Gastrointestinal embryology By: BILAL HUSSEIN

Objectives Quick review Embryonic folding Gastroschisis Omphalocele Peritoneum formation Development of esophagus Anomalies of the esophagus Development of the stomach

Quick review

Embryonic folding The process starts at the 4rd week of gestation. It starts from the trilaminar disc which compose of ectoderm, mesoderm and endoderm .

The yolk sac secretes connective tissue called extra embryonic mesoderm which will surround the yolk sac and amniotic cavity. between the lateral plates of mesoderm there is a cavity called intra embryonic coelom which allows the splanchnic and somatic mesoderm to be in contact with extra embryonic mesoderm .

At the 4th week of gestation and during folding the splanchnic and somatic mesoderm fuse. And the folded ends should merge together and this eventually will leads to formation of the umblical cord and obliteration of the vitelline duct . If the merge between the ends fails the small bowel can herniated through it and this called gastroschisis and in this case the intestine will not be covered by the peritoneum .

Around the 6th week of gestation intestine (jejunum and ileum) pulls or herniated out through the umbilical cord *in the 6th week also the vitellien duct obliterate and we have only umbilical cord. Around the 10th or 11th week of gestation the intestine pulls inside, and if it fails to do so we will have omphalocele

Peritoneum formation

dorsomesogastrium

Development of the foregut Derivatives of the foregut are: 1- primitive pharynx and its derivatives (oral cavity, pharynx, tongue, tonsils, salivary glands and upper respiratory system). 2- lower respiratory system. 3- the esophagus and stomach 4- duodenum, proximal to the opening of the bile duct. 5- the liver, biliary apparatus (hepatic ducts, gall bladder, and bile duct).

Development of esophagus 1- division of the cranial part of the foregut immediately caudal to the primitive pharynx to: trachea (anterior) and esophagus (posterior). 2- initially, the esophagus is short. due to the growth and descent of the heart and lungs it elongates. 4- temporary obliteration of the lumen occurs due to proliferation of the epithelium. 5- reconciliation of the lumen occurs by the end of the embryonic period.

Anomalies of the esophagus Esophageal atresia: Due to deviation of the tracheo-esophageal septum in a posterior direction or failure of recanalization of the esophagus. Features: Associated with tracheoesophageal fistula: there is incomplete separation of the esophagus from the laryngo- tracheal tube

Development of stomach A fusiform dilation in the foregut occurring during the 4th week. Develops from distal part of the foregut. The posterior border grows faster than the anterior border, this result in the anterior border becomes lesser curvature and the posterior border becomes the greater curvature . Result of rotation: the anterior part becomes right The posterior part becomes left

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