Development of foregut


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Development of foregut

  1. 1. Development of the GIT MOHAMED ELADL
  2. 2. OBJECTIVES After completion of this session, the students should be able to 1. Relate embryonic enfolding to the formation of the primary gut tube. 2. List the parts of the primary gut tube. 3. Define the position and extent of dorsal and ventral mesenteries. 4. Describe the formation of the esophagus and lung bud. 5. Describe the rotation of the stomach. 6. Describe the formation of the Omental bursa. Pancreas. Greater omentum. 7. List the derivates of the ventral mesogastrium. 8. Discuss the rotation and recanalization of the duodenum. 9. Illustrate the formation of the primary intestinal loop. 10. Understand the formation of the physiological umbilical hernia. 11. Describe the rotation, coiling of the midgut, & retraction of herniated loops. 12. Outline the development of the cecum. 13. List the derivatives of the hindgut and cloaca. 14. Recognize the dual origin of the anal canal. 15. Congenital anomalies of the GIT development Dr M Eladl
  3. 3. DEVELOPMENT OF THE GIT  The primitive gut is formed by incorporation of yolk sac during foldings 1. Closed at its cranial end by the oropharyngeal membrane that breaks down at the stomodeum. 2. Closed at its caudal end by the cloacal membrane that breaks down at the proctodeum. Dr M Eladl
  4. 4. DEVELOPMENT OF THE GIT  The digestive tract is divided based on vascular supply into 1. Foregut: Coeliac trunk 2. Midgut: Superior Mesenteric A 3. Hindgut: Inferior Mesenteric A Dr M Eladl
  5. 5. VENTRAL AND DORSAL MESENTERIES AND THEIR FATES 1. Ventral mesentery: - Exists only in the region of the terminal part of the esophagus, the stomach, and the upper part of the duodenum. - Derived from septum transversum. - Growth of the liver divides the ventral mesentery into: - lesser omentum. - falciform ligament. Dr M Eladl
  6. 6. VENTRAL AND DORSAL MESENTERIES AND THEIR FATES 2. Dorsal mesentery: - Suspends the caudal part of the foregut, the midgut, and a major part of the hindgut from the abdominal wall. - Forms - Dorsal mesogastrium - Dorsal mesoduodenum - Dorsal mesentery of the jejunal and ileal loops forms the mesentery proper. - Dorsal mesocolon Dr M Eladl
  7. 7. VENTRAL AND DORSAL MESENTERIES AND THEIR FATES The Dorsal mesogastrium: - Most of it forms the greater omentum - The dorsal mesogastrium between the stomach and spleen becomes the gastrosplenic ligament and the part between the spleen and kidney becomes the lienorenal (splenorenal) ligament. - The spleen remains intraperitoneal Dr M Eladl
  8. 8. 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), and pancreas.  The coeliac trunk supplies all these derivatives except: – Pharynx – Most of the oesophagus. – Respiratory tract Dr M Eladl
  9. 9. DEVELOPMENT OF THE ESOPHAGUS 1. Division of the cranial part of the foregut immediately caudal to the primitive pharynx to: Trachea (anterior) & Esophagus (posterior). 2. Initially, the esophagus is short. 3. 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. Recanalization of the lumen occurs by the end of the embryonic period. Dr M Eladl
  10. 10. DEVELOPMENT OF THE ESOPHAGUS Dr M Eladl 6. The epithelium and glands are derived from endoderm. 7. The striated muscle in the upper 2/3 of the oesophagus and the smooth muscles of the lower 2/3 is derived from the mesoderm.
  11. 11. ANOMALIES OF THE OESOPHAGUS 1. Esophageal atresia:  DUE TO deviation of the tracheo- esophageal septum in a posterior direction OR failure of recanalization of the oesophagus.  Features: – Associated with tracheoesophageal fistula: There is incomplete separation of the esophagus from the laryngo – tracheal tube. – Associated prematurity (about 1/3). – A fetus is unable to swallow the amniotic fluid. This results in polyhydramnios. Dr M Eladl
  12. 12. ANOMALIES OF THE OESOPHAGUS 3. Short oesophagus & congenital hiatal hernia:  The oesophagus fails to elongate so it is very short and may be associated with thoracic stomach. Dr M Eladl 2. Esophageal stenosis:  Due to incomplete recanalization of oesophagus.
