liver, and pancreas formation of the gut, entodermal ... · esophageal atresia or...
TRANSCRIPT
Entodermal derivatives:formation of the gut,liver, and pancreas
Mike Gershon
Folding formsthe gut
Primitive gut extends frombuccopharyngeal to cloacalmembrane.
Move toward each other
Cardiogenic mesenchyme isoriginally rostral, but foldingbrings it caudal to buccalmembrane.
Foregut and hindgut becomerecognizable
Portion of yolk sac isincoporated into the embro asbowel.
Midgut remains open.
Cephalocaudal and lateralfolding occur simultaneously
Meeting and fusion of cranial, lateral, and caudal edges of the embryocreate the primordial foregut and hindgut
Slow fusion of midgut-due to presence of yolk sac. Midgut remains open untilweek 6-connects to yolk sac via vitelline duct.
Buccopharyngeal membrane opens at 4 and cloacal membrane at 7 weeks
Flexion delimits the bowel
After the gut forms, it is attached to the body wall bydorsal and ventral mesenteries; ventral is lost except inregion of liver. Vetelline duct remains in umbilical cord.
Anterior-posterior and lateralfolding form the primitive gut
Embryonic disc growsfaster in length than theyolk sac causing theembryo to bend.
Dorsal surface grows morerapidly than the ventral
Lateral foldingFusion with apposing sideexcept in the region of theyolk sac, and allantois
Folding brings the heartand septum transversumcaudal to bucco-pharyngeal membrane.
The dorsalmesentery
thins toallow the gutto be flexiblysuspended
The foregut has manyderivatives
Pharynx and its derivatives
Lower Respiratory tract
Esophagus
Stomach
Duodenum proximal to ampulla of Vater
Liver
Biliary Apparatus
Pancreas
From stomach to biliary apparatus, all are suppliedby the celiac artery, “the artery of the foregut.”
Esophaguselongates rapidly
Appears to grow faster at its cranialthan caudal end.
Stomach does not descend butarises from a region just caudal toseptum transversum that has beenfated to be stomach.
Epithelium obliterates lumen ofesophagus and is recanalized byapoptosis (week 8).
Failure causes polyhydramnios
Esophageal atresia or tracheo-esophageal fistula.
Stomach enlarges and rotates
Obliteration of the lumen andrecanalization occurs
The stomach rotates 90° in aclockwise direction
Dorsal surface grows faster than the ventral to create thegreater and lesser curvature. Acquires a transverse position
Rotation ofthe stomachcreates thelesser sacDorsal mesogastriummoves to left.
Ventral mesogastriumattaches to liver andbody wall.
Inferior recess formthe greater omentum
Layers fuse toobliterate the lessersac
Rotation of the stomachforms the omental bursa
Movements of the mesenteryand stomach are made
possible by vacuolization dueto selective apoptosis
Liver, biliary system andpancreas arise from the
duodenum
Hepatic diverticulum growsfrom the duodenum into the
ventral mesenteryBegins ~ week 4
Divides into cranialand caudal buds.
Cranial bud growsfaster and becomesthe hepaticparenchyma;
Hematopoieticcolonists arrive ~week 6
Caudal bud givesrise to the biliarysystem.
Ventral mesentery forms falciformligament, hepatic peritoneum, and
lesser omentum
Ventral mesogastriumsupports liver and stomach
Rotation of the stomachshapes the pancreas
Pancreas arises from dorsal and ventralbuds.
Rotation brings ventral to dorsal bud.
Buds fuse.Ventral duct becomes the main pancreatic ductbut the dorsal bud forms most of the pancreas
Ventral bud forms only the uncinate processand inferior part of the head of the pancreas.
Aberrant rotation causes anannular pancreas
Review of the Gut Tube
Derivatives of the midgut
Small intestine (except for the proximalduodenum.
Cecum
Appendix
Ascending colon
Right 1/2 to 2/3 of the proximal transversecolon
All are supplied by the superior mesentericartery (“the artery of the midgut”)
The midgutgrows
rapidly andherniatesinto the
umbilicalcord
Week 6
The midgutrotates
around anaxis of thesuperior
mesentericartery:
1. 90°2. 180°
Midgut hernia reduced atweek 10.
Rotation of the midgut
1. Cranial and caudal loop form.
2. Cranial growth >>> caudal growth.
3. Apex of loop is vitelline duct.
4. Cranial loop moves to right and caudal loop toleft (90° counterclockwise).
4. Reduction of midgut hernia with rotation afurther 180°.
Brings cecum to right
Moves down
Becomes secondarily retroperitoneal.
Loops of bowel fuse with thebody wall and become
secondarily retroperitoneal
Volvulus is a seriouscomplication of excessive
flexibility
Derivatives of the hindgut
Left 1/3 to 1/2 of the distal transverse colon
Descending colon
Sigmoid colon
Rectum
Superior part of anal canal
Epithelium of unrinary bladder and most of theurethra
All are supplied by the inferior mesentericartery, “the artery of the”. hindgut
The hindgut is originally acloaca-partioned to form
rectum and urogenital sinus
Urorectal septum divides thecloaca
Hindgutforms
superior 2/3of rectalcanal;
proctodeumforms lower1/3; dividedat pectinate
line
Never forgetthe pectinate
line
If anything can go wrong itwill; anorectal malformations
The END
Have a nice day!