1. The epidermis is mostly made up of keratinocytes, which form a stratified squamous keratinized epithelium. Three other types of epidermal cells are far less common: Merkel cells are pigment-producing melanocytes, antigen-presenting Langerhans cells, and tactile epithelial cells. The stratum corneum, Stratum lucidum, Stratum granulosum, Stratum spinosum, and Stratum basale are the five primary layers. The most superficial layer, the stratum corneum, is made up of 20-30 layers of dead, flattened, anucleate, keratin-filled keratinocytes. It protects against water loss and friction. Only thick skin has stratum lucidum, which is made up of 2-3 layers of anucleate, dead cells. The stratum granulosum is made up of 3-5 layers of keratinocytes, each having its kerato-hyaline granule. The stratum spinosum is made up of numerous layers of keratinocytes that are all linked together by desmosomes. Langerhans cells can also be found in this layer. The deepest layer is the stratum basale. In contact with the basement membrane, it is a single layer of cuboidal to low columnar cells. Melanocytes and Merkel cells can also be found here, as well as mitosis.
2. The dermis is a connective tissue layer that supports and links the epidermis to the subcutaneous tissue (hypodermis). The thickness of the dermis varies by body area and reaches a maximum of 4 millimeters on the back. The papillary and reticular layers of the dermis are two sublayers with ambiguous borders. The dermal papillae are located in the thin papillary layer, which is made up of loose connective tissue, fibroblasts, and scattered mast cells, dendritic cells, and leukocytes. The reticular layer underneath the papillary layer is substantially thicker, with more fibers and fewer cells than the papillary layer, and is made up of dense irregular connective tissue (mostly type I collagen bundles).
3. Hair follicles are made up of epithelial pockets that extend deep into the dermis and are connected to the superficial epidermis. A hair follicle creates a bulb around the dermal papillae, which are specialized dermal cells.