Cell and Tissue Organization

The aim of this chapter is to provide an introduction that will serve the following chapters. An understanding of normal cell and tissue organization is essential to being able to conceptualize changes that occur preceding the development of malignancy. Initial tissue progression takes place after fertilization and gastrulation, and then cell phenotypes specialize as specific tissues develop. Through morphogenesis and organogenesis, tissues described here are those of the gastrointestinal tract with the pancreas, liver, and lung; the primordial germ cells and gonads; vasculature and blood progenitor cells; central nervous system; epidermis; and breast. These have been chosen as they are amongst the most common sites in which primary malignancies are found. Normal, adult parenchymal cells of these are briefly explained, followed by a concise description of stem cell niches, where cancer stem cells might reside. Keywords: morphogenesis; differentiation; organogenesis; normal parenchyma; embryonal rest hypothesis; cancer stem cells