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Development of foregut

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Development of foregut

  2. 2. Introduction • Development of alimentary tract: Alimentary tract develops from the primitive gut. • Primitive gut is formed due to incorporation of dorsal part of definitive yolk sac within the embryo when the embryo gets folded on itself at the caudal and cranial ends and also due to lateral folding • It communicates with • Yolk sac through the vitellointestinal duct. • Allantoic diverticulum. • It is closed anteriorly by buccopharyngeal membrane which separates it from stomodeum Posteriorly it is closed by cloacal membrane which separates it from proctodeum. 2
  3. 3. Introduction Primitive gut has 3 parts: • Foregut : Cranial part of the gut that lies in the head fold • Midgut: Part of gut that communicates with vitellointestinal duct • Hindgut: Caudal part of gut that lies in the tail fold • Anterior intestinal portal: Communication between foregut and midgut • Posterior intestinal portal: Communication between midgut and hindgut. • Vitellointestinal duct disappears by 5th week 3
  4. 4. Foregut Extent: From the Oral cavity to a point where common bile duct opens into Duodenum Derivatives 1. Pharynx and its derivatives ( oral cavity, pharynx, tongue, tonsils, salivary glands and upper respiratory system 2. The lower respiratory system 3. Oesophagus and stomach 4. Duodenum, proximal to the opening of the bile duct 5. Liver, gallbladder , extrahepatic biliary apparatus 6. Pancreas 4
  5. 5. Midgut Extent: From the opening of bile duct in duodenum to the junction of right 2/3rd and left 1/3rd of transverse colon Derivatives 1. Duodenum beyond the opening of common bile duct 2. Jejunum 3. Ileum 4. Appendix 5. Cecum 6. Ascending colon 7. Right colic flexure 8. Right 2/3 of transverse colon 5
  6. 6. Hindgut Extent: From the junction of right 2/3rd and left 1/3rd of transverse colon to the upper part of anal canal Derivatives 1. Left 1/3 of transverse colon. 2. Left colic flexure. 3. Descending colon. 4. Sigmoid colon. 5. Rectum. 6. Upper ½ of anal canal. 7. Primitive urogenital sinus derivatives. 6
  7. 7. Mesenteries of GIT Gut is attached to body wall by the ventral and dorsal mesenteries. • Ventral Mesentery: Exists only in the terminal part of oesophagus, stomach and upper part of duodenum. Growth of liver divides it into • Lesser omentum • Falciform ligament • Dorsal Mesentery: Suspends the caudal part of foregut, midgut & a major part of the hindgut from the abdominal wall. It forms: • Dorsal mesogastrium • Dorsal mesoduodenum • Dorsal mesentery of jejunal & ileal loops (Mesentery proper) • Dorsal mesocolon 7
  8. 8. Blood supply of GIT • Dorsal to the gut tube lies the Dorsal Aorta. • It gives off a large no of ventral branches called vitelline arteries. Most of these disappear and only 3 remain • Coeliac trunk: supplies the foregut • Superior Mesenteric artery: supplies the midgut • Inferior mesenteric artery: supplies the hindgut . 8
  9. 9. Development of Oesophagus • Develops from the part of foregut between the pharynx and stomach. • Stages of Development • At 4th wk of IUL :Tracheobronchial or respiratory diverticulum appears in the ventral aspect of foregut at the caudal end of pharyngeal foregut. • Soon Tracheoesophageal fold and septum develops which divides it into two parts: ventral trachea and dorsal oesophagus. • Initially oesophagus is short but elongates due to the formation of neck and descent of the diaphragm, lungs and heart. 9
  10. 10. Histogenesis of Oesophagus • Endoderm of foregut: Forms the Epithelium & gland • Splanchnopleuric mesoderm surrounding the foregut: Forms the muscles and connective tissue • Muscular coat of oesophagus is made up of • Striated muscles in upper 1/3 • Mixed coat in middle 1/3 • Smooth muscles in lower 1/3 10
  11. 11. Anomalies of Oesophagus • Oesophageal atresia: due to deviation of tracheooesophageal septum in a posterior direction or Failure of recanalisation of the oesophagus. • Oesophageal stenosis: Due to incomplete recanalization of oesophagus. Polyhydramnios • Tracheoesophageal fistula: Communication of trachea with oesophagus • Achalasia cardia or cardiospasm: Failure of muscular relaxation in lower part of oesophagus due to loss of ganglionic cells in Auerbach’s plexus. 11
  12. 12. Development of Stomach • Stomach develops during 4th–5th week as a fusiform dilatation of the part of the foregut distal to the oesophagus. • Fusiform sac has left and right surfaces and ventral and dorsal borders. • Due to differential growth, Dorsal border grows more. • It forms the fundus and greater curvature of stomach. • Ventral border grows slowly and forms lesser curvature. 12
