Both endoderm and mesoderm contribute to the development of the liver, gallbladder and biliary system. In the 4th week of gestation, at the junction of the of the foregut and midgut, the primitive endoderm gives rise to a foregut diverticulum called the hepatic diverticulum . The mesodermal tissue for the liver appears on day 22 and is called septum transversum. This mesodermal tissue contributes to the development of the heart, diaphgragm and liver.
|
82219a01b2.8s 82219a02a1.8s |
The hepatic diverticulum has two components; a pars hepatcia and pars cystica. The pars hepatica will evolve into the liver and bile ducts while the pars cystica will develop into the gallbladder and cystic duct. The hepatic bud is initially a solid cord but by week 8 with growth and resorbtion the tubular components are canalized.
|
82219a02b1.8s 82219a02b3.8s |
Complex interactions between the mesoderm and the epithelial cells of the endoderm take place, but a harmonious marriage between the two systems has to take place in order for the appropriate connections between duct, parenchyma, connective tissue and vessels to evolve.
liver bile ducts pars cystica gallbladder and cystic duct. endodermal bud solid cord growth and resorbtion gallbladder embryology normal Davidoff art copyright 2008 82219b08.8s |
Additionally a series of growth patterns change the position of the organs. As the stomach grows it rotates to the left. The duodenum grows down and to the right and also rotates to the right. The combination of these three events brings the distal common bile duct, and ventral pancreas to the medial and left side of the duodenum. The distal common bile duct as a result of the rotations courses behind the duodenum, and the biliary pancreatic confluens connects to the middle of the descending duodenum on its medial aspect.
82219b12.8s liver gallbladder pancreas foregut midgut bile duct cystic duct common bile duct stomach embryology septum transversum mesoderm endoderm 5th week stomach rotated to left duodenum growth |
At the sixth week the extrahepatic biliary system becomes reorganized and recanalizes. At the 7th week the cystic duct recanalizes while the gallbladder recanalizes at a slightly later date.
In a histological study (Haffajee) embryos of 10-13weeks age, demonstrated thickened walls, and contained “crumbly” debris. At 14 weeks bile staining was observed, and the mucosa appeared mature. At 20 weeks bile with mature consistency and color was present.
Thus the gallbladder arises from the foregut, with precursors that are common to the liver and pancreas. it shares primitive tissue with the heart, diaphragm and gastrointestinal tract. It is initially a solid bud, undergoes cavitation, returns to solid form, only to recanalize again, maturing by 10-13 weeks. By 20 weeks mature bile, indicating a mature liver is found in the formed gallbladder.
Applied Biology
Sometimes the pars cystica, the precursor for the gallbladder, divides in two rather than remaining one entity, forming a duplicated gallbladder usually with one cystic duct. This results in a duplicated gallbladder.
04750 gallbladder duplicated gallbladders oral cholecystogram congenital duplication anomaly growth Davidoff MD |
82231c01.8s gallbladder duplicated congenital duplication CTscan Courtesy Ashley Davidoff MD copyright 2008 |
A range of underdevelopment can occur varying from hypoplasia to aplasia. Biliary atresia is a known association with infantile polycystic disease. In biliary atresia the intrahepatic ducts, extrahepatic ducts, and gallbladder are variably involved.
28814c02.8s gallbladder small absent hypoplastic intrahepatic bile ducts liver biliary atresia congenital cholangiogram Courtesy Ashley Davidoff MD copyright 2008 |
The positioning of the gallbladder is related to the positioning of the liver. In situs inversus of the abdominal organs, the gallbladder is left sided. If there is situs ambiguus, there are usually two large lobes of the liver, reminiscent of two right lobes, with one one on the right and one on the leftside. The ambiguity of the liver also affects the gallbladder and the confounded gallbladder is centrally placed. This entity occurs in the asplenia syndrome.
82222.8s liver gallbladder bilateral right lobe asplenia syndrome Ivemark syndrome central gallbladder situs ambiguus congenital position gross pathology Courtesy Ashley DAvidoff MD copyright 2008 |
References
Brookes Clinical Embryology: A Color Atlas and Text By Murray Brookes, Anthony Zietman Published by CRC Press, 1998
Meilstrup JW Imaging Atlas of the Normal Gallbladder and Its Variants By Jon W. Meilstrup Published by CRC Press, 1994
Suchy Liver Disease in Children By Frederick J. Suchy, Ronald J. Sokol, William F. Balistreri Published by Lippincott Williams & Wilkins, 2000 **