Structure of the dermal matrix during development and in the adult

To describe a normal adult dermis is a seemingly simple task considering the diverse microscopic methods available for examination of the tissue, staining procedures to delineate the fibrous and cellular components, and immunolabeling techniques to identify precisely the various fibrous elements. Yet it is not simple because the range of normal in any of the dermal components has never been surveyed. There are well recognized age-related changes in the dermis; the tissue can be modified by environmental insults (e.g., actinic damage) and alterations can occur in tissue of individuals with inherited disorders of connective tissue metabolism, other metabolic diseases (e.g., diabetes) and in those receiving topically applied or systemic medication. From our own experience there is also marked individual variability (at any age) in the connective tissue architecture and its fibrous components. Thus, we are describing the structure of a normal dermis without demonstrating the range of normal in any one of its elements. Reference will occasionally be made to abnormal conditions of the matrix since through these deviations it is possible to understand more about the normal. Structural and biochemical properties of the dermal connective tissue in human embryos and fetuses have been described in a number of studies, but in only a few instances was the goal of the research focused on this problem; instead, fetal tissue was used for comparative purposes in aging studies, or a certain characteristic of the fetal dermis was pointed out along with the description of another structure (e.g., hair follicle). In the few instances where a sequential study was carried out on one matrix component during development, an animal (pig, chick) was selected for the work.