Week 4: Pelvic & Perineum General Development of Urogenital System

Week 4 EmbryologyDevelopment of Gastrointestinal Dr Marselina TanLearning objectivesTopic : development of gastrointestinal and pelvic organ

Students should be able to:know the embryonic development of digestive organdescribe the congenital abnormality and the aging of digestive organ Derivatives of the endodermal germ layer: the gastrointestinal tractThe gastrointestinal tract formation depends on cephalocaudal & lateral folding of the embryoAs a result from folding movements initial wide communication between embryo & yolk sac narrow the vitelline duct remains

In the anterior, endoderm forms : foregutIn the tail region, endoderm forms: hindgut. Between: midgutThe endoderm forms the lining of the GIT, and cells of glands.The splanchnic mesoderm forms stroma (connective tissue) of the gland, muscle, and connective tissue of the gut wall. Midgut yolk sac by broad stalk: vitelline duct the vitellin ductAt cephalic end, foregut bounded temporarily by ectodermal-endodermal membrane: buccopharyngeal membrane 4th week ruptures: open connection amniotic cav. & primitive gut. Hindgut 7th week breaks down : create openings: cloacal membraneImportant result of cephalocaudal & lateral folding: partial incorporation of allantois into the body of embryo forms cloacaIn human, yolk sac vestigial : has nutritive role in early stages

Gastrointestinal tube is derivatives from primitive gut. When endoderm folds foregut (anterior) and hindgut (posterior). In the middle midgut

5At day 28th , gastrointestinal tube buds form digestive glands: - liverpancreasbile

Gastrointestinal tube differentiates further

6Gastrointestinal tube and its derivatives

Posterior: pharynx, gastrointestinal tube, oesofagus, gut, small intestine & large intestine.

Endoderm cells become epithelial lining digestive tube and glands.

Mesenchyme mesodermal cells will surround the tube and become peristaltic muscles. 7Mesenteries Initially, the gut is in contact with the posterior body wall.By 5th week, the connecting tissue (mesenchyme) between the gut and body wall narrows.Thus, caudal part of the foregut, midgut and major part of the hindgut are suspended by the dorsal mesentery.Dorsal mesentery forms- greater omentum, mesoduodenum, mesocolon and mesentery.

Figure is from Langmans EmbryologyMesenteries Ventral mesentery exists only at the lower end of esophagus, stomach and upper part of the duodenum.Ventral mesentery is derived from the septum transversum.The growth of the liver into the septum transversum results in division of the ventral mesentery.The part of the ventral mesentery between the liver and stomach forms the lesser omentum.The part between the liver and anterior abdominal wall forms the falciform ligament.

Figure is from Langmans EmbryologyForegut The part of the foregut extending from the buccopharyngeal membrane to the respiratory diverticulum is called pharyngeal gut (considered with pharyngeal arches).Remaining part extends from the respiratory diverticulum to the liver bud.Esophagus:- develops from the foregut between the respiratory diverticulum and stomach.-The muscle wall develops from the splanchnic mesoderm (upper 1/3-skeletal, middle 1/3-mixed and lower 1/3-smooth).-It elongates due to the descent of heart and lungs.

Figure is from Langmans EmbryologyEsophageal abnormalities Esophageal atresia/ tracheo-esophageal fistula:- due to abnormal tracheo-esophageal septum formation or some mechanical factors.-In common form, the proximal part of the esophagus ends blindly, and the distal part is connected to the trachea.Atresia of the esophagus prevents the passage of amniotic fluid into the gut thus accumulating the fluid in the amniotic sac-polyhydramnios.Esophageal stenosis:- narrow lumen.

Figure is from Langmans EmbryologyStomach Appears as a fusiform dilation of the foregut (4 week).Later, the appearance and position change due to differential growth and change in surrounding organs.It rotates 90 degrees clockwise around a longitudinal axis.-So that left side becomes the anterior surface and the right side becomes the posterior surface.-The left margin grows faster than the right resulting in the formation of the greater and lesser curvatures.The pyloric end moves to the right and the cardiac end moves to the left.

Figure is from Langmans EmbryologyStomach Stomach is attached to the dorsal body wall by dorsal mesogastrium and to the ventral by ventral mesogastrium.Rotation of the stomach results in creation of a space behind it called omental bursa (lesser sac).In the dorsal mesogastrium, spleen develops from the mesenchyme (5th week).-from dorsal mesogastrium-greater omentum, lienorenal and gastrosplenic ligaments develop.

Figure is from Langmans EmbryologyDuodenum Formed from the terminal part of the foregut and cranial part of the midgut.Origin of the liver bud marks the junction of 2 parts of the gut.Initially, the duodenum is a straight tube, but due to the rotation of stomach, duodenum assumes a C-shaped structure and lies to the right.The head of the pancreas grows into the concavity of the duodenum.Both of them become retroperitoneal.During 2nd month, the lumen becomes obliterated by cells, but later re-canalization takes place.In summary- First part and upper part of second part up to the bile duct develops from the foregut.-Remaining of the duodenum develops from the midgut.

