Lung Injury and Repair in COVID-19 related Acute Lung Injury

The alveolar epithelium is the largest surface area of the body in continuous contact with the outside environment and is critical for effective gas exchange to support metabolism. The alveolar walls consist of three distinct layers: the alveolar epithelium, comprising type I and type II alveolar epithelial cells; a matrix scaffold; and the microvascular endothelium. Most of the alveolar surface is covered by thin type I epithelial cells that cover the matrix framework and are closely opposed to microvascular endothelial cells.