EMBRYOLOGY OF EMBRYOLOGY OF DIGESTIVE SYSTEMDIGESTIVE SYSTEM

AHMAD AMINUDDINAHMAD AMINUDDIN

DIVISION OG THE GUT TUBEDIVISION OG THE GUT TUBE

ENDODERM-LINED YOLK SAC CAVITY ENDODERM-LINED YOLK SAC CAVITY FORMS THE PRIMITIVE GUT.FORMS THE PRIMITIVE GUT.

- YOLK SAC.- YOLK SAC. - ALLANTOIS.- ALLANTOIS. PRIMITIVE GUT FORM PRIMITIVE GUT FORM - FORE GUT.- FORE GUT. - HIND GUT.- HIND GUT. - MID GUT - MID GUT - VITELLINE DUCT.- VITELLINE DUCT. - YOLK SAC - YOLK SAC

MESENTERIESMESENTERIES

Initially the fore gut , mid gut and hind gut are Initially the fore gut , mid gut and hind gut are in broad contact with the mesenchyme of the in broad contact with the mesenchyme of the posterior abdominal wall.posterior abdominal wall.

By the fifth week, the connecting tissue bridge By the fifth week, the connecting tissue bridge has narrowed, the caudal part of the fore gut , has narrowed, the caudal part of the fore gut , the mid gut and major part of the hind gut are the mid gut and major part of the hind gut are suspended from the abdominal wall by the suspended from the abdominal wall by the dorsal mesentery.dorsal mesentery.

DORSAL MESENTERYDORSAL MESENTERY

DORSAL MESOGASTRIUM OR DORSAL MESOGASTRIUM OR GREATER OMENTUM.GREATER OMENTUM.

DORSAL MESODUODENUM.DORSAL MESODUODENUM. DORSAL MESOCOLON.DORSAL MESOCOLON. MESENTERY PROPER.MESENTERY PROPER.

VENTRAL MESENTERYVENTRAL MESENTERY

From the terminal part of the esophagus, From the terminal part of the esophagus, stomach and the upper part of the duodenum is stomach and the upper part of the duodenum is derived from the SEPTUM TRANSVERSUM.derived from the SEPTUM TRANSVERSUM.

Growth of the liver divides the ventral Growth of the liver divides the ventral mesentery into ;mesentery into ;

- the lesser omentum.- the lesser omentum.

- the falciform ligament.- the falciform ligament.

FOREGUTFOREGUT ESOPHAGUSESOPHAGUS - When the embryo is approximately 4 weeks - When the embryo is approximately 4 weeks old the respiratory diveticulum ( lung bud ) old the respiratory diveticulum ( lung bud ) appear at the ventral wallof the foregut.appear at the ventral wallof the foregut. - The tracheobronchial septum gradually parti-- The tracheobronchial septum gradually parti- tions this diverticulum from the ventral part tions this diverticulum from the ventral part of the foregut ;of the foregut ; - the respiratory primordium ---- ventral.- the respiratory primordium ---- ventral. - the esophagus ---- dorsal.- the esophagus ---- dorsal.

STOMACHSTOMACH

DUODENUMDUODENUM

The terminal part of the foregut and the The terminal part of the foregut and the cephalic end of the midgut.cephalic end of the midgut.

As the stomach rotates, duodenum takes on the As the stomach rotates, duodenum takes on the form of a C-shaped loop and rotates to the form of a C-shaped loop and rotates to the right.right.

This rotation togather with rapid growth of the This rotation togather with rapid growth of the head of the pancreas , swing the duodenum to head of the pancreas , swing the duodenum to the left side of the abdominal cavity.the left side of the abdominal cavity.

DUODENUMDUODENUM

The duodenum and head of the pancreas press The duodenum and head of the pancreas press against the dorsal body wall, the right surface against the dorsal body wall, the right surface of the dorsal mesoduodenum fuses with the of the dorsal mesoduodenum fuses with the adiacent peritonium.adiacent peritonium.

A small proximal portion of the duodenum A small proximal portion of the duodenum retains its mesentery and remains retains its mesentery and remains intraperitoneal.intraperitoneal.