  13. 13. • Rotation of stomach takes place in a clockwise direction (around 90°) both along the longitudinal axis & transverse axis • Rotation along longitudinal axis : Left surface becomes the anterior surface and the Right surface becomes the posterior surface. • This explains why the anterior surface is supplied by left vagus nerve and posterior surface by right vagus. • Rotation along anteroposterior axis : Lower or pyloric end faces upwards and to the right. Upper or cardiac end faces downwards and to the left. Rotation of Stomach 13
  14. 14. Mesenteries of Stomach • Ventral mesogastrium : attached to the ventral border, attaches it to septum transversum • Dorsal mesogastrium : attached to dorsal border, attaches it to dorsal body wall Liver develops in ventral mesogastrium & divides it into • Lesser omentum : Between liver and stomach • Falciform ligament : Between liver and anterior abdominal wall Spleen develops in dorsal mesogastrium & divides it into • Gastrosplenic ligament: Between greater curvature of the stomach (fundus) and spleen • Lienorenal ligament : Between spleen & posterior body wall 14
  15. 15. Formation of Lesser sac (Omental bursa) • Omental bursa is a space behind the stomach • It is formed when dorsal mesogastrium is pulled to the left as a result of rotation of stomach around longitudinal axis. 15
  16. 16. Formation of Greater Omentum • The dorsal mesogastrium from rest of the greater curvature extends downwards to form a double layered fold of peritoneum called Greater omentum. 16
  17. 17. Anomalies of Stomach • Congenital Hypertrophic Pyloric Stenosis: Hypertrophy of circular muscle layer at pylorus More common in males Characterized by progressive vomiting Treatment: Surgical correction. • Duplication of Stomach • Presence of prepyloric septum • Thoracic stomach: Oesophagus is short and the stomach is displaced in the thorax through the oesophageal opening 17
  18. 18. Development of Duodenum Duodenum develops from two sources: • 1st part & 2nd part up to the opening of CBD: Foregut (Supplied by branches of Coeliac trunk) • 2nd part beyond opening of CBD, 3rd & 4th part: Midgut (Supplied by branches of Superior Mesenteric artery) • Duodenum is attached to the dorsal body wall by mesoduodenum 18
  19. 19. • Primitive duodenum is in the form of a loop with a ventral convexity in the median plane. It is attached to the posterior abdominal wall by mesoduodenum • When the stomach rotates , the duodenal loop rotates to the right and the mesoduodenum fuses with the peritoneum of posterior abdominal wall. Later both of them disappear. • By the end of the embryonic period duodenum becomes retroperitoneal except near pylorus of stomach where a small portion of duodenum remains intraperitoneal ( duodenal cap) Development of Duodenum 19
  20. 20. Anomalies of Duodenum • Duodenal atresia: Complete occlusion of lumen. Produces polyhydramnios. • Duodenal stenosis: Partial occlusion Bile stained vomiting • Duodenal diverticula: usually arises from the second part of the duodenum. 20
  21. 21. • Liver develops from the following sources: • Endodermal liver bud forms the hepatocytes and intrahepatic biliary apparatus. • Septum transversum forms connective tissue of liver including fibrous capsule, Kupffer’s cells and blood vessels. • Vitelline and umbilical veins form sinusoids. • Ventral mesentery forms lesser omentum , falciform, coronary and triangular ligaments. Development of Liver 21
  22. 22. Development of Liver Stages of development • Formation of hepatic bud: During the 5th week of IUL, hepatic bud arises from terminal part of foregut. • It grows in ventral mesogastrium and divides into cranial pars hepatica and smaller caudal pars cystica. • The pars hepatica reaches the septum transversum and divides into right and left hepatic branches • Each hepatic branch forms solid cord of cells called hepatic trabeculae which form the two lobes of liver 22
  23. 23. Development of Liver • The hepatic trabeculae differentiate into solid plates of liver cells which form liver parenchyma and lining of biliary canaliculi • The vitelline and umbilical veins lying in the septum transversum break up into a capillary network and form Hepatic sinusoids • The mesenchyme of the septum transversum form Haematopoietic cells Kupffer’s cells Connective tissue cells Blood vessels Capsule of the liver 23
