Histology & Embryology: Development of the Digestive System [MA] 3.02 PDF

HISTOLOGY & EMBRYOLOGY: LE3 | TRANS 02 DEVELOPMENT OF THE DIGESTIVE SYSTEM DR. MIKAELA DEL ROSARIO - PAJO | 11/07/2024 d OUTLINE Table 1. Four Sect...

HISTOLOGY & EMBRYOLOGY: LE3 | TRANS 02 DEVELOPMENT OF THE DIGESTIVE SYSTEM DR. MIKAELA DEL ROSARIO - PAJO | 11/07/2024 d OUTLINE Table 1. Four Sections Of The Gut Tube I. Divisions of the Gut Tube IV. Pancreas Pharyngeal Gut Oropharyngeal membrane to the II. Mesentery A. Pancreatic (Pharynx) respiratory diverticulum III. Foregut Abnormalities Foregut Remainder caudal to the pharyngeal tube A. Esophagus V. Midgut up to liver outgrowth B. Esophageal A. Abnormalities Midgut Caudal to the liver bud up to the Abnormalities VI. Hindgut junction of the right ⅔ and left ⅓ of the C. Stomach A. Abnormalities transverse colon D. Stomach Hindgut Left ⅓ of the transverse colon to the Abnormalities E. Duodenum cloacal membrane F. Liver & Gallbladder G. Molecular Regulation Endoderm H. Liver & Gallbladder ○ Epithelial lining of the digestive tract Abnormalities ○ Parenchyma of glands – hepatocytes and pancreatic cells SUMMARY OF ABBREVIATIONS Visceral Mesoderm ○ Glandular Stroma ○ Muscle, connective tissue, peritoneal components of gut LEGENDS wall ❗ 👩‍⚕️ 📖 🖥 📝 Must know Lecturer Book Presentation Old Trans MOLECULAR REGULATION During the time that the lateral body folds are bringing the two LEARNING OBJECTIVES sides of the tube together At the end of the lecture, the student should be able to: ✔ Explain the process of the formation of the gut tube, as well as Retinoic Acid its divisions; Initiates specification ✔ Explain the important processes involved in the development From the pharynx (little or no RA) to the colon (highest RA) of the digestive system; Expression of transcription factors ✔ Discuss the molecular factors involved in the regulation of the formation and development of the digestive system; and ✔ Relate common clinical conditions with the abnormal events 💡 GOOD TO KNOW: Molecular Regulation Transcription Factors that occurred during development Table 2. Transcription Factors DIVISIONS OF THE GUT TUBE SOX2 Forms the Esophagus and Stomach PDX1 Forms the Duodenum PRIMITIVE GUT CDXC Forms the Small Intestine Cephalocaudal and lateral folding of the embryo CDXA Forms the Large intestine and Rectum Portion of endoderm from gastrulation incorporated in embryo Yolk sac and allantois remain outside Forms a BLIND ENDING TUBE FOREGUT Cephalic Part HINDGUT Caudal Part [PPT] Figure 2. Molecular Regulators Sonic Hedgehog (SHH) Initiates epithelial-mesenchymal interaction ○ Stabilizes initial patterning Upregulates mesodermal factors that determine the type of structure that forms from the tube HOX genes - components of the mid- and hindgut regions [PPT] Figure 1. Embryo at the end of the 1st month VITELLINE DUCT or YOLK STALK ○ Connection between the MIDGUT and the yolk sac LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 1 of 10  Toldt Fascia Between Visceral Peritoneum and Parietal Peritoneum Short Mesentery [PPT] Figure 3. Sonic Hedgehog [PPT] Figure 5. Toldt Fascia MESENTERY Double layer of peritoneum that encloses an organ and Ventral Mesentery suspends it from the posterior abdominal wall Intraperitoneal Derivative of the mesenchyme of the septum transversum ○ Organs enclosed by the peritoneum As the growth of the liver takes place, the ventral mesentery Retroperitoneal divides into the ff.: ○ Ventral Mesogastrium (Lesser Omentum) ○ 📖Organs posterior to peritoneum lining the body wall From the stomach and proximal-most part of the 📖 ○ Covered by peritoneum on the anterior surface only duodenum to the liver ○ Suspensory Ligament of Treitz: Goes up to the right ○ Falciform Ligament - anteriorly ○ ❗crus of the diaphragm (+) Secondarily Retroperitoneal 📖 From the liver to the ventral body wall Contains the umbilical vein at the free margin Initially intraperitoneal, but later becomes retroperitoneal Contains the pancreas and colon (both ascending 💡 GOOD TO KNOW: and descending) 📖Hepatoduodenal Ligament - posteriorly 💡 GOOD TO KNOW: contains the hepatic portal triad at