The papillary dermis is approximately 300-400 µm deep.This depth is variable and depends upon such factors as ageand anatomical location. Typically, the superficial portionof the papillary dermis is arranged into ridge-like structures,the dermal papillae, which contain microvascular and neuralcomponents that sustain the epidermis (Cormack, 1987). Dermalpapillae greatly extend the surface area for epithelial-mesenchymalinteractions and delivery of soluble molecules to the epidermis.A vascular plexus, the rete subpapillare, demarcates the lowerlimit of the papillary dermis (Figs 1, 2). The reticular layerof the dermis extends from this superficial vascular plexusto a deeper vascular plexus, the rete cutaneum, which servesas the boundary between the dermis and hypodermis. Hair folliclesand their associated dermal cells extend into and often throughthe reticular dermis to terminate in the hypodermis, a tissuerich in adipocytes.
Mechanical separation of skin (dermatoming) into defined papillaryand reticular layers allows establishment of explant culturesof cells from each layer. Papillary fibroblasts divide at fasterrates than do site-matched reticular fibroblasts (Harper andGrove, 1979; Azzerone and Macieira-Coelho, 1982; Schafer etal., 1985; Sorrell et al., 1996; Sorrell et al., 2004). Reticulardermal fibroblasts seeded into type I collagen lattices contractthem faster than do papillary dermal fibroblasts (Schafer etal., 1985; Sorrell et al., 1996). When grown to confluence inmonolayer culture, the papillary cells attain a higher celldensity partly because they are not fully contact inhibited(Schafer et al., 1985; Sorrell et al., 2004).