A. Thick skin
Slide 106 thick skin, sole of foot H&E View Virtual Slide
Slide 112 thick skin, sole of foot H&E View Virtual Slide
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Slide 112N thick skin, sole of foot H&E View Virtual Slide
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In this slide the structure of skin, especially the epidermis, is exaggerated in response to the continued stress and abrasion applied to the plantar surface of the foot. Study the epidermis in slides 106, 112, and 112N. Identify the various strata:
- Stratum basale (also known as S. germinativum): A single layer of cuboidal to columnar cells resting on and separated from the underlying dermis by a basal lamina. Mitotic figures occur in this layer.
- Stratum spinosum: Several layers in thickness. In reduced light, the cells appear interconnected by “spinous” processes.
- Stratum granulosum: A few layers of cells that are characterized by numerous, dense, basophilic granules. These are keratohyaline and membrane coating granules.
- Stratum corneum: Note the striking change in cellular morphology. The cells are flattened, devoid of nuclei or cytoplasmic granules, and filled with mature keratin (slide 112N). In slides 106 or 112, however, nuclei are still present in many cells of this layer, which are not normal. Because of differential dye penetration, the staining of the stratum corneum is variable and unpredictable. Sectioning artifacts are common.
The principal cell type of the epidermis is termed a keratinocyte and you will see this term used as a general descriptor for the epithelial cell found in any stratified squamous epithelium. Note the absence of blood vessels in the epidermis. Nourishment is obtained by diffusion from capillaries in the underlying dermis. The interface of the epidermis and dermis is uneven. A pattern of ridges and grooves on the deep surface of the epidermis fit a complementary pattern of corrugations of the underlying dermis. The projections of the dermis are called dermal papillae and those of the epidermis, epidermal ridges (pegs), because of their appearance in vertical sections of the skin. However, these terms are not always accurately descriptive of the three dimensional configuration of the region of interdigitation. With low power, identify the epidermal ridges and dermal papillae. What is the function of the epidermal ridges and dermal papillae
Note the finer arrangement of collagen fibers in the papillary dermis slide 112N papillary dermis View Image as opposed to that of the reticular dermis slide 112N reticular dermis View Image (refer back to slide 033 morphology and distribution of elastic fibers View Image in order to review the morphology and distribution of elastic fibers in the dermis). The fatty layer beneath the dermis, the subcutaneous connective tissue, is often called thehypodermis or superficial fascia. It is this layer that allows the skin to “move”.
B. Thin Skin
Slide 105-1 hair follicle H&E View Virtual Slide
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Slide 105-2 thin skin H&E View Virtual Slide
Slide 104-1 thin skin H&E View Virtual Slide
Slide 104-2 thin skin H&E View Virtual Slide
The epidermis in thin skin is much thinner and simpler in structure. Each stratum is thinner and the stratum granulosum may be absent. Melanocytes #105-1 melanocytes View Image (derived from neural crest cells) capable of producing the pigment melanin are numerous in the deeper (toward the base) layers of the epidermis. They can be identified by the presence of a nucleus surrounded by a clear space. The cells with brownish pigments are actually keratinocytes that have received melanin granules from the melanocytes by pigment donation. The slides 104-1 and 104-2 are skin samples from lighter and darker skinned individuals. It is not difficult to tell which sample is from which individual. Note the presence of portions of hair follicles and sebaceous glands in the dermis.
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