the free margin We no longer use the terms intraperitoneal and retroperitoneal in Continuous with the dorsal mesentery the latest edition of Langman for Embryology, but for the sake of (+) Surgical importance learning anatomy, we will use it to describe the location of organs, Spread of infections especially for gross anatomy. Foregut, midgut, and hindgut are initially in contact with the mesenchyme of the posterior abdominal 5th Week: Narrowed Bridge ○ Dorsal Mesentery - Suspends the caudal, foregut, midgut, and major part of the hindgut from the abdominal wall ○ Pathway for blood vessels, lymphatics, and nerves Dorsal Mesogastrium Greater Omentum Mesoduodenum Mesentery Proper Mesocolon Mesoappendix Mesosigmoid Mesorectum Mesentery Figure 6. Primitive Dorsal and Ventral Mesenteries [PPT] ○ Collection of connective tissues that maintain the gut 📖Dorsal Mesentery tube and derivatives in their anatomical position Abdomen 📖 Extends from the lower end of the esophagus to the cloacal ○ Lower Esophagus to the rectum as a continuous sheet attached to the posterior body wall 📖○ In theDorsal region of the hindgut stomach region, it forms: 📖○ In theDorsal Mesogastrium/Greater Omentum Duodenal Region, it forms: 📖○ In theMesentery Mesoduodenum jejunal and Ileal Region, it forms: 📖○ In theDorsal Proper region of the Colon, it forms: Mesocolon Gives rise to 3 main arterial trunks: ○ Celiac Trunk ○ Superior Mesenteric Artery ○ Inferior Mesenteric Artery [PPT] Figure 4. Mesentery : LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 2 of 10  📖Table 3. Regions of the Dorsal Mesentery and its Derivatives REGION DERIVATIVES Stomach Dorsal Mesogastrium or Greater Omentum Duodenal Dorsal Mesoduodenum Jejunal & Ileal Mesentery Proper Colon Dorsal Mesocolon Peritoneum Continuous serous membrane lining the inner surface of the abdominal cavity from which it is reflected onto the viscera Visceral ○ in apposition to the viscera [PPT] Figure 9. Esophagus Parietal ○ attached to the abdominal wall Peritoneal Reflections Esophageal Abnormalities ○ where the peritoneum bridges the space between an Esophageal Atresia and/or Tracheoesophageal Fistula organ and the inner surface of the posterior abdominal ○ Spontaneous posterior deviation of the wall tracheoesophageal septum ○ Mechanical abnormality ○ Most common The proximal part ends as a blind sac; the distal part connected to the trachea above the bifurcation ○ Prevents normal passage of amniotic fluid – polyhydramnios Esophageal stenosis – narrow lumen ○ Incomplete recanalization, vascular abnormalities, accidents that compromise blood flow Congenital Hiatal Hernia ○ Failure of the esophagus to lengthen sufficiently ○ Stomach into the esophageal hiatus through the diaphragm Figure 7. Example of a Peritoneal Reflection: Falciform Ligament as it attaches to the ventral body wall [PPT] FOREGUT ESOPHAGUS 4 weeks old: Respiratory diverticulum Lung bud – ventral wall at the border with the pharyngeal gut Partitioned by tracheoesophageal septum Initially short but lengthens rapidly Ventral ○ Respiratory primordium Dorsal ○ Esophagus Muscular Coat: visceral mesenchyme ○ Upper two-thirds Striated Vagus [PPT] Figure 10. Esophageal Atresia ○ Lower third Smooth STOMACH Splanchnic plexus 4th week: Fusiform dilation close to the respiratory diverticulum Growth and lengthening of the esophagus are necessary for proper positioning. Appearance and position change greatly due to growth and changes in position ○ Rotates around a longitudinal and an AP axis 90 degrees clockwise- left side faces anteriorly, right side faces posteriorly Left vagus nerve innervates the anterior wall Right vagus nerve innervates the posterior wall GREATER AND LESSER CURVATURES ○ Posterior wall grows faster than the anterior position. [PPT] Figure 8. Esophagus : LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 3 of 10  [PPT Figure 14. Dorsal Mesogastrium 5th Week: spleen primordium appears ○ Mesodermal proliferation between the two leaves of the dorsal mesogastrium [PPT] Figure 11. Stomach Cephalic and caudal ends originally lie in the midline ○ PYLORIC: right and upward ○ CARDIAC: left and slightly