LIVER AND GALLBLADDERLIVER AND GALLBLADDER

The hepatic diverticulum or liver bud appears The hepatic diverticulum or liver bud appears in the middle of the third week as an outgroeth in the middle of the third week as an outgroeth of the endodermal epithelium at the distal end of the endodermal epithelium at the distal end of the foregut. This outgrowth penetrate the of the foregut. This outgrowth penetrate the septum transversum.septum transversum.

The connection between the hepatic The connection between the hepatic diverticulum and the foregut, narrows forming diverticulum and the foregut, narrows forming the bile duct.the bile duct.

LIVER AND GALL BLADDERLIVER AND GALL BLADDER

A small ventral outgrowth of the bile duct give A small ventral outgrowth of the bile duct give rise to the gallblader and the cystic duct.rise to the gallblader and the cystic duct.

Hematopoietic cells , Kupffer cells and Hematopoietic cells , Kupffer cells and connective tissue cells derived from mesoderm connective tissue cells derived from mesoderm of the septum transversum.of the septum transversum.

Mesoderm of the septum transversum between Mesoderm of the septum transversum between - the liver and foregut ----- lesser omentum.- the liver and foregut ----- lesser omentum. - the liver and ventral abdominal wall, -------- the liver and ventral abdominal wall, ------- ---- falciform ligament---- falciform ligament

LIVER AND GALLBLADDERLIVER AND GALLBLADDER

Peritoneal connection between the foregut and Peritoneal connection between the foregut and ventral abdominal wall --- ventral mesentery.ventral abdominal wall --- ventral mesentery.

The bare area of the liver , remain incontact The bare area of the liver , remain incontact with the rest of the original septum with the rest of the original septum transversum, this portion of septum will forms transversum, this portion of septum will forms the central tendon of the diaphragm.the central tendon of the diaphragm.

PANCREASPANCREAS

Endodermal lining of duodenum.Endodermal lining of duodenum.

- dorsal pancreatic bud.- dorsal pancreatic bud.

- ventral pancreatic bud.- ventral pancreatic bud. When the duodenum rotates tothe right – the When the duodenum rotates tothe right – the

ventral pancreatic bud comes to lie below and ventral pancreatic bud comes to lie below and behind the dorsal bud.behind the dorsal bud.

Later the parenchyma and the duct system of Later the parenchyma and the duct system of the dorsal and ventral pancreatic bud fuse.the dorsal and ventral pancreatic bud fuse.

PANCREASPANCREAS

The ventral bud forms the uncunate process The ventral bud forms the uncunate process and inferior part of the head.and inferior part of the head.

The remaining part of the gland is derived The remaining part of the gland is derived from the dorsal bud.from the dorsal bud.

The main pancreatic duct ( of Wirsung ) is The main pancreatic duct ( of Wirsung ) is formed by the distal part of the dorsal formed by the distal part of the dorsal pancreatic duct and the entire ventral pancreatic duct and the entire ventral pancreatic duct.pancreatic duct.

PANCREASPANCREAS

The proximal part of the dorsal pancreatic duct The proximal part of the dorsal pancreatic duct eithe is obliterated or persist as a small channel eithe is obliterated or persist as a small channel , the accessory pancreatic duct ( of Santorini ), the accessory pancreatic duct ( of Santorini )

The main pancreatic duct , together with the The main pancreatic duct , together with the bile duct, enter the duodenum at the major bile duct, enter the duodenum at the major papilla.papilla.

The entrance of the accessory duct ( when The entrance of the accessory duct ( when present ) is at the minor papilla.present ) is at the minor papilla.

PANCREASPANCREAS In the third month, pancreatic islets ( of In the third month, pancreatic islets ( of

Lngerhans ) develop from the parenchymatous Lngerhans ) develop from the parenchymatous pancreatic tissue.pancreatic tissue.

Insulin secretion begin at approximately the Insulin secretion begin at approximately the fifth month.fifth month.

Glucagon and somatostatin , secreting cells Glucagon and somatostatin , secreting cells also develop from parenchymal cells.also develop from parenchymal cells.

Splanchnic mesoderm surrounding the Splanchnic mesoderm surrounding the pancreatic bud forms the pancreatic connective pancreatic bud forms the pancreatic connective tissue.tissue.

