Development of the Foregut Dr Rania Gabr

OBJECTIVES 1- Identify the results of folding. 2- Identify the derivatives of the gut. 3- Describe the development of the esophagus. 4- Describe the development of the stomach. 5- Identify the congenital anomalies of the esophagus and stomach.

Folding of the embryo leads to : Development of the primitive gut tube: It extends from the oral membrane to the cloacal membrane. It is divided into: 1-foregut: from pharynx to the 2nd part of duodenum. 2-midgut : from 2nd part of duodenum to the junction between medial 2/3 & lateral 1/3 of transverse colon. 3-hindgut: the remaining part of large intestine.

The derivatives of The Foregut are 1- Pharynx 2- The lower respiratory system 3- The esophagus and stomach 4- The duodenum, distal to the opening of the bile duct 5- The liver, biliary apparatus (hepatic ducts, gallbladder, and bile duct), and 6- Pancreas

The derivatives of The Midgut are: 1-Rest of the duodenum 2- Jejunum 3- Ileum 4- Appendix 5- Cecum 6- Ascending colon 7- Right colic flexure 8- Right 2/3 of transverse colon.

The derivatives of The Hindgut are: 1- Left 1/3 of transverse colon. 2- Left colic flexure. 3- Descending colon. 4- Segmoid colon. 5- Rectum. 6- Upper ½ of anal canal. 7- Primitive urogenital sinus derivatives.

Mesenteries Initially, the gut is in contact with the posterior body wall. By 5th week, the connecting tissue (mesenchyme) between the gut and body wall narrows. Thus, caudal part of the foregut, midgut and major part of the hindgut are suspended by the dorsal mesentery. Dorsal mesentery forms: greater omentum, mesoduodenum, mesocolon and mesentery proper.

Mesenteries

Dorsal Mesentery

Ventral Mesentery Ventral mesentery exists only at the lower end of esophagus, stomach and upper part of the duodenum. Ventral mesentery is derived from the septum transversum. The growth of the liver into the septum transversum results in division of the ventral mesentery. The part of the ventral mesentery between the liver and stomach forms the lesser omentum. The part between the liver and anterior abdominal wall forms the Falciform ligament.

Mesenteries

Fixation of various parts of intestines The enlarged colon presses the duodenum & pancreas against the posterior abdominal wall. C & F Most of duodenal mesentery is absorbed, so most of duodenum ( except for about the first 2.5 cm derived from foregut) & pancreas become retroperitoneal. C & F Intestines prior to fixation Intestines after fixation

Development of the Esophagus It develops from the foregut caudal to laryngo-tracheal groove till stomach. Origin: Endoderm of foregut  mucosa & its glands. Splanchnic secondary mesoderm  submucosa & musculosa. Mesenchyme of branchial arches striated muscles of upper 1/3 of oesophagus.

Development of the Esophagus The part of the foregut extending from the buccopharyngeal membrane to the respiratory diverticulum is called the pharyngeal gut (considered with pharyngeal arches). The Remaining part extends from the respiratory diverticulum to the liver bud.

Development of Esophagus The Esophagus: Develops from the foregut between the respiratory diverticulum and the stomach. The muscle wall of the (esophagus) develops from the splanchnic mesoderm (upper 1/3-skeletal, middle 1/3-mixed and lower 1/3-smooth). Esophagus elongates due to the descent of heart and lungs.

Development of the Esophagus: The oesophagus is first short then elongates. The trachea develops from its ventral border. They are comunicating then a tracheaoesophageal septum develops between them. Epithelium of oesophagus proliferates, obliterating the lumen then recanalization occurs.  

Development of Esophagus

Development of Esophagus

Congenital anomalies: 1. Short oesophagus: Due to failure of elongation . It is associated with thoracic stomach. 2.Tracheo-oesophageal fistula: Due to non separation between trachea and oesophagus  milk in lungs pneumonia.  air in stomach  respiratory distress.

3- Esophageal Atresia: Due to failure of recanalization. 4 3- Esophageal Atresia: Due to failure of recanalization. 4. Oesophageal stenosis: Due to incomplete recanalization

Esophageal atresia with tracheoesophageal fistula

Developmet of the Stomach

Origin: Endoderm of foregut mucosa & its glands. Splanchnic secondary mesoderm submucosa, musculosa and serosa. Development: Fusiform part of foregut: 1- Its dorsal border grows more greater curvature. 2- Its dorsal border grows less lesser curvature. 3- Most cranial part of dorsal border grows rapidly fundus.

Final Shape of Stomach

Steps of stomach development It starts at the 5th week by a fusiform dilatation which has: Upper and lower narrow ends. Anterior and posterior borders which are connected to anterior and posterior abdominal walls by ventral and dorsal mesogastrium. Right and left surfaces which are covered with peritoneum. -This is followed by rapid growth of the posterior border to form greater curvature while the anterior border forms lesser curvature.

Liver is formed in the ventral mesentery, the spleen is formed in dorsal mesentery. Rotation of the stomach to the right (clockwise) for 90 degrees. Results of rotation: 1- Lesser curvature is directed to the right, while greater curvature is directed to left. 2- Left surface is directed anteriorly, right surface is directed posteriorly. 3- Formation of a peritoneal sac behind the stomach, called lesser sac.

4- Left & right vagi will be anterior and posterior gastric nerves. 5- Ventral mesogastrium forms the lesser omentum, capsule around liver, falciform ligament and coronary ligaments. 6- Dorsal mesogastrium forms gastrophrenic, gastrosplenic, lienorenal ligaments and greater omentum. N.B. The Stomach is supplied by the artery of foregut which is the Celiac trunk

Congenital Anomalies 1- Pyloric stenosis: Congenital narrowing of pyloric orifice.(SPHINCTER) 2- Hour glass stomach: constriction of stomach dividing it into 2 dilated parts with a narrowing inbetween. 3- Thoracic stomach: Protrusion of upper part of stomach through diaphragm due to short esophagus.(partial or complete) 4- Transposition of stomach: Right sided stomach.( situs inversus)