downward ○ Final position- axis from above left to below right Rotation and disproportionate growth after the position of the mesenteries ○ Dorsal and Ventral mesogastrium [PPT Figure 14. Transverse section of the Dorsal Mesogastrium Dorsal mesogastrium lengthens ○ Portion between the spleen and dorsal midline swings to the left and becomes attached to the peritoneum by Toldt fascia [PPT] ○ Lienorenal Reflection Figure 12. Dorsal and Ventral mesogastrium Spleen to the posterior body wall ○ Gastrolineal Reflection: Spleen to the stomach ○ Lengthening and fusion of the dorsal mesogastrium determine the final position of the pancreas Initially grows into dorsal mesoduodenum The tail eventually extends into the dorsal mesogastrium Fuses with the dorsal body wall ○ AP axis: dorsal mesogastrium bulges down [PPT] Figure 13. Dorsal Mesogastrium GROWTH OF THE LIVER ○ Thinning of the mesoderm forming the ventral mesogastrium ○ Two parts of the ventral mesentery: Lesser omentum- stomach to the liver Falciform ligament- liver to the ventral body wall Rotation and disproportionate growth after the position of the [PPT’ Figure 14. Dorsal Mesogastrium mesenteries ○ Omental Bursa (lesser peritoneal sac) GREATER OMENTUM Longitudinal axis rotation pulls dorsal mesogastrium ○ Double-layered sac over the transverse colon and small to the left intestinal loops like an apron Space behind the stomach ○ Layer fuse to form a single sheet hanging from the ○ Pulls the lesser omentum to the right greater curvature. : LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 4 of 10  ○ Posterior layer fuses with the mesentery of the ○ Hypertrophy of the circular and longitudinal musculature transverse colon in the pylorus ○ Postnatal exposure increases risk (erythromycin) ○ Extreme narrowing of the pyloric lumen Obstructs passage of food Projectile vomiting Atretic pylorus DUODENUM Terminal part of the foregut and the cephalic part of the midgut ○ Junction is distal to the origin of the liver bud C shaped loop and rotates to the right ○ Rotation plus rapid growth of pancreatic head Swings duodenum from initial midline position to the right side [PPT Attach to posterior body wall Figure 15. Greater Omentum ○ Small portion of distal region- duodenal cap VENTRAL MESENTERY: lesser omentum and falciform Unattached to posterior body wall ligament ○ Form ventral mesogastrium ○ From mesoderm of the septum transversum LIVER CORDS INTO SEPTUM ○ Peritoneum of the liver ○ Falciform ligament from the liver to the ventral body wall ○ Lesser omentum from the stomach and upper duodenum to the liver [PPT] Figure 18. Duodenum 2th MONTH: Lumen is obliterated by cell proliferation ○ Recanalized shortly thereafter Figure 16. Embryo approx 32 days [PPT ROUND LIGAMENT OF THE LIVER (ligamentum teres hepatis) ○ Obliterated umbilical vein located in the free margin of the falciform ligament FREE MARGIN OF THE LESSER OMENTUM ○ Thickens to form the PORTAL PEDICLE Contains portal triad: bile duct, portal vein, hepatic artery ○ Roof of the EPIPLOIC FORAMEN (OF WINSLOW) Figure 19. Recanalization [PPT] Opening connecting the omental bursa (lesser sac) with peritoneal cavity (greater sac) BLOOD SUPPLY ○ Celiac Artery- foregut ○ Superior Mesenteric Artery- midgut [PPT Figure 17.Lesser Omentum Stomach Abnormalities [PPT] Pyloric Stenosis Figure 20 Blood Supplies in the Duodenum : LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 5 of 10  LIVER AND GALLBLADDER Appears in the middle of the 3rd week Outgrowth of the endodermal epithelium at the distal end of the foregut ○ Hepatic diverticulum (Liver Bud) Rapidly proliferating cells that penetrate the septum transversum. Mesodermal plate between the pericardial cavity and the stalk of the yolk sac While hepatic cells continue to penetrate the septum, the connection between the hepatic diverticulum and the foregut (duodenum) narrows. ○ Leads to the formation of the bile duct. Figure 22. 