  13. 13. DEVELOPMENT OF THE STOMACH  Around the middle of the 4th week.  Develops from the distal part of the foregut.  It is initially a simple tube. Dr M Eladl
  14. 14. DEVELOPMENT OF THE STOMACH  Slight dilatation in the stomach occurs and the stomach becomes fusiform in shape.  The posterior border grows faster than its anterior border. This result in the anterior border becomes the lesser curvature & the posterior border becomes the greater curvature. Dr M Eladl
  15. 15. ROTATION OF THE STOMACH  Rotation is due to: – Differential growth of the stomach. – Growth of the liver. Dr M Eladl  Rotation of the stomach 90 degree in a clockwise direction around both the longitudinal and transverse axes of the stomach:
  16. 16. RESULTS OF ROTATION OF THE STOMACH  Around its longitudinal axis: – The anterior border (lesser curvature): becomes right – The posterior border (greater curvature) becomes left. – The left side becomes anterior surface. – The right side becomes posterior surface. Dr M Eladl
  17. 17. RESULTS OF ROTATION OF THE STOMACH  Around its transverse axis: – Before rotation:  The cranial & caudal ends of the stomach are in the median plane. – After rotation:  The cranial end moves to the left and slightly inferiorly, and its caudal end moves to the right and superiorly.  The long axis of the stomach becomes transverse to the long axis of the body. Dr M Eladl
  18. 18. RESULTS OF ROTATION OF THE STOMACH The rotation explains why the left vagus nerve supplies the anterior wall of the adult stomach and the right vagus nerve innervates its posterior wall. Dr M Eladl
  19. 19. DEVELOPMENT OF OMENTAL BURSA  The lesser sac of peritoneum: Rotation of the stomach is thought to pull the dorsal mesogastrium to the left and the lesser sac becomes expanded transversely between the stomach and the posterior abdominal wall. Dr M Eladl
  20. 20. ANOMALIES OF THE STOMACH  Congenital hypertrophic pyloric stenosis: – The circular muscles in the pyloric region are hypertrophy. This result in stenosis of the pyloric canal. Dr M Eladl
  21. 21. ANOMALIES OF THE STOMACH  Thoracic stomach: – Due to the short oesophagus, the stomach is displaced superiorly through the esophageal opening Dr M Eladl
  22. 22. ANOMALIES OF THE STOMACH  Hour-glass stomach: – A constriction in the middle of the stomach divided it into two dilated portions. – It occurs in adults due to chronic peptic ulceration there is fibrosis and contracture of the stomach leading to an hourglass shape as well as altered mobility Dr M Eladl
  23. 23. ANOMALIES OF THE STOMACH  Transposition of the stomach to the right side: – Due to rotation 90 degree in an opposite direction. – The lesser curvature moves to the left and the greater curvature moves to the right. – The left vagus nerve supplies the posterior wall of the stomach and the right vagus nerve innervates it anterior wall. Dr M Eladl
  24. 24. DEVELOPMENT OF THE DUODENUM  In the 4th week.  Begins to develop from the endoderm of the caudal part of the foregut and the cranial part of the midgut.  The developing duodenum grows rapidly, forming a C- shaped loop that projects ventrally. Dr M Eladl
  25. 25. DEVELOPMENT OF THE DUODENUM  The duodenum is attached to the posterior abdominal wall by dorsal mesoduodenum and with the liver and anterior abdominal wall by ventral mesoduodenum. Dr M Eladl
  26. 26. DEVELOPMENT OF THE DUODENUM  As the stomach rotates, the duodenal loop rotates to the right and the dorsal mesoduodenum fuses with the peritoneum of the posterior abdominal wall and both disappear.  By the end of the embryonic period, most of the ventral mesoduodenum has disappeared.  The lumen of the duodenum becomes obliterated because of the proliferation of its epithelial cells.  Latter recanalization occurs. Dr M Eladl
  27. 27. BLOOD SUPPLY OF THE DUODENUM  The duodenum is supplied by branches of the celiac and superior mesenteric arteries because of its derivation from the foregut and midgut. Dr M Eladl
  28. 28. ANOMALIES OF THE DUODENUM  Duodenal stenosis: – Due to incomplete recanalization of the duodenum.  Duodenal atresia: – Due to failure of recanalization of the duodenum. – Polyhydramnios also occurs because duodenal atresia prevents normal absorption of amniotic fluid by the intestine. Dr M Eladl
