Epithelial cells

Epithelial cells line the surface of the intestine, lung, kidney, and liver and form regulated boundaries between compartments within an organism. By forming a barrier between disparate environments, epithelial cells play a number of important roles in regulating host physiology. They prevent dissipation of concentration gradients between the compartments they separate. They also keep endogenous bacteria, microbial products, and bioactive substances from escaping their internal environment in the gut lumen and lung by acting as a fence preventing translocation of these products into the systemic circulation or lymph. Epithelial cells also have a crucial role in microbial surveillance, communicating with immune cells through cytokines and chemokines. Finally, gut epithelial cells regulate the absorption and secretion of fluids, electrolytes, and nutrients. With the exception of increased apoptosis in the gut, histologic analysis of the epithelium is unremarkable in either human autopsy studies of critical illness (1) or murine models of sepsis (2). Nonetheless, multiple studies suggest that epithelial dysfunction plays a crucial role in the pathogenesis of organ failure (3). This review will focus on how critical illness worsens epithelial barrier function through alterations in the structure and function of tight junctions and how changes in epithelial apoptosis may contribute to organ dysfunction. Epithelial Barrier Dysfunction in Critical Illness

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