9-mm embryo (36 days) Small ventral outgrowth is formed and gives rise to the gallbladder and cystic duct. 10th Week of Development During further development, epithelial liver cords intermingle with the vitelline and umbilical veins and form the hepatic Weight of the liver is approximately 10% of the TBW. sinusoids. ○ Large number of sinusoids and hematopoietic ○ Liver cords differentiate into the parenchyma (liver cells) functions. and form the lining of the biliary ducts. Large nests of proliferating cells between hepatic cells and Hematopoietic cells, Kupffer cells, and connective tissue walls of the vessels. cells are derived mesoderm of the septum transversum. ○ Produce red and white blood cells. Gradually subsides during the last 2 months of intrauterine life - weight of the liver is then only 5% of TBW. 12th Week of Development Bile is formed by hepatic cells. Gallbladder and cystic duct have developed. ○ Cystic duct joined the hepatic duct to form the bile duct. Bile can enter the gastrointestinal tract. ○ Its contents take on a dark green color. Because of positional changes of the duodenum, entrance of the bile duct gradually shifts. ○ From its initial anterior position to a posterior one ○ Bile duct passes behind the duodenum Molecular Regulation of Liver Induction Figure 21. Primitive gastrointestinal tract and formation of liver bud (A). Epithelial liver cords penetrate the mesenchyme of septum tranversum (B). Fibroblast Growth Factors (FGF2) ○ Blocks inhibitors Invasion of Septum Transversum by Liver Cells ○ Secreted by cardiac mesoderm and by blood vessel-forming endothelial cells at the site of liver bud Mesoderm of the septum transversum between the liver and outgrowth the foregut and the liver and the ventral abdominal wall Bone Morphogenetic Proteins (BMPs) becomes membranous. ○ Secreted by septum transversum ○ Mesoderm between the liver and the foregut becomes ○ Enhance competence of liver endoderm to respond to the lesser omentum. FGF2 ○ Mesoderm between the liver and the ventral abdominal Differentiate into hepatocytes and biliary cell wall becomes the falciform ligament. lineages Hepatocyte nuclear transcription factors (HNF3 and Mesoderm on the Liver Surface 4) Differentiates into visceral peritoneum except on its cranial surface. Liver remains in contact with the rest of the original septum transversum. ○ Will form the central tendon of the diaphragm. ○ Bare area - in contact with future diaphragm, never covered by the peritoneum. Figure 23. Molecular regulation : LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 6 of 10 Liver and Gallbladder Abnormalities Accessory Hepatic Ducts and Duplication of Gallbladder ○ Asymptomatic Extrahepatic Biliary Atresia ○ Failure of ducts to recanalize ○ 15% to 20% correctable – remainder fatal unless liver transplant is done Intrahepatic Biliary Duct Atresia and Hypoplasia ○ Rare; fetal infections ○ Duct formation within liver itself ○ May be lethal but usually benign Figure 24. Pancreas during the 6th week of development (A). Fusion of pancreatic ducts (B). Molecular Regulation of Pancreas Development FGF2 and ACTIVIN ○ Produced by the notochord and endothelium of the dorsal aorta ○ Repress at SHH expression in endoderm destined to form the dorsal bud ○ Ventral bud induced by visceral mesoderm ○ Upregulates pancreatic and duodenal homeobox 1 (PDX) gene PAX4 and 6 – endocrine cell lineage Figure 23. Obliteration of the bile duct (A). Duplication of the gallbladder (B). Both: insulin, somatostatin, pancreatic polypeptide cells PANCREAS PAX6 only: glucagon cells Formed by two buds from the endodermal lining of the duodenum Pancreatic Abnormalities ○ Dorsal mesentery - dorsal pancreatic bud Annular Pancreas ○ Bile duct - ventral pancreatic bud ○ Left portion of ventral bud migrates in the opposite Duodenum rotates to the right and becomes C-shaped direction ○ Ventral bud moves dorsally ○ Duodenum surrounded by pancreatic tissue ○ Lie immediately below and behind the dorsal bud Accessory Pancreatic Tissue Parenchyma and duct systems of the dorsal and ventral ○ Distal end of the esophagus to the tip of the primary pancreatic buds fuse intestinal loop ○ Ventral bud gives rise to: ○ Most frequently: gastric mucosa and Meckel’s Uncinate process diverticulum Inferior head of the pancreas ○ Dorsal bud gives rise to the remaining parts. The main