1.THE FOREGUT For descriptive purposes the primordial gut is divided into four parts: 1.Pharyngeal gut 2.Foregut 3.Midgut 4.Hindgut.

2. Lateral view of developing 26 day old embryo showing different parts of primitive gut. Foregut begins caudal to respiratory diverticulum and extends up to liver diverticulum. 3. The derivatives of the foregut are: Esophagus Stomach Duodenum, proximal to the opening of the bile duct Liver, biliary apparatus (hepatic ducts, gallbladder, and bile duct) Pancreas 4. Foregut ends at the level of liver diverticulum. Midgut begins caudal to foregut. This junction where the foregut ends and midgut begins is called anterior intestinal portal. The midgut extends from anterior intestinal portal to posterior intestinal portal. 5. Let us first understand intestinal portal 6. Derivatives of midgut Small intestine, including most of the duodenum Cecum, vermiform appendix, ascending colon, and right half to two-third of transverse colon. All these derivatives are supplied by superior mesenteric artery, the artery of the midgut. Similarly derivatives of midgut are drained by superior mesenteric vein. 7. The small intestine is the longest section of the digestive tube It is about seven meters long It is a tunnel from the pylorus to the large intestine It is divided into three segments: duodenum, jejunum and ileum 8. Duodenum is the first part of small intestine. So it is the widest part of small intestine. It is C shaped structure. It is only 25 cm long. t lacks mesentery. It is retroperitoneal and fixed to posterior abdominal wall. 9. Duodenum becomes jejunum opposite the second lumbar vertebra. At duodenojejunal junction it turns abruptly anteriorly forming duodenojejunal flexure. 10. Duodenum receives secretions from Liver via common bile duct pancreas through pancreatic duct 11. Duodenum is divided into four portions: First or Superior part Second or Descending part Third or Horizontal part Fourth or Ascending part 12. The first (superior) part begins as a continuation of the duodenal end of the pylorus. From here it passes laterally (right), superiorly and posteriorly, for approximately 5 cm, before making a sharp curve inferiorly into the superior duodenal flexure (the end of the superior part). It is the only intraperitoneal portion of the duodenum 13. The second or descending part The second (descending) part of the duodenum begins at the superior duodenal flexure. It passes inferiorly to the lower border of vertebral body L3, before making a sharp turn medially into the inferior duodenal flexure (the end of the descending part). 14. Inferior or horizontal part The third (inferior/horizontal) part of the duodenum begins at the inferior duodenal flexure and passes transversely to the left, crossing the right ureter, right testicular/ovarian vessels, inferior vena cava, abdominal aorta and the vertebral column 15. Ascending part The fourth (ascending) part passes superiorly, either anterior to, or to the left of, the aorta, until it reaches the inferior border of the body of the pancreas. Then, it curves anteriorly and terminates at the duodenojejunal flexure where it joins the jejunum. 16. The duodenum Its fourth part lies anterior to the IVC It is shortest, narrowest and most sessile part of small intestine It is 30 cm long It encircles the umbilicus It has superior and inferior duodenal flexures 17. Its fourth part lies anterior to and left of the abdominal aorta It is shortest, widest and most sessile part of small intestine It is 20-25 cm long It is situated entirely above the level of umbilicus It has superior and inferior duodenal flexures 18. The wall of small intestine consists of four classical coats Mucosa Submucosa Muscularis Serosa 19. Identification points Lining epithelium is simple columnar with goblet cells Intestinal villi are numerous They are tall and broad They are mucosal projections with a core of lamina propria They are covered by simple columnar epithelium with goblet cells 20. The intestinal glands or crypts of Lieberkhn are lined by simple columnar epithelium containing goblet cells and paneth cells Paneth cells are present at the bases of the glands and they are most numerous in duodenum 21. Plicae circulares or circular folds or Kerckrings valves are present They are submucosal horizontal or transverse semilunar folds or valves, containing mucosa and submucosa Brunners glands are present in submucosa and mucosa. They are compound tubular mucous secreting glands 22. Development of the Duodenum 23. Duodenum begins to develop in the early part of fourth week. It (epithelium) develops from caudal part of foregut and cranial part of midgut. All the other layers of duodenum are derived from surrounding splanchnic mesenchyme. The junction of the two parts of the duodenum is just distal to the origin of the liver diverticulum and in adult it is common bile duct. At this junction the ventral and dorsal pancreatic buds are also developing. 24. Duodenum grows rapidly, forming a C-shaped loop ventrally. 25. As stomach rotates 90 degrees in clockwise direction around its longitudinal axis to the left, duodenal loop rotates to the right. This rotation together with rapid growth of pancreas swings duodenum from its initial midline position to the right. 26. Duodenum and pancreas are pressed against posterior abdominal wall. The right leaf of dorsal meso-duodenum fuses with parietal layer of peritoneum. The two layers subsequently disappear. Duodenum and pancreas become retroperitoneal structures. Mesoduodenum disappears entirely except in the region of pylorus of stomach, where a small portion of duodenum (duodenal cap) retains its mesentery and remains intraperitoneal. 27. Transverse sections 5th and 7th week embryo 28. During the fifth and sixth weeks, the lumen of duodenum becomes progressively smaller and is temporarily obliterated because of the proliferation of its epithelial cells. Normally vacuolization occurs because of degeneration of the epithelial cells. As a result, the duodenum normally becomes re-canalized by the end of the embryonic period. But sometimes the occlusion persists leading to duodenal stenosis. 29. Because duodenum is developing from foregut and midgut, it is supplied by branches of celiac and superior mesenteric arteries. 1.right gastric - a branch of hepatic artery - a branch of celiac trunk. 2.supra-duodenal arises from either gastro- duodenal, hepatic artery, or right gastric artery. Gastro-duodenal and right gastric are branches of hepatic artery. Hepatic artery is branch of celiac trunk. 30. 1. right gastro-epiploic - a branch of hepatic artery - a branch of celiac trunk. 2. superior pancreatico-duodenal - a branch of hepatic artery - a branch of celiac trunk. 3. inferior pancreatico-duodenal a branch of superior mesenteric artery.