the expanded lung. this leads to a smaller volume of gas exchanged per breath. pulmonary alveolar microlithiasis is a rare lung disorder of small stone formation in the alveoli. fluid a pulmonary contusion is a bruise of the lung tissue caused by trauma. damaged capillaries can cause blood and other fluids to accumulate in the tissue of the lung, impairing gas exchange . pulmonary edema is the buildup of fluid in the parenchyma and alveoli usually caused by left ventricular heart failure, or by damage to the lung or its vasculature. coronavirus further information: ace2 § coronavirus entry point because of the high expression of angiotensin-converting enzyme 2 (ace2) in type ii alveolar cells, the lungs are susceptible to infections by some coronaviruses including the viruses that cause severe acute respiratory syndrome (sars) and coronavirus disease 2019 (covid-19). additional images blood circulation around alveoli diagrammatic view of lung showing magnified inner structures including alveolar sacs at 10) and lobules at 9).