  24. 24. Development of Gallbladder & Biliary Apparatus • Gall bladder and cystic duct develops from Cystic bud • The right and left branches of the pars hepatica become canalized to form the right and left hepatic ducts • The hepatic ducts join to form Common hepatic duct • The common hepatic duct and cystic duct join to form Common bile duct. • Extrahepatic biliary apparatus is endodermal in origin • Differential growth of duodenal wall pushes the opening of common bile duct form ventral aspect to dorsomedial aspect of duodenum along with ventral pancreatic bud. 24
  25. 25. Anomalies of Gallbladder • Agenesis of gallbladder • Sessile gallbladder : Absence of cystic duct • Phrygian cap: Fundus is folded on itself to form cap-like structure. • Hartmann’s pouch: Outpouching of the neck of the gallbladder. • Intra-hepatic gallbladder: Gallbladder is embedded in the substance of the liver. 25
  26. 26. • Septate gallbladder: The lumen of the gallbladder is divided into several segments with partial septae. • Double gallbladder: Two gallbladders are present that are connected with the cystic duct. • Floating gallbladder: Gallbladder is lined by peritoneum on both the surfaces and is free from the liver. Anomalies of Gallbladder 26
  27. 27. Anomalies of Extrahepatic Biliary Ducts • Atresia of ducts: The ducts of the extra- hepatic biliary apparatus may be partially or completely absent. • Accessory ducts: Small accessory bile duct connecting the liver with the gallbladder may be present. 27
  28. 28. Development of Pancreas • Pancreas develops from two endodermal buds: • Dorsal bud : larger, located in dorsal mesentery • Arises from the dorsal aspect of duodenum and gives rise to upper part of the head, neck, body and tail • Ventral bud : smaller, located in ventral mesentery Arises from the hepatic diverticulum and gives rise to lower part of head and uncinate process. • Due to rotation and differential growth of walls of duodenum the ventral bud moves to right and comes to lie below and behind the dorsal bud. • Both the buds fuse in 7th wk of IUL 28
  29. 29. • Formation of acini and islet of Langerhans: • The proliferation of both the ventral and dorsal pancreatic ducts form smaller ductules • At the end of each branch, pancreatic acini appear. Some cells of the acini get separated and form islet of Langerhans in 3rd month and start secretion of insulin by 5th month. • Glucagon and Somatostatin secreting cells also develop from parenchymal cells • Surrounding splanchnic mesoderm condenses to form capsule, connective tissue, septa and blood vessels of the pancreas. Development of Pancreas 29
  30. 30. Formation of pancreatic ducts • Main pancreatic duct ( Duct of Wirsung ) : 3 sources Distal part of duct of dorsal pancreatic bud Oblique communication between duct of dorsal and ventral buds Duct of ventral pancreatic bud. Opens at major duodenal papilla. • Accessory pancreatic duct ( Duct of Santorini ): Proximal part of duct of dorsal pancreatic bud. Opens at minor duodenal papilla Development of Pancreatic duct system 30
  31. 31. Anomalies of Pancreas • Annular pancreas : Second part of duodenum is surrounded by a ring of pancreatic tissue. • Divided pancreas: Due to failure of fusion of the dorsal and ventral pancreatic buds. • Inversion of pancreatic duct: The main pancreatic duct is formed by the duct of dorsal pancreatic bud and opens at minor duodenal papilla, whereas the duct of ventral pancreatic bud joins the common bile duct and opens at major duodenal papilla. • Accessory pancreatic tissue: ectopic pancreatic tissue that lies in the wall of duodenum, gallbladder, Meckel’s diverticulum or stomach 31
  32. 32. Development of Spleen • During the 5th week of IUL, mesenchymal cells in the dorsal mesogastrium form small masses called spleniculi or splenic lobules. • Spleniculi fuse to form a single mass which projects to the left and is covered by peritoneum • The dorsal mesogastrium is divided by the developing spleen into the ventral gastrosplenic ligament and dorsal lienorenal ligament. • Capsule, septa, connective tissue framework, lymphocytes & haemotopoietic cells are all derived from mesoderm • Lobulated development of spleen in an adult is indicated by splenic notches. 32
  33. 33. • Agenesis • Accessory spleen: Failure of fusion of spleniculi Sites : Hilum of spleen • Gastrosplenic ligament • Lienorenal ligament • Tail of pancreas • Along the splenic artery • Left spermatic cord • Lobulated spleen: Incomplete fusion of spleniculi • Situs inversus Anomalies of Spleen 33
  34. 34. THANK YOU 34