Lung and pleural cavities

Origin of the pleural cavities

At S10, the cranial part of the intra-embryonic coelom that is closed to the outside consists of a middle part, the pericardial cavity, and two thin lateral canals, the pericardioperitoneal canals. The pericardioperitoneal canals connect the pericardial cavity to the open part of the intra-embryonic coelom, which becomes the peritoneal cavity. At S13, the lung buds grow from a medial position towards the pericardioperitoneal canals and invaginate them. Due to the increasing size of the lung primordia, the pericardioperitoneal canals widen to become the pleural cavities. The inner layer of the pleural sac covers the lung primordium and becomes the visceral pleura; the outer layer attaches to the body wall, and becomes the parietal pleura. Each pleural cavity becomes separated from the pericardial cavity by the pleuropericardial membrane and from the peritoneal cavity by the pleuroperitoneal membrane.