to superficial these layers are stratum Basale, stratum spinosum, stratum granulosum, and stratum corneum. The cells in all the layers except for stratum besele are called keratinocytes which is a cell that manufactures and stores the protein keratin.
Stratum Basale.
It is a cuboid-shaped stem cell that is a precursor of the keratinocytes of the epidermis. Two other cell types found in this basal cell are Merkel cells which function as a receptor and are responsible for stimulating sensory nerves that the brain perceives as touch. The second is melanocyte that produces melanin pigment which gives the skin its color.
Stratum spinosum.
It is spiny in appearance due to the protruding cell processes that join the cells via a structure called desmosome. The desmosome cell interlock with each other to strengthen the bond between the cell. Keratinocytes in the stratum spinosum stats synthesizing keratin and release water-repelling glycolipid that helps to prevent water losses from the body.
Stratum granulosum.
They are grainy in appearance due to further change in keratinocytes as they are pushes from the stratum spinosum. The cells become flat as their membrane thickens to allow the production of protein keratin which accolades as lamellar granules within the cells.
Stratum Lucidum.
It is a smooth and translucent layer of the epidermis situated above the stratum granulosum. Keratinocytes containing these cells are dead and flat. Stratum lucidum cells are packs with eleiden derived from keratohyalin which give these cells their transparency and provide a barrier to water.
Stratum corneum.
This is the most superficial layer in the epidermis and it prevents penetration of microbes and dehydration of underlying tissues.
Dermis.-This is the inner layer of the skin and has the following functions.
Reticular layer
Just below the papillary layer, we have a much thicker layer called the reticular layer composing of dense connective tissue. It contains elastin fibers providing elasticity to the skin enabling movement.
Hypodermis
Explanation:
Keratinocytes
- Keratinocytes produce a wide variety of cytokines that have important roles in mediating cutaneous immune responses, inflammation, wound healing, and the growth and development of certain neoplasms.
- Keratinocytes also produce eicosanoids, prostaglandin (PG) E2, and neuropeptides such as propiomelanocortin and α MSH.
- In the basal layer of the skin, the innermost stratum, a basal keratinocyte has just divided by mitosis to form a new basal keratinocyte.
- This new cell starts to divide itself and produces many more keratinocytes.
- The keratinocytes from the squamous layer are then pushed up through two thin epidermal layers called the stratum granulosum and the stratum lucidum.
- As these cells move further towards the surface of the skin, they get bigger and flatter and adhere together, and then eventually become dehydrated and die.
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