  29. 29. DEVELOPMENT OF LIVER & BILIARY PASSAGES  In the 4th week.  The liver arises as a ventral diverticulum from the caudal part of the foregut. This hepatic diverticulum (liver bud) extends into the septum transversum (mass of splanchnic mesoderm between the developing heart and midgut). Dr M Eladl
  30. 30. DEVELOPMENT OF LIVER & BILIARY PASSAGES  The hepatic diverticulum enlarges rapidly and divides into two parts as it grows between the layers of the ventral mesentery Dr M Eladl
  31. 31. PARS HEPATICA  It is the larger cranial part of the hepatic diverticulum.  Gives rise to: – Hepatic cells: – Hepatic sinusoids: – Kupffer cells & hematopoietic tissue.  The liver grow rapidly to fill a large part of the abdominal cavity.  At first, the 2 lobes are of the same size but soon the right become larger.  Bile formation start during the 12th week. Dr M Eladl
  32. 32. PARS CYSTICA  Becomes the gall bladder and the stem of the diverticulum forms the cystic duct.  The stalk connecting the hepatic and cystic ducts to the duodenum becomes the common bile duct.  The right and left branches of the pars hepatica become canalized to form the right and left hepatic ducts. Dr M Eladl
  33. 33. FORMATION OF THE CAPSULE AND LIGAMENTS OF THE LIVER:  As the septum transversum is penetrated by the growing pars hepatica. – The mesoderm of the septum transversum between the liver and the anterior abdominal wall becomes the FALCIFORM LIGAMENT. – The mesoderm of the septum transversum between the liver and the foregut (stomach and duodenum); form the LESSER OMENTUM. – The mesoderm on the surface of the liver differentiates into CAPSULE AND PERITONEAL COVERING Dr M Eladl
  34. 34. SIZE & WEIGHT OF THE LIVER  The liver is large in fetal life (about 10% of total body weight at the 10th week) due to: – Large blood sinusoids. – It is the main hemopoietic organ forming the blood cells, which begins during the 6th week.  The liver weight at birth is only 5% of total body weight. Dr M Eladl
  35. 35. BLOOD SUPPLY OF THE LIVER  Derived from the coeliac trunk, which is the artery of the foregut. Dr M Eladl
  36. 36. DEVELOPMENT OF THE PANCREAS  The pancreas develops from two buds: – Ventral bud: Arises from the hepatic diverticulum and gives the lower part of the head & uncinate process. – Dorsal bud: Arises from the dorsal aspect of the duodenum and gives the upper part of the head, neck, body & tail. Dr M Eladl
  37. 37. DEVELOPMENT OF THE PANCREAS  Rotation of the duodenum & unequal growth of its walls leads to: The ventral pancreas comes to lie below & to the right of the dorsal pancreas, Which latter fuse with each other as will as their ducts. Dr M Eladl
  38. 38. DEVELOPMENT OF THE PANCREAS  Rotation of the duodenum & unequal growth of its walls leads to: The ventral pancreas comes to lie below & to the right of the dorsal pancreas, Which latter fuse with each other as will as their ducts. Dr M Eladl
  39. 39. DEVELOPMENT OF PANCREATIC DUCTS  The main pancreatic duct: From the duct of ventral pancreas (proximally), distal part of the duct of dorsal pancreas (distally).  The accessory pancreatic Duct: From the proximal part of the duct of the dorsal pancreas Dr M Eladl
  40. 40. DEVELOPMENT OF PANCREATIC ACINI & ISLETS  Side branches extend from the ducts to the surrounding mesoderm.  Some of them become canalized  pancreatic Acini.  Others separate & not canalized  Islets of Langerhans.  Insulin secretion begins during the fetal period (10 weeks) and the total pancreatic insulin contents also increase with the fetal age.  The pancreatic connective tissue stroma and interlobar septa: from the splanchnic mesoderm. Dr M Eladl
  41. 41. ANOMALIES OF PANCREAS  Annular pancreas: – Causes:  Growth of a bifid ventral pancreatic bud which fuse with the dorsal bud forming a ring around the duodenum.  Fixation of ventral lobe to duodenum before rotation. – Features:  A thin and flat band of pancreatic tissue surrounding the descending (second) part of the duodenum may cause duodenal obstruction. Dr M Eladl
  42. 42. ANOMALIES OF PANCREAS  Accessory pancreatic tissue: – Is often located in the wall of the stomach, duodenum or in the meckel diveticulum.  Two pancreases: – Due to failure of union between ventral and dorsal pancreas with failure of anastomosis of their ducts.  Absence of a part of pancreas (Small pancreas): – Due to absence of ventral or dorsal pancreas due to failure of development of one of the pancreatic buds. Dr M Eladl
  43. 43. THANK YOU