Epithelial cells are essential to the survival and homeostasis of complex organisms. These cells cover the surfaces of all mucosae, the skin, and other compartmentalized structures essential to physiological function. In addition to maintenance of barriers that separate internal and external compartments, epithelia display a variety of organ-specific differentiated functions. Function is reflected in overall epithelial structure and organization, shape of individual cells, and proteins expressed by these cells. More than one epithelial cell type is often present within a single organ and, in many cases, individual cells differentiate to change their functional behaviors as part of normal development or in response to extracellular stimuli. This article discusses the diversity of epithelial structure and function in general terms and explores representative tissues in greater depth to highlight organ specific functions and their contributions to physiology and disease. © 2017 American Physiological Society. Compr Physiol 7:1497-1518, 2017.
Copyright © 2017 John Wiley & Sons, Inc.