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Integration of Embryology and Histology

Developmental anatomy can be used to organize the teaching of histology. Since certain tissues are derived from predictable embryonic layers or structures, the embryological organization can be used to organize tissues in a meaningful and useful manner. We offer several examples of this relationship to help students organize tissues by their developmental origins. First, all functional neurons originate from ectoderm, but the fate of cells coming from the neural tube differs from those that come from the neural crests. All neurons that have their final location within the central nervous system (CNS) are derived from the neural tube, whereas neurons whose nerve cell bodies are outside the CNS come from the neural crests. Second, almost all muscle tissue, which comprises about 40% of the human body mass, comes from the mesoderm. The exceptions are the smooth muscle cells within the eye, which are derived from the neural crest. Almost all connective tissues, with the exception of the notochord, are derived from the mesoderm, or more specifically from mesenchymal cells. Melanocytes (also satellite cells and Schwann cells) are derived from neural crest. Epithelial cells that contribute to the epidermis are derived from ectoderm, and almost all other epithelial tissues are derived from endoderm. Exceptions are endothelial cells (including endocardium) that come from mesoderm. This outlines the close relationship between developmental anatomy and histology that helps to categorize tissues by their embryologic origin.