EntodermalEntodermal derivatives:derivatives: formationformation ofof thethe gut,gut, liver,liver, andand pancreaspancreas
MikeMike GershonGershon FoldingFolding formsforms thethe gutgut
¾ Primitive gut extends from buccopharyngeal to cloacal membrane.
z Move toward eacheach otherother ¾ Cardiogenic mesenchyme is originally rostral, but folding brings it caudal to buccal membrane. ¾ Foregut and hindgut become recognizable ¾ Portion of yolk sac is incoporated into the embro as bowel. ¾ Midgut remains open. CephalocaudalCephalocaudal andand laterallateral foldingfolding occuroccur simultaneouslysimultaneously
¾ Meeting and fusionfusion ofof cranial,cranial, lateral,lateral, andand caudalcaudal edgesedges ofof thethe embryoembryo create the primordialprimordial foregutforegut andand hindguthindgut
z Slow fusion of midgut-due to presence of yolk sac. Midgut remains open until week 6-connects to yolk sac via vitelline duct.
z Buccopharyngeal membrane opens at 4 and cloacal membrane at 7 weeks FlexionFlexion delimitsdelimits thethe bowelbowel
¾ After the gut forms, it is attached to the body wall by dorsal and ventral mesenteries; ventral is lost except in region of liver. Vetelline duct remains in umbilical cord.
Anterior-posteriorAnterior-posterior andand laterallateral foldingfolding formform thethe primitiveprimitive gutgut ¾ Embryonic disc grows faster in length than the yolk sac causing the embryo to bend.
z Dorsal surface grows more rapidly thanthan thethe ventralventral ¾ Lateral folding
z Fusion withwith apposingapposing sideside except in the region ofof thethe yolk sac, andand allantois ¾ Folding brings the heart and septum transversum caudal to bucco- pharyngeal membrane. TheThe dorsaldorsal mesenterymesentery thinsthins toto allowallow thethe gutgut toto bebe flexiblyflexibly suspendedsuspended TheThe foregutforegut hashas manymany derivativesderivatives ¾ Pharynx and its derivatives ¾ Lower Respiratory tract ¾ Esophagus ¾ Stomach ¾ Duodenum proximal to ampulla of Vater ¾ Liver ¾ Biliary Apparatus ¾ Pancreas FromFrom stomachstomach toto biliarybiliary apparatus,apparatus, allall areare suppliedsupplied byby thethe celiacceliac artery,artery, ““thethe arteryartery ofof thethe foregut.foregut.”” EsophagusEsophagus elongateselongates rapidlyrapidly
¾ Appears to grow faster at its cranial than caudal end. ¾ Stomach does not descend but arises from a region just caudal to septum transversum that has been fated to be stomach. ¾ Epithelium obliterates lumen of esophagus and is recanalized by apoptosis (week 8).
z Failure causes polyhydramnios
z Esophageal atresia or tracheo- esophageal fistula.fistula. ¾ Stomach enlarges and rotates ObliterationObliteration ofof thethe lumenlumen andand recanalizationrecanalization occursoccurs TheThe stomachstomach rotatesrotates 9090°° inin aa clockwiseclockwise directiondirection
¾ Dorsal surface grows faster than the ventral to create thethe greater and lesser curvature. Acquires a transverse position RotationRotation ofof thethe stomachstomach createscreates thethe lesserlesser sacsac
¾ Dorsal mesogastrium moves to left. ¾ Ventral mesogastrium attaches to liver and body wall. ¾ Inferior recess form the greater omentum
z Layers fuse to obliterate thethe lesserlesser sac RotationRotation ofof thethe stomachstomach formsforms thethe omentalomental bursabursa MovementsMovements ofof thethe mesenterymesentery andand stomachstomach areare mademade possiblepossible byby vacuolizationvacuolization duedue toto selectiveselective apoptosisapoptosis Liver,Liver, biliarybiliary systemsystem andand pancreaspancreas arisearise fromfrom thethe duodenumduodenum HepaticHepatic diverticulumdiverticulum growsgrows fromfrom thethe duodenumduodenum intointo thethe ventralventral mesenterymesentery
¾ Begins ~ week 4 ¾ Divides into cranial and caudal buds. ¾ Cranial bud grows faster and becomes the hepatic parenchyma;
z Hematopoietic colonists arrive ~~ week 6 ¾ Caudal bud gives rise to the biliary system. VentralVentral mesenterymesentery formsforms falciformfalciform ligament,ligament, hepatichepatic peritoneum,peritoneum, and lesserlesser omentumomentum VentralVentral mesogastriummesogastrium supportssupports liverliver andand stomachstomach RotationRotation ofof thethe stomachstomach shapesshapes thethe pancreaspancreas
¾ Pancreas arises from dorsal and ventral buds. ¾ Rotation brings ventral to dorsal bud. ¾ Buds fuse.
