Epidermisthe outermost layer of the skin

Epidermis

• "epi" in Greek meaning "over" or "upon"• serves as a barrier to protect against microbial

pathogens, oxidant stress(UV light) and chemical compounds and provides mechanical resistance.

• it protects the body from a possible injuries.

Parts of Epidermis

• Stratum Corneum (Horned Layer)-to form a barrier to protect the underlying tissue

from infection, dehydration, chemicals.-this layer is responsible for the "spring back" or

stretchy properties of skin. A weak glutenous protein bond pulls the skin back to its natural shape.

- contains 20 layers of dead cells.-it is permanent and is replaced only during times of

rapid growth, in a process called ecdysis or moulting.

• Stratum Lucidum (Clear Layer)-is a thin, clear layer of dead skin cells in the

epidermis named for its translucent under the microscope.

-it is readily visible by light microscopy only in areas of thicker skin, which are found on the palms of hand and the soles of the feet.

-they are flattened. They are sorrounded by an oily substance that is the result of the exocytosis of lamellar bodies accumulated while the keratinocytes are moving through the stratum spinosum and stratum granulosum.

• Stratum Gronulosum (Granular Layer)– is a thin layer of cells in the epidermis.

Keratinocyte migrating from the undelying stratum spinosum become known as granular cells in this layer, This cells contain keratolyalin granules, which are filled with proteins that promote hydration and crosslinking of keratin.

Keratinocytes-is the formation of barrier against environment

damage such as pathogens, heat, UV radiation and water loss.

• Stratum Spinosum-this layer is also reffered to as the "spinous" or

"prickle-cell" layer.-this layer is composed of polyhedral keratinocytes,

they have large pale staining nuclei as they are active in synthesizing fibrils proteins, known as cytokeratin, which build up within the cells aggregating together forming tonofibrils.The tonofibrils go on to form the desmosomes allowing strong connections to form between adjacent keratinocytes.

• The stratum basale – is primarily made up of basal keratinocyte cells,

which can be considered the stem cells of the epidermis. They divide to form the keratinocytes of the stratum spinosum, which migrate superficially. Other types of cells found within the stratum basale are melanocytes (pigment-producing cells), Langerhans cells (immune cells), and Merkel cells (touch receptors).

– the stratum basale (basal layer, sometimes referred to as stratum germinativum) is the deepest layer of the five layers of theepidermis, which is the outer covering of skin in mammals.