MIDGUTMIDGUT In the fifth week embryo the midgut is In the fifth week embryo the midgut is

suspended from dorsal abdoinal wall by a suspended from dorsal abdoinal wall by a short mesentary, and communicates with yolk short mesentary, and communicates with yolk sac by way of the vitelline duct or yolk stalk.sac by way of the vitelline duct or yolk stalk.

In the adult the midgut begin immediatelly In the adult the midgut begin immediatelly distal to the entrance of bile ductin to the distal to the entrance of bile ductin to the duodenum and and terminate at the junction of duodenum and and terminate at the junction of the proximal two-third of the transverse colon the proximal two-third of the transverse colon with the distal third.with the distal third.

The migut is supplied by the superior The migut is supplied by the superior mesenteric artery.mesenteric artery.

Fig 14.24Fig 14.24

14.2514.25

MIDGUTMIDGUT Development of the midgut is chracterized by rapid Development of the midgut is chracterized by rapid

elongation and of the gut and its mesentery ; resulting elongation and of the gut and its mesentery ; resulting in formation of the primary intestinal loop.in formation of the primary intestinal loop.

The loop remain open connection with the yolk sac The loop remain open connection with the yolk sac by way of the vitelline duct.by way of the vitelline duct.

The cephalic limb develop into ; the distal part of the The cephalic limb develop into ; the distal part of the duodenum, the jejunum, and part of the ileum.duodenum, the jejunum, and part of the ileum.

The caudal limb becomes the lower portion of the The caudal limb becomes the lower portion of the ileum the cecum, appendix, ascending colon, and the ileum the cecum, appendix, ascending colon, and the proximal two-third of the transverse colon.proximal two-third of the transverse colon.

PHYSIOLOGICAL HERNIATIONPHYSIOLOGICAL HERNIATION

Rapid elongation of the loop, rapid growth and Rapid elongation of the loop, rapid growth and expansion of the liver.expansion of the liver.

The intestinal loop enter the extraembryonic The intestinal loop enter the extraembryonic cavity in the umbilical cord during the sixth cavity in the umbilical cord during the sixth week of the development.week of the development.

Fig 14.26Fig 14.26

ROTATION OF THE MIDGUTROTATION OF THE MIDGUT

Around an axis formed by the superior Around an axis formed by the superior mesentetic artery.mesentetic artery.

During herniation about 90During herniation about 90 During return into the abdominal cavity 180.During return into the abdominal cavity 180. During rotation , elongation of the small During rotation , elongation of the small

intestinal loop continues.intestinal loop continues.

RETRACTION OF THE HERNIAL RETRACTION OF THE HERNIAL LOOPSLOOPS

During the 10th week,it is thought due to ;During the 10th week,it is thought due to ; - regression of the mesonephric kidney.- regression of the mesonephric kidney. - reduced growth of the liver.- reduced growth of the liver. - expansion of the abdominal cavity.- expansion of the abdominal cavity. The first part reenter the abdominal cavity is The first part reenter the abdominal cavity is

the proximal part of the jejunum, comesto lie the proximal part of the jejunum, comesto lie on the left side.on the left side.

The last part of the gut reenter the abdominal The last part of the gut reenter the abdominal cavity is the cecum, it appear at the sixth cavity is the cecum, it appear at the sixth week. During this process cecal bud forms week. During this process cecal bud forms appendix.appendix.

Fig 14.27Fig 14.27

Fig 14.28Fig 14.28

Fig 14.29Fig 14.29

MESENTERY OF THE MESENTERY OF THE INTESTINAL LOOPSINTESTINAL LOOPS

When the caudal limb of the loop moves to the When the caudal limb of the loop moves to the right side , the dorsal mesentery twists around right side , the dorsal mesentery twists around the origin of the suprior mesenteric artery.the origin of the suprior mesenteric artery.

When the ascending and descending colon When the ascending and descending colon obtain their definitive position, their obtain their definitive position, their mesenteric press against the peritonium of the mesenteric press against the peritonium of the posterior abdominal wall.posterior abdominal wall.

The transverse mesocolon fuses with the The transverse mesocolon fuses with the posterior wall of the greater omentum.posterior wall of the greater omentum.

