Exam 2 Review:  Chapter 5:  Epidermal Histology

keratinization - The process of converting (something, e.g., epidermis, hair, nails, horns, and hooves) into keratin.

keratohyaline - The protein precursor to keratin which is the predominant form of the protein observed in keratinocytes in the stratum granulosum of the epidermis of the skin.

keratin - A tough, insoluble protein, produced by keratinocytes, which is the predominant form of the protein in the stratum lucidum and stratum corneum of the skin; it helps protect the epidermis from abrasion and water loss; keratin is also the chief structural constituent of hair, nails, horns, and hooves.

keratinocytes - The vast majority of cells comprising the stratified squamous epithelium of the epidermis which produce keratin and then die, forming the protective outer layers of the skin which are continually being sloughed; these tightly packed cells are held together by desmosomes.

melanocytes - A small set of spider-shaped epidermal cells restricted to the stratum germinativum (10 - 25% of the basal cells) which synthesize the brown/black pigment melanin and then package the melanin in melanosomes which are transferred to keratinocytes; their melanin output is determined by an individual's heredity and by the environmental stimulus of exposure to uv radiation from sunlight.

epidermal dendritic cell = Langerhans' cell - A star-shaped wandering macrophage derived from the bone marrow which infiltrate the epidermal layers and serve the immune functions of phagocytosis and antigen-presentation.

Merkel cell - An exteroreceptor located in the stratum germinativum of the epidermis; a small receptor resembling a spiky hemisphere which communicates with the disk-like sensory terminal of a neuron; the combined structure is termed a Merkel or tactile disc; they are receptors for light or discriminative touch.

stratum basale = stratum germinativum - The basal layer of the stratified squamous epithelium of the epidermis which consists primarily of the youngest cuboidal keratinocytes which are undergoing mitosis to produce the rest of the keratinocyte layers of the epidermis, as well as a few melanocytes, Merkel cells, and epidermal dendritic = Langerhans' cells.

stratum spinosum - The second deepest layer (from the basal layer) of the stratified squamous epithelium of the epidermis, several cell layers thick, which consists primarily of developing irregularly-shaped keratinocytes ("prickle cells") which are synthesizing prekeratin filaments.

stratum granulosum - The third deepest layer (from the basal layer) of the stratified squamous epithelium of the epidermis, three to five cell layers thick, which consists primarily of flattening spindle-shaped keratinocytes which are synthesizing keratinohyaline and water-proofing glycolipids.

stratum lucidum - The fourth deepest layer (from the basal layer) of the stratified squamous epithelium of the epidermis, a few cell layers thick (the "clear layer") located between the stratum granulosum and the stratum corneum, which only appear in the thick skin of the palms of the hands and soles of the feet, which consists primarily of flattening dead keratinocytes which have a relatively clear cytoplasm.

stratum corneum - The outer protective layer ("horny layer") of the stratified squamous epithelium of the epidermis, 20 to 30 cell layers thick, which consists primarily of flattened dead keratin-filled keratinocytes which are regularly sloughed in response to friction.

List:

 3. four cell types found in the epidermis and describe the function of each.

          keratinocyte - form the protective outer layers of the skin
          melanocyte - synthesize the brown/black pigment melanin which is transferred to keratinocytes to provide protection against uv light radiation
          epidermal dendritic cell = Langerhans' cell - wandering macrophage which perform the immune functions of phagocytosis and antigen-presentation
          Merkel cell - sensory receptor for light or discriminative touch

 4. five layers of the epidermis from superficial to deep.

                    [apical (free) surface]
          stratum corneum
          stratum lucidum [only in the thick skin of the palms of the hands and soles of the feet]
          stratum granulosum
          stratum spinosum
          stratum basale = stratum germinativum
                    [basal surface]

Sketch and label, etc.

1. an illustration of the layers of the epidermis of the skin.