Gartner_BRS Cell Biology & Histology, 9e

Chapter 12 Skin

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III. DERMIS

The dermis is the mesoderm-derived connective tissue layer of the skin that underlies the epidermis. Dermis consists of two ill-defined sublayers, the thin, superficial papillary layer and the deeper , more extensive reticular layer (see Table 12.1). A. The superficial papillary dermis is thin , uneven (see Fig. 12.2), and forms dermal ridges ( dermal papillae ), which interdigitate with the epidermal downgrowths ( epidermal ridges ), forming the epidermal-dermal junction. The papillary layer is composed of loose connective tissue containing fibroblasts, type III collagen fibers, fine elastic fibers, and capillary loops. Fine touch receptors, tactile corpuscles ( Meissner corpuscles ), are present in this layer and provide discriminatory sensations between two touch points on the skin. Fine, unmyelinated nerve fibers course through the papillary layer and extend into the extracellular spaces of the epidermis, where they function as pain receptors. B. The deeper reticular dermis is much thicker and constitutes the majority of the dermis. It is composed of dense irregular connective tissue rich with type I collagen fibers and thick elastic fibers . In its deeper aspects, it may contain lamellar corpuscles ( Pacinian corpuscles ) ( Fig. 12.4 ), which are pressure receptors, as well as bulboid corpuscles ( Krause end bulbs ), which were formerly thought to be cold receptors, but their actual function is uncertain. Specialized diffuse receptors are discussed in Chapter 19. C. Skin appendages are present in various locations and depths of the dermis, including the two types of sweat glands (eccrine and apocrine), sebaceous glands, hair follicles, and nails.

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FIGURE 12.4. Light micrograph of eccrine sweat glands and a lamellar (Pacinian) corpuscle in the dermis of the skin. Sweat glands are also present in the hypodermis among adipose cells (arrowhead). The secretory units (S) of the sweat glands are wrapped by fingerlike processes of myoepithelial cells and stain more lightly than the ducts (D) that are lined by a stratified cuboidal epithelium. This Pacinian corpuscle (P) lies deep in the dermis and is com posed of a centrally located nerve (n) surrounded by concentric layers of connective tissue. The nuclei of fibroblasts are seen, and so is a capillary (arrow), which helps to nourish the structure. Pacinian corpuscles are mechanorecep tors that respond to deep pressure ( × 150).