Outermoust superficial region of the skin

• Composed of keritinized stratified squamous epithilium consisiting of four distinct cell types (melanocytes, markel cells, and Langerhans's cells) and four or five layer.
• Functions in protection.

• Most abundent cell type in epidermis
• Function: protection from
• Keratinocytes are connected tightly to one another via desmosomes
• Arise from the stratum basale and are then pushed upwards to the epidermis. When they reach the surfface they are dead and the plasma membrane is filled with keratin.

Cells that synthesize melanin

• Spider-shaped
• Found in the deepest layer of the epidermis.
• Melanin accumulates in vesicles called melanosomes.
• Melanocytes are moved along actin filaments by motor proteins to the ends of the melanocyte's processes and are then taken up by keratinocytes.
• Gives the keratinocytes a pigment shield, they cluster over the nucleu of the keratinocytes on the side towards the skins' surface
• Many types of mutations can cause problems with function of melanocytes: melanoblast development migration, melanin synthesis, melanosome formation, transfer to keratinocytes.

• Melanin: yellow to reddish-brown to black pigment, responsible for darker sin colors
• Carotene: yellow to orange pigment, most obvious in the pams and soles of the feet (remember, carrot-->orange)
• Hemoglobin - reddish pigment responsible for the pinkish hue of the skin  (remember, hemoglobin --> blood-->red)

• Jaundice: Results in a yellowish tint to the skin. Caused by the liver's inability to excrete bile, thus causing bilirubin, a yellow pigment, to accumulate in body fluids. 
• Iron Overload - The buildup of iron in one's body. Results in skin turning a bronzed color.
• Vitilgo - The loss of melanocytes from dying off or the inability to function (possibly an immune response). Results in the loss of pigments in the skin.

Skin: Epidermis - Langerhan's cells

Immune cells (dendritic).

• Phagocytes
• Star-shaped cells
• Arise from bone marrow

Touh cells (tactile)

• Found at epidermal-dermal junction
• Associated with sensory nerve ending, sensory receptor for touch.
• The least numerous of epidermal cells

• The engulfing of large particles by forming projecting pseudopods ("false feet") around them and enclosing them within a membrane sac called a phagosome.
• Types of phagocytes: neutrophils, monocytes, macrophages, dendritic cells, mast cells

• Basal layer, deepest epidermal layer, firmly attached to the dermis.
• Typically a single layer of cells; contains the youngest keratinocytes.
• Cells there undergo rapid devision, hence its alternate name: stratum geminativum (think begging layer, thus new/most growth)
• 1-25% of cells in this layer are melanocytes
• This layer forms epidermal ridges, the patterns of which are responsible for fingerprints.

• Cells contain a weblike system of intermediate filaments attach by desmosomes.
• Several layeral layers thick.
• This layer cotains Keratinocytes irrregular in shape "prickle cells" (an artifact of processing); Melanin granules, and Langerhans' cells.

• Thin, only 3 to 5 cell layers.
• Cells have stopped dividing.
• There is an accumulation of keratohyaline (to form keratin) and lamellated granules (containing glycolipid, it is exocytosed into etracellular space to slow water loss)