pancreatic duct (of Wirsung) is formed by: ○ Distal part of the dorsal pancreatic duct ○ Entire ventral pancreatic duct Proximal part of the dorsal pancreatic duct: ○ Either obliterated ○ Persists as a small channel, the accessory pancreatic duct (of Santorini) Major papilla ○ Entrance of the main pancreatic duct and the bile duct Minor papilla ○ Entrance of the accessory duct (if present) During the 3rd month of fetal life, pancreatic islets (of Langerhans) are formed. ○ From parenchymatous pancreatic tissue Figure 25. Annular pancreas. ○ Scatter throughout the pancreas ○ 5th month: insulin secretion begins MIDGUT ○ Glucagon- and somatostatin-secreting cells develop from 5TH WEEK parenchymal cells ○ Suspended from the dorsal abdominal wall by a short Visceral mesoderm forms the pancreatic connective tissue mesentery Vitelline Duct or Yolk Stalk ○ communication between midgut and yolk sac ADULT ○ Immediately distal to the entrance of the bile duct into the duodenum ○ Termination: junction of the proximal two-thirds of the transverse colon with the distal third BLOOD SUPPLY: Superior mesenteric artery Figure 23. Stages in the development of the pancreas. : LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 7 of 10  [PPT] Figure 26. Midgut Figure 28. Umbilical Herniation [PPT] Primary Intestinal Loop Rotation of the Midgut Rapid elongation of the gut and its mesentery Loop rotates around an axis formed by the SMA Apex: 270 degrees when complete ○ Open connection with the yolk sac by VITELLINE Elongation of the small intestinal loop continues DUCT Jejunum and ileum form a number of coiled loops Cephalic limb Large intestine lengthens but does not coil ○ Develops into distal duodenum, jejunum, part of the Occurs during herniation and during the return of the loops ileum into the abdominal cavity Caudal limb: ○ Lower portion of the ileum, cecum, appendix, ascending colon, proximal two-thirds of the transverse colon [PPT] Figure 28. Intestinal Loop Retraction of Herniated Loops 10th Week Regression of the mesonephric kidney Reduced hepatic growth Figure 27. Primary Intestinal Loop [PPT] Expansion of abdominal cavity Proximal part of the JEJUNUM ○ First part to reenter abdominal cavity – on the left side Physiological Umbilical Herniation ○ Later loops settle more to the right 6TH WEEK: CECAL BUD Rapid elongation of the cephalic limb ○ Conical dilation of the caudal limb Abdominal cavity too small to contain all loops ○ Last part to reenter the abdominal cavity 6TH WEEK: loops enter the extraembryonic cavity in the ○ Lies in the right upper quadrant directly below the liver umbilical cord ○ Descends into the right iliac fossa ○ Ascending colon and hepatic flexure on the right side APPENDIX ○ Narrow diverticulum at the distal end of the cecal bud ○ Develops during the descent of the colon ○ Final positions: Retrocecal Retrocolic : LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 8 of 10 Figure 29. Stages of Development : A - 7 WEEKS, B - 8 WEEKS, C- NEWBORN ○ Protrusion of abdominal contents directly into the [PPT] amniotic cavity ○ Right of the umbilicus ○ Defect: abnormal closure of the body wall around the connecting stalk ○ Not covered by peritoneum or amnion ○ Not associated with chromosome abnormalities or severe defects Vitelline Ducts Abnormalities Meckel’s / Ileal Diverticulum ○ Small portion of the vitelline duct persists ○ Outpocketing of the ileum ○ Usually asymptomatic in adults ○ Pancreatic tissue or gastric mucosa: ulceration, bleeding, perforation Gut Rotation Defects Volvulus ○ Twisting of the intestine [PPT] ○ Compromised blood supply Figure 29. Appendix ○ 90-degree rotation only ○ Colon and cecum – first to return and settle on the left Mesenteries of the Intestinal Loops side MESENTERY PROPER ○ Others move more to the right ○ Profound changes with rotation and coiling of the bowel ○ Caudal limb of the loop moves to the right side: dorsal HINDGUT mesentery twists around the origin of the SMA Gives rise to: ○ Midgut and hindgut remains continuous as a single ○ Distal third of the transverse colon, entity ○ Descending colon, ○ FREE MESENTERY ○ Sigmoid, appendix, lower end