Epidermis:
-Made up of stratified squamous
-Lacks blood vessels
-has 4 layers in most areas, 5 layers in thick skin
-Stratum Basale (stratum germinativum) is the deepest layer; consists of dividing cells; well nourished by dermal blood vessels
-Basal cells divide, older cells, called Keratinocytes (due to accumulation of fibrous protein, keratin) migrate toward skin surface
-As keratinocytes migrate outward, they harden, dehydrate, & die which is a process called keratinization
-Epidermis is important because it protects against water loss, mechanical injury, chemicals, & microorganisms
4 Layers of Epidermis: + 5th layer in thick skin:
-Stratum Basale: innermost layer, dividing layer
-Stratum Spinosum
-Stratum Granulosum
-Stratum Corneum: outermost layer; dead, flattened, keratinized cells; constantly being shed from outer skin surface
-Stratum Lucidum: layer between stratum granulosum & stratum corneum, found only in thick skin of palm & soles of feet
Epidermis; Melanocytes:
-Special cells that produce pigment, melanin
-found in deepest layer of epidermis & in dermis
-Melanin protects DNA of skin cells against damaging effects of UV Radiation form sun
-Melanin pigment gives sun & hair color; more melanin is present the darker the skin and hair will be