Development of the body cavities and the diaphragm

1. Development of the body cavities and the diaphragm

2. Development of the liver • The liver bud or hepatic diverticulum is formed from an outgrowth of the endodermal epithelial lining of the foregut . • The epithelial liver cords and primordia of the biliary system which develop from the hepatic diverticulum, grow into the mesenchymal septum transversum . • Between the layers of the ventral mesentery, derived from the septum transversum, these primordial cells differentiate into the parenchyma of the liver and the lining of the ducts of the biliary system.

3. Hemopoiesis in the liver starts on week 6. • Bile formation starts on week 12.

4. Development of the pancreas • The pancreas is formed by dorsal and ventral pancreatic budsoriginating from the endodermal lining of the foregut. • When the duodenum rotates to the right, the ventral pancreatic bud moves dorsally and fuses with the dorsal pancreatic bud. • The ventral pancreatic bud forms most of the head of the pancreas and the dorsal pancreatic bud forms the rest. • If the duct systems from each pancreas fail to fuse, an accessory pancreatic duct forms.

5. The intraembryonic coelom is the primordium of the embryonic body cavities and begins to develop near the end of week 3. • By the beginning of week 4, it is a horseshoe-shaped cavity in the cardiogenic and lateral mesoderm.

6. The curve of the horseshoe represents the future pericardial cavity and its lateral limbs represent the future pleural and peritoneal cavities.

7. During folding of the embryonic disc in week 4, the lateral parts of the intraembryonic coelom are brought together on the ventral aspect of the embryo.

8. When the caudal part of the ventral mesentery disappears, the right and left parts of the intraembryonic coelom merge and form the peritoneal cavity.

9. As the peritoneal portions of the intraembryonic coelom come together, the splanchnic layer of themesoderm encloses the primitive gut and suspends it from the dorsal body wall by a double-layered peritoneal membrane known as the dorsal mesentery.

10. Until week 7, the embryonic pericardial cavity communicates with the peritoneal cavity through paired pericadioperitoneal canals

11. During weeks 5 and 6, partitions form near the cranial and caudal ends of these canals: • Fusion of the cranialpericardiopleural membranes withmesoderm ventral to the esophagus separates the pericardial cavity from the pleural cavities. • Fusion of the caudal pleuroperitoneal membranes, during formation of the diaphragm, separates the pleural cavities from the peritoneal cavity.

12. The diaphragm forms from : • 1) the septum transversum, • 2) the pleuroperitoneal membranes, • 3)ventral the dorsal mesentery of the esophagus, • 4) the body wall.(mesorerm)

13. Anomalies • Diaphragmatic Hernias. • A. Posterolateral. • B. Posterior. • C. Retrosternal. • D. Central.

14. A posterolateral defect of the diaphragm results in congenital diaphragmatic hernia and is due to failure of fusion between the pleuroperitoneal membranes and other diaphragmatic components.