Epidermis
Characteristics of the epidermis:
• Made up of stratified squamous epithelium
• Lacks blood vessels
• Consists of 4 layers in most areas, 5 layers in thick skin
• Stratum basale (or stratum germinativum) is the deepest
layer; it consists of dividing cells; it is well-nourished by dermal blood vessels
• As 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, and die, in a process called keratinization These 4 layers of the epidermis are found in all areas of the body:
• Stratum basale: innermost layer, dividing layer
• Stratum spinosum
• Stratum granulosum
• Stratum corneum: outermost layer; dead, flattened, keratinized cells; these are continually being shed from the outer skin surface
• Stratum lucidum: layer between the stratum granulosum and the stratum corneum, which is found only in the thick skin of the palms and soles
• The epidermis is important because it protects against water loss, mechanical injury, chemicals, and microorganisms