Fig 14.30Fig 14.30

ABNORMALITIES OF THE ABNORMALITIES OF THE MESENTERIESMESENTERIES

Persistence of the mesocolon ascendenPersistence of the mesocolon ascenden

- mobile cecum.- mobile cecum.

- volvulus.- volvulus. Incomplete fusion of the mesenteryIncomplete fusion of the mesentery

- retrocolic pocket behind the ascending - retrocolic pocket behind the ascending

colon ---colon ---

retrocolic hernia.retrocolic hernia.

BODY WALL DEFECTBODY WALL DEFECT

OMPHALOCELEOMPHALOCELE - Herniation of abdominal viscera through an - Herniation of abdominal viscera through an enlarged umbilical ring.enlarged umbilical ring. - Viscera ; liver, small and large intestine- Viscera ; liver, small and large intestine dtomach. Gallbladder and spleendtomach. Gallbladder and spleen are covered by amnion.are covered by amnion. - The origin defect is failure of the bowel to - The origin defect is failure of the bowel to return to body cavity from its physiologicalreturn to body cavity from its physiological herniationherniation

BODY WALL DEFECTSBODY WALL DEFECTS

GASTROSCHISISGASTROSCHISIS = A protrusion of the abdominal contents = A protrusion of the abdominal contents through the body wall directly into the through the body wall directly into the amniotic cavity.amniotic cavity. - The defect is most likely due to abnormal - The defect is most likely due to abnormal closure of the body wall around the closure of the body wall around the

connectinconnectin stalk.stalk. - Viscera are not covered by peritonium or - Viscera are not covered by peritonium or amnion.amnion.

VITELLINE DUCT VITELLINE DUCT

GUT ROTATION DEFECTGUT ROTATION DEFECT

GUT ATRESIA AND STENOSISGUT ATRESIA AND STENOSIS

HINDGUTHINDGUT

Hind gut ; distal third of the transverse colon, Hind gut ; distal third of the transverse colon, descending colon,sigmoid colon, rectum and descending colon,sigmoid colon, rectum and upper part of the anal canal.upper part of the anal canal.

The terminal portion of the hindgut enter The terminal portion of the hindgut enter theposterior regioof the cloaca --- primitive theposterior regioof the cloaca --- primitive anorectal.anorectal.

The allantois enter the anterior portion of the The allantois enter the anterior portion of the cloaca ---- primitive urogenital sinus.cloaca ---- primitive urogenital sinus.

HINDGUTHINDGUT The cloaca is an endodermal-lined The cloaca is an endodermal-lined

cavitycovered at its ventral boundary by cavitycovered at its ventral boundary by surface ectoderm.surface ectoderm.

This boundary between the endoderm and the This boundary between the endoderm and the ectoderm forms the cloacal membrane.ectoderm forms the cloacal membrane.

The urorectal septum separates the region The urorectal septum separates the region betwen the allantois and hindgut.betwen the allantois and hindgut.

As the embryo grows, the tip of the urorectal As the embryo grows, the tip of the urorectal septum comes to lie close to the cloacal septum comes to lie close to the cloacal membrane.membrane.

HINDGUTHINDGUT

At the end of the seventh week , the cloacal At the end of the seventh week , the cloacal membrane ruptures membrane ruptures

- opening of the hindgut.- opening of the hindgut.

- opening of the urogenital sinus.- opening of the urogenital sinus. The tip of the urorectal septum form the The tip of the urorectal septum form the

perineal body.perineal body. Proliferation of the ectoderm closes the Proliferation of the ectoderm closes the

caudalmost region of the analcanal.caudalmost region of the analcanal.

HINDGUTHINDGUT

During the ninth week this regio recanalizes.During the ninth week this regio recanalizes. The caudal part of the anal canal originates in The caudal part of the anal canal originates in

the ectoderm, and supplied by the inferior the ectoderm, and supplied by the inferior rectal arteries.rectal arteries.

The cranial part of the anal canal originates in The cranial part of the anal canal originates in the endoderm, and is supplied by the superior the endoderm, and is supplied by the superior rectal artery.rectal artery.

The junction between the endodermal and The junction between the endodermal and ectodermal of the anal canal is the pectinate ectodermal of the anal canal is the pectinate line.line.