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Embryology of Gastrointestinal Tract( GIT)

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Embryology19 Dr.Ban Embryology of gastrointestinal tract( GIT) Gastrointestinal tract (GIT) arises initially during the process of gastrulation from the endoderm of the trilaminar embryo (week 3) and extends from the buccopharyngeal membrane to the cloacal membrane. The oral cavity (mouth) is formed following breakdown of the buccopharyngeal membrane (oropharyngeal or oral membrane). Human head showing buccopharyngeal membrane breakdown. The tract and associated organs later have contributions from all the germ cell layers.The tube is divided into 3 distinct sections; foregut ,midgut , hindgut. Foregut gives rise to the esophagus, stomach, liver, gallbladder, bile ducts, pancreas and proximal duodenum. The midgut develops into the distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and proximal 2/3rd of transverse colon. The hindgut becomes the distal 1/3rd of the transverse colon, descending colon, sigmoide Embryonic cephalocaudal and lateral folding The Primitive gut tube develops during week 3-4 during craniocaudal and lateral folding of the embryo.The process of cephalocaudal and lateral folding transforms the embryo from a flat disc to a three-dimensional vertebrate body 1 Embryology19 Dr.Ban form. As folding occurs, the embryo grows more rapidly than the yolk sac, the cavity of which remains continuous with the developing gut tube through the narrowing vitelline duct.(The large mid-gut is generated by lateral embryonic folding which "pinches off" a pocket of the yolk sac). Foregut Esophagus: Since the upper part of the foregut is divided by the tracheoesophageal septum into the esophagus posteriorly and the trachea and lung buds anteriorly. 2 Embryology19 Dr.Ban The tracheoesophageal septum divides the foregut into the esophagus and trachea. Stomach: The primordium of the primitive stomach is visible about the end of the 4th week. It is initially oriented in the median plane and suspended from the dorsal wall of the abdominal cavity by the dorsal mesentery or mesogastrium. During development the stomach rotates (90° ) in a clockwise direction along its longitudinal axis, placing the left vagus nerve along its anterior side and the right vagus nerve along its posterior side. Rotation of the stomach creates the omental bursa or lesser peritoneal sac. The lesser sac, also known as the omental bursa, is the cavity in the abdomen that is formed by the lesser and greater omentum.The omentum. It's a curtain of fatty tissue that hangs down from our stomach and liver and wraps around the intestines. Duodenum: The duodenum acquires its C-shaped loop as the stomach rotates. Because of its location at the junction of the foregut and the midgut .Branches of both the celiac trunk and the superior mesenteric artery supply the duodenum. 3 Embryology19 Dr.Ban Pancreas: The pancreas develops from two outgrowths of the endodermal epithelium, the dorsal pancreatic bud and the ventral pancreatic bud. During rotation of the gut these primordial come together to form a single pancreas. The ventral pancreatic bud forms the uncinate process and part of the head, while the dorsal pancreatic bud forms the remainder of the head, body, and tail of the pancreas. 4 Embryology19 Dr.Ban Liver: The liver develops from endodermal cells that form the hepatic diverticulum. The liver grows in close association with the septum transversum, which later forms part of the diaphragm. As it grows the hepatic diverticulum divides into a cranial part, which forms the parenchyma of the liver, and the caudal part, which gives rise to the gallbladder and cystic duct. The embryonic liver is large and fills much of the abdominal cavity during the 7th through 9th weeks of development.Blood formation (hemopoiesis) begins in the liver during the 6th week of development, and bile formation begins in the 12th week. 5 Embryology19 Dr.Ban Spleen: The spleen develops from mesenchymal cells located between layers of the dorsal mesogastrium,it is located on the left side of the abdomen and has a role initially in blood and then immune system development. The spleen's haematopoietic function (blood cell formation) is lost with embryo development and lymphoid precursor cells migrate into the developing organ. 6 Embryology19 Dr.Ban 7 .
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