بسم الله الرحمن الرحيم

Development of GIT Foregut Development

Introduction Origin: Endoderm of gut (except mouth and lower half of anal canal which are ectodermal)  mucosa & its glands. Splachnic secondary mesoderm  smooth muscles and connective tissue. GIT is formed from the incorporation of the dorsal part of yolk sac into the embryo due to head, tail and lateral folds.

Development of the primitive gut tube It extents from the oral membrane to the cloacal membrane. It is divided into: 1-Foregut: from pharynx to the middle of 2nd part of duodenum. 2-Midgut : from lower half of 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.

Derivatives of the gut Foregut Midgut Hindgut Pharynx Oesophagus Stomach 1st and half of 2nd parts of duodenum Liver and gall bladder Pancreas Respiratory system Half of 2nd , 3rd and 4th parts of duodenum Jujenum Ileum Appendix Caecum Ascending colon Right colic flexure Right 2/3 of transverse colon. Left 1/3 of transverse colon. Left colic flexure. Descending colon. Segmoid colon. Rectum. Upper ½ of anal canal. Primitive urogenital sinus derivatives.

Development of the oesophagus At 4 weeks old a respiratory diverticulum appears at the ventral wall of the foregut. The trachea develops from its ventral border. The esophagus develops from its posterior part. They are comunicating then a tracheaoesophageal septum develops between them.

1- Endoderm of foregut -----mucosa & its glands 1- Endoderm of foregut -----mucosa & its glands. 2- Splanchynic secondary mesoderm ---submucosa & musculosa. 3- Mesenchyme of branchial arches striated muscles of upper 1/3 of oesophagus.

The oesophagus is first short then elongates The oesophagus is first short then elongates. Epithelium of oesophagus proliferates, obliterating the lumen then recanalization occurs.

Congenital anomalies of Esophagus 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. Oesophageal atresia: Due to failure of recanalization. 4. Oesophageal stenosis: Due to incomplete recanalization.

Development of the Stomach Appears as a fusiform dilation of the foregut (4 week). It rotates 90 degrees clockwise around a longitudinal axis so: - left side becomes the anterior surface and the right side becomes the posterior surface. - left vagus becomes anterior gastric nerve & right vagus becomes posterior gastric nerve. Figure is from Langman’s Embryology

Later, the appearance and position change due to differential growth and change in surrounding organs as follows:. 1-The left margin grows faster than the right resulting in the formation of the greater and lesser curvatures. 2- The pyloric end moves to the right and the cardiac end moves to the left due to development of the liver (the stomach becomes oblique).

Congenital anomalies of the stomach Thoracic stomach: associated with short oesophagus. Congenital pyloric stenosis: due to hypertrophy of circular muscles in the pyloric region  projectile vomiting of the infant after feeding. Hourglass stomach. Transposition of stomach ( may be associated with situs inversus).

Congenital anomalies of the duodenum 1- Duodenal atresia: due to non canalization. 2- Duodenal stenosis: due to partial canalization. 3- Congenital intestinal obstruction: due to traction of Treitz ligament on the duodenojejunal junction. 4- Duplication of the duodenum: due to abnormal recanalization.

Development of the liver •Hepatic bud develops from the ventral border of duodenum (foregut). •It divides into pars hepatica and pars cystica. Pars cystica undergoes canalization and gives gall bladder and cystic duct. Development of the liver

• Pars hepatica divides into right and left branches which arrange in solid cords. These cords invade septum transversum giving liver cells and epithelial lining of bile canaliculi, hepatic ducts and common hepatic duct. • Septum transversum gives the liver capsule, forms the stroma, the falciform ligament, lesser omentum and the blood forming or hematopoietic tissue (Kupffer cells) of the liver.

Congenital anomalies: 1- Increased lobulation of liver. 2- Absence of gall bladder and cystic duct: It is due to failure of development of pars cystica. 3- Double gall bladder and cystic duct: It is due to development of two separate gall bladders connected by a single cystic duct or by separate ducts. 4- Atresia of common bile duct: It is due to failure of canalization of biliary passage and associated with jaundice after birth. 5- Atresia of gall bladder. 6- Congenital choledochal cyst: It is a dilated part of common bile duct due to weakness of the wall of this part.

Development of the Pancreas • The pancreas develops from dorsal and ventral pancreatic buds that arise from the endoderm of the duodenum. • The dorsal pancreatic bud grows more rapidly than the ventral and soon extends dorsally behind the duodenum.

The duodenum grows and rotates to the right (clockwise) and carries the ventral pancreatic bud dorsally where it fuses with the dorsal bud during the seventh week. •The dorsal bud forms the body and tail of the pancreas. •Ventral bud forms the uncinate process and most of the head of the pancreas.

The main pancreatic duct is formed by union of distal part of the duct of the dorsal bud with the duct of the ventral bud and the communication in between. - The accessory pancreatic duct is formed from the proximal part of the duct of the dorsal bud. - Each solid duct gives branches (ductules) which gives solid cell masses connected to the duct system (acini) and solid cell masses without connection to duct system (Islets of Langerhans). - The connective tissue of the gland develops from the splanchnic mesoderm. - By the fifth month, insulin secretion begins.

Congenital anomalies 1- Annular pancreas: The part of the ventral pancreatic bud rotates towards the left in front of the duodenum. Hence, the pancreatic tissue surrounds the duodenum, it obstructs the duodenum.

2- Accessory or ectopic pancreatic tissue: It lies frequently in the mucosa of the stomach and Meckel’s diverticulum. 3- Absence of dorsal or ventral pancreas. 3- Separate ducts.

Thank You Prof.: Dr. Shawky Tayel