Ultrastructural organization of skin: classification on the basis of mechanical role.

In our previous developmental study on skin we reported that correlations existed between the collagen fibril diameter distribution, glycosaminoglycan content and composition, and mechanical role. In this work we present new but related electron microscope data on the ultrastructure of skins from flounder, marlin, cod, frog, toad, caiman, viper, pigeon, whale and opossum. It is shown that mammalian and avian body skins generally contain relatively sharp unimodal distributions of fibril diameter consistent with a "passive" mechanical role. In contrast most reptilian and fish skins have broad, right-skewed (or bimodal) distributions of fibril diameters compatible with the exotendinous attributes required of an "active" skin. A study of the changing form of the collagen fibril diameter distribution with depth in the dermis is also reported.