Structure of the 5 layers of the skin

Stratum corneum – outermost layer composed of 20-30 layers of dead, flattened cells; anucleate, keratin-filled keratinocytes which protect against friction and water loss

Stratum lucidum – 2-3 layers of anucleate, dead cells; seen only in thick skin on the palm of the hands and fingers, and soles of the feet

Stratum granulosum – 3-5 layers of keratinocytes with distinct keratohyalin granules; keratinocytes produce lipids and a natural moisturizing factor that makes the skin waterproof and holds moisture

Stratum spinosum – several layers of keratinocytes all joined by desmosomes to prevent the skin from tearing and blistering; Langerhans cells are present

Stratum basale – deepest, a single layer of cuboidal to low columnar cells in contact with basement membrane; mitosis occurs here; melanocytes and Merkel cells are present

Structure of the nail

Root – appears as a white crescent (lunula); embedded in the skin and adheres to an epithelial nail bed; produces most of the volume of the nail

Nail bed – an extension of the stratum basale beneath the nail; contains blood vessels, nerves, and melanocytes that produce melanin

Body – visible attached portion

Free edge – grows out away from the body

Nail fold – skin folds that overlap the borders of the nail

Eponychium – thick proximal nail fold commonly called the cuticle

Nail matrix – thickened proximal part of the nail bed containing germinal cells responsible for nail growth

Lunula – proximal region of the thickened nail matrix, which appears as a white crescent