z Ventral duct becomes thethe mainmain pancreaticpancreatic ductduct but the dorsal bud forms most of the pancreas
z Ventral bud forms onlyonly thethe uncinate process and inferior part of the headhead ofof thethe pancreas.pancreas. AberrantAberrant rotationrotation causescauses anan annularannular pancreaspancreas ReviewReview ofof thethe GutGut TubeTube DerivativesDerivatives ofof thethe midgutmidgut
¾ SmallSmall intestineintestine (except for the proximal duodenum.duodenum. ¾ CecumCecum ¾ AppendixAppendix ¾ AscendingAscending colon ¾ RightRight 1/21/2 toto 2/32/3 of the proximal transverse coloncolon ¾ AllAll areare supplied by the superior mesenteric arteryartery ((““thethe arteryartery ofof the midgutmidgut””)) TheThe midgutmidgut growsgrows rapidlyrapidly andand herniatesherniates intointo thethe umbilicalumbilical cordcord Week 6 TheThe midgutmidgut rotatesrotates aroundaround anan axisaxis ofof thethe superiorsuperior mesentericmesenteric artery:artery: 1.1. 9090°° 2.2. 180180°° Midgut hernia reduced at week 10. RotationRotation ofof thethe midgutmidgut
¾ 1. Cranial and caudal loop form. ¾ 2. Cranial growth >>> caudal growth. ¾ 3. Apex of loop is vitelline duct. ¾ 4. Cranial loop moves to right and caudal loop to left (90° counterclockwise). ¾ 4. Reduction of midgut hernia with rotation a further 180°.
z Brings cecum to right
z Moves down
z Becomes secondarily retroperitoneal. LoopsLoops ofof bowelbowel fusefuse withwith thethe bodybody wallwall andand becomebecome secondarilysecondarily retroperitonealretroperitoneal
VolvulusVolvulus isis aa seriousserious complicationcomplication ofof excessiveexcessive flexibilityflexibility
DerivativesDerivatives ofof thethe hindguthindgut
¾ Left 1/3 to 1/2 of the distal transversetransverse coloncolon ¾ Descending colon ¾ Sigmoid colon ¾ Rectum ¾ Superior part of anal canal ¾ Epithelium of unrinary bladder and most of the urethra ¾ All are supplied by the inferior mesenteric artery, “the artery of the”. hindgut TheThe hindguthindgut isis originallyoriginally aa cloacacloaca--partionedpartioned toto formform rectumrectum andand urogenitalurogenital sinussinus UrorectalUrorectal septumseptum dividesdivides thethe cloacacloaca HindgutHindgut formsforms superiorsuperior 2/32/3 ofof rectalrectal canal;canal; proctodeumproctodeum formsforms lowerlower 1/3;1/3; divideddivided atat pectinatepectinate lineline NeverNever forgetforget thethe pectinatepectinate lineline IfIf anythinganything cancan gogo wrongwrong itit will;will; anorectalanorectal malformationsmalformations TheThe ENDEND
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