University:
Stanford University
Course:
MED 101 | Human Anatomy
Academic year:

2023
Views:

92

Pages:

2
Author:

larbi43100

Development of digestive glands The digestive glands annexed to the digestive tract (liver and gallbladder, pancreas) derive from the endoderm of the primitive digestive tract by budding in the mesos. The secretory cells and excretory ducts of these organs differentiate from the endoderm while the surrounding mesenchyme will give rise to the remainder of the walls and supporting tissue. 1. Liver development From the beginning of the 4th week, a budding appears on the ventral side of the distal end of the foregut which gives rise to the hepatic diverticulum. The endoderm proliferates in the ventral midgut towards the septum transversum. It grows quickly and quickly occupies a large part of the abdominal cavity. The endodermal cells of the distal part of the bud differentiate into hepatocytes which will constitute, with the vascular primordia, the hepatic parenchyma and are at the origin of the intrahepatic bile ducts. The proximal part of the liver bud extends into the extrahepatic bile ducts and the bile duct which connect the gland to the duodenum. The liver is covered with peritoneum over its entire surface except in its upper part in contact with the diaphragm. From the 4th week, the liver ensures a hematopoietic function, with blood stem cells developing in the surrounding mesenchyme. 2. Gallbladder At the end of the 4th week, budding appears on the underside of the common bile duct. This bud elongates and dilates to form the gallbladder, its proximal part thins to form the cystic duct which connects the gallbladder to the common bile duct. Bile synthesis begins in the liver at the 12th week, when the gallbladder, cystic ducts and common bile duct are permeable, bile pigments are responsible for the coloring of the meconium. 3. Pancreas The pancreas derives from the development of two initial buds, originating from a proliferation of endoderm from the distal end of the foregut. The dorsal bud appears on the 26th day in the dorsal mesoduodenum; a few days later, the ventral bud appears in the ventral mesoduodenum, in the angle formed by the common bile duct with the duodenum. The endodermis gives rise to exocrine cells and excretory ducts, as well as to the various endocrine cells of the islets of Langerhans. Initially dispersed in the parenchyma, these cells subsequently come together in clusters to form the endocrine islands of the pancreas. At the 5th week, the ventral bud rotates to the right around the duodenum to fuse posteriorly with the dorsal bud. terminal ends in the duodenum at the level of the main papilla on its left wall (hepatopancreatic ampulla). Usually, fusion of the pancreatic buds is accompanied by fusion of the excretory ducts and disappearance of the distal part of the excretory duct from the dorsal bud. The ventral bud excretory duct then drains the entire pancreas and takes the name of the main pancreatic duct. In approximately 10% of cases, the excretory duct of the dorsal bud persists and gives an accessory excretory route, the accessory pancreatic duct which opens into the duodenum at the level of the minor duodenal papilla, upstream of the main papilla. Due to the rotations of the stomach and the significant development of the liver, there is adjoining of the mesoduodenum to the posterior wall of the abdomen then fusion with the peritoneum. The pancreas thus secondarily becomes a partially retroperitoneal organ.