Figure is from Langmans Embryology

A. Anterior view of the intestinal loops after 270 counterclockwise rotation. Note the coiling of the small intestinal loops and the position of the cecal bud in the right upper quadrant of the abdomen. B. Similar view as in A, with the intestinal loops in their final position. Displacement of the cecum and appendix caudally places them in the right lower quadrant of the abdomen.Liver and gall bladder The liver bud (endodermal) grows from the terminal part of the foregut during middle of the third week.This bud with proliferating cells grows into the septum transversum (mesodermal).The connection between the cellular proliferation and foregut narrows and becomes the bile duct.A cystic bud grows from the bile duct to form the gall bladder and cystic duct.The hepatocytes develop from endoderm.The blood cells, Kupffer cells and connective tissue and its cells develop from the mesoderm of the septum transversum.During 10 week, liver forms 10% of body weight, whereas at birth it is only 5%.

Figure is from Langmans EmbryologyLiver and gall bladder abnormalities Accessory hepatic ducts-common-without any problem.Duplication of gall bladder- common-without any problem.However, during surgery that is important to avoid any injury.Extrahepatic biliary atresia: 1/15,000 live births. -due to failure in re-canalization of duct during development.Intrahepatic biliary duct atresia: biliary duct inside liver is not canalized.

Figure is from Langmans EmbryologyDevelopment of pancreas Develops from 2 dorsal and ventral endodermal buds from duodenum.The ventral bud rotates to the left and lies below the dorsal bud.Both buds fuse and form the pancreas.Ventral bud forms the uncinate process and inferior part of the head.The dorsal bud forms the rest of the pancreas.

Figure is from Langmans EmbryologyPancreasThe main pancreatic duct is formed by the union of distal part of the duct of the dorsal bud with the duct of the ventral bud.The accessory pancreatic duct is formed from the proximal part of the duct of the dorsal bud.Third month-islets of Langerhans develop from pancreatic tissue-endodermal.The connective tissue of the gland-develops from the splanchnic mesoderm.5th month, insulin secretion begins.

Figure is from Langmans EmbryologyPancreatic abnormalities 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.-Obstructs the duodenum.Accessory pancreatic tissue:-Lies frequently in the mucosa of the stomach and Meckels diverticulum.Figure is from Langmans Embryology

Congenital malformations of the digestive tract atresia or stenosis of digestive tract: caused by failure of recanalization or improper recanalization, mostly in esophagus and duodenum

stenosisA, the most common, occurs in 50% of cases; B and C occur in 20% each of cases, and D occurs in 5% of cases. Most are caused by vascular accidents; those in the upper duodenum may be caused by a lack of recanalization. Atresias (A-C) occur in 95% of cases, and stenoses (D) in only 5%. congenital umbilical hernia: caused by incomplete closure of the central part of the abdominal wall, the viscera return to the abdomen but herniated again during the fetal period

A. Omphalocele showing failure of the intestinal loops to return to the body cavity after physiological herniation. The herniated loops are covered by amnion. B. Omphalocele in a newborn. C. Newborn with gastroschisis. Loops of bowel extend through a closure defect in the ventral body wall and are not covered by amnionOmphaloceleOccurs in 1 in 6,000 birthsGI structures protrude through an unclosed umbilical ring, covered in membranesHerniated organs may not have fully retracted in the 10th wk (likely if amnion covered only)Or, if there is peritoneum in the sac, the organs retracted but herniated again secondarily when the ventral abdominal wall failed to closeOmphalocele to 1/3 have other anomalies or chromosomal defectsPentology of Cantrell (failure of migration and fusion of the lateral and cephalic folds): omphalocele, diaphragmatic hernia, sternal cleft, ectopia cordis (evagination of the heart), & intracardiac anomalyBeckwith-Wiedeman Syndrome: omphalocele, macroglossia, macrosomia, hemihypertrophy, hypoglycemia related to pancreatic hyperplasiaAssociated with Trisomy 13, 18, &21

GastroschisisOccurs in 1 in 10,000 birthsDefect of the ventral abdominal wall between the rectus muscles lateral to the umbilicusOccurs on the right sideArises through an abnormality in the involution of the right umbilical vein during the 5th & 6th wks causing a maldevelopment of associated mesodermal elements in that region of the body wall

GastroschisisNot covered by a membraneHerniated intestine is often edematous, and can be ischemic- especially if the defect is smallIncreased risk of sepsisIncreased fluid and heat lossesNot associated with other abnormalities

congenital aganglionic megacolon: results from the absence of ganglion cell of the parasympathetic ganglia, which cause failure of the distal segment to move the intestinal contents onward HIRSCHPRUNG

imperforate anus, rectal atresia and rectal fistula: ---imperforate anus: results from failure rupture of anal membrane

imperforate anusUrorectal (A) and rectovaginal (B) fistulas that result from incomplete separation of the hindgut from the urogenital sinus by the urorectal septum. These defects may also arise if the cloaca is too small, which causes the opening of the hindgut to shift anteriorly. C. Rectoperineal (rectoanal atresia). These defects probably result from vascular accidents involving the caudal region of the hindgut, resulting in atresias and fistulas. D. Imperforate anus resulting from failure of the anal membrane to break down. abnormal rotation of the intestinal loop: nonrotation or reversed rotation of the midgut

atresia of the gall bladder and bile ducts: results from failure of vacuolization of the epithelial cords or reopen

A. Abnormal rotation of the primary intestinal loop. The colon is on the left side of the abdomen, and the small intestinal loops are on the right. The ileum enters the cecum from the right. B. The primary intestinal loop is rotated 90 clockwise (reversed rotation). The transverse colon passes behind the duodenum.