of cecum, sigmoid colon ○ Rectum, ○ Ascending and descending portions of the colon ○ And the upper part of the anal canal ○ Mesenteries attach to the peritoneum of the posterior Endoderm: internal lining of the bladder and urethra body cavity by Toldt fascia Figure 30. Intestinal Loop [PPT] Figure 31. Hindgut overview MIDGUT ABNORMALITIES Table 4. Hindgut divisions Abnormalities of the Mesenteries Division Parts / Description Volvulus Cloaca Posterior region – entrance of the ○ Mobile colon due to failure of the ascending colon to fuse Primitive anorectal region terminal portion of the hindgut with the posterior body wall Retrocolic Hernia Cloaca ○ Incomplete fusion gives rise to retrocolic pockets behind the ascending mesocolon o Entrapment of portions of Anterior region – entrance of Primitive urogenital sinus the small intestine behind the mesocolon the allantois Body Wall Defects Omphalocele Parts of Hindgut Formation ○ Herniation of abdominal viscera through an enlarged ○ Cloaca - endoderm-lined cavity covered by surface umbilical ring ectoderm at its ventral boundary ○ Covered by amnion ○ Cloacal membrane - Boundary between the endoderm ○ Failure to return to the body cavity from physiological and ectoderm herniation ○ Urorectal septum - Separates the region between the ○ High mortality rate and severe malformations : Gastroschisis ❗ allantois and hindgut Wedge of mesoderm LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 9 of 10  ❗Tip: comes to lie close to the cloacal membrane ❗Aganglionic megacolon or Hirschsprung disease Rectum in most cases END OF 7TH WEEK Extends to the midpoint of the sigmoid Cloacal membrane ruptures in 80% of cases Formation of perineal body Divisions UPPER PART (two-thirds) of the anal canal REFERENCES ○ Endoderm of the hindgut 1. Sadler, T.W.. (2019). Langman's medical embryology, 14th LOWER PART (one-third) ed.. Philadelphia: Wolters Kluwer. ○ Ectoderm around the proctodeum 2. Powerpoint (2024) Dr. Del Rosario - DA of Digestive System Table 5. Hindgut parts REVIEW QUESTIONS ❗ Parts Description 1. Fusiform dilation close to the respiratory diverticulum at what Proliferation and invagination of the week? ectoderm A. 12th week Anal pit Proctodeum on the surface of part of B. 4th week the cloaca C. 5th week D. 9th week Degeneration establishes continuity Anal membrane between the upper and lower parts of 2. This enhances the competence of liver endoderm to respond to (cloacal membrane) the anal canal FGF2? A. Fibroblast Growth Factors CAUDAL: inferior rectal arteries B. Bone Morphogenetic Proteins (BMPs) C. Vitelline Duct or Yolk Stalk ○ Branches of internal pudendal D. Lesser Omentum arteries Anal canal CRANIAL: superior rectal artery 3. What happens during the second month in duodenum? ○ Continuation of the inferior A. Lumen is obliterated by cell proliferation mesenteric artery B. It is partitioned by tracheoesophageal septum C. Rotates around a longitudinal and an AP axis Delineates junction between the D. Leads in the formation of the bile duct endodermal and ectodermal regions 4. Entrance of main pancreatic duct and the bile duct of the anal canal A. Major papilla Location: Below the anal columns ❗ Pectinate line B. Minor papilla Columnar to stratified squamous C. Both A and B epithelium D. Anterior pancreatic tissue 5. These are organs that are posterior to the peritoneum lining the body wall? A. Intraperitoneal HINDGUT ABNORMALITIES B. Narrowed bridge C. Retroperitoneal Table 6. Hindgut parts D. Toldt Fascia Division Parts / Description Abnormalities in formation of the ❗ cloaca and/or the urorectal septum ANSWERS: 5C,4A,3A,2B,1B Opening of the hindgut shifts anteriorly – opening into the urethra Rectourethral and rectovaginal fistulas or vagina ❗ Cloaca is too small Septum does not extend far enough caudally May leave a narrow tube or fibrous remnant connected to the surface Rectoanall fistulas and atresias ❗ Misexpression of genes Anal membrane fails to breakdown Imperforate anus Congenital ❗Absence of parasympathetic ganglia megacolon in the bowel wall APPENDIX : LE 3 Trans 2 TG: Belmonte, Mendoza, Olvida, Sabayle | Lerio, Ong Lo Page 10 of 10