The Development of the The Development of the Digestive System Digestive System

Dr. Zeenat Zaidi

The Primitive GutThe Primitive Gut The The endodermendoderm of the of the

primordial gut gives rise primordial gut gives rise to most of the to most of the epithelium epithelium and and glandsglands of the of the digestive tractdigestive tract

The The musclesmuscles, , connective connective tissuetissue and other layers of and other layers of the wall of the tract are the wall of the tract are derived from the derived from the splanchnic mesoderm splanchnic mesoderm

Stomodeum Proctodeum

Each part of the developing Each part of the developing gut receives a branch of the gut receives a branch of the aorta: aorta: Celiac trunkCeliac trunk supplies the supplies the

foregutforegut & its derivatives & its derivatives Superior mesenteric Superior mesenteric

arteryartery supplies the supplies the midgutmidgut & its derivatives & its derivatives

Inferior mesenteric Inferior mesenteric arteryartery supplies the supplies the hindguthindgut & its derivatives & its derivatives

The Foregut DerivativesThe Foregut Derivatives

Development of the Development of the respiratory diverticulum respiratory diverticulum from the floor of the from the floor of the foregut, divideds the foregut, divideds the foregut into two parts: foregut into two parts:

Part Part cranialcranial to to diverticulum is the diverticulum is the primitive pharynxprimitive pharynx

Part Part caudalcaudal to to diverticulum is the diverticulum is the foregut properforegut proper

Primitive pharynx

Foregut proper

The Foregut DerivativesThe Foregut Derivatives Primordial pharynx and its derivativesPrimordial pharynx and its derivatives Lower respiratory tract (larynx, trachea, Lower respiratory tract (larynx, trachea,

bronchi & lungs)bronchi & lungs) Derivatives of foregut properDerivatives of foregut proper::

EsophagusEsophagus StomachStomach Proximal half of duodenumProximal half of duodenum Liver & biliary apparatusLiver & biliary apparatus Pancreas Pancreas

Development of the Development of the EsophagusEsophagus

Esophagus develops from the foregut immediately caudal to the primitive pharynx

The tracheo-esophageal septum separates it from the developing trachea

Initially short in length, elongates rapidly due to growth and descent of heart and lungs

Reaches its final relative length by 7th week

The epithelial cells The epithelial cells proliferate and proliferate and obliterate the lumen obliterate the lumen (partly or completely) (partly or completely) but but temporarilytemporarily

RecanalizationRecanalization normally normally occurs by the occurs by the end of the end of the embryonic periodembryonic period

Failure of proper Failure of proper recanalization leads to recanalization leads to narrowing of the lumen narrowing of the lumen ((stenosisstenosis))

Epithelium & glandsEpithelium & glands: : Derived from Derived from endodermendoderm

Striated muscles Striated muscles (mainly in the (mainly in the superior third): superior third): Derived from the mesenchyme in the Derived from the mesenchyme in the

caudal caudal pharyngeal achespharyngeal aches Smooth muscles (mainly in the inferior (mainly in the inferior

third): third): Derived from the surrounding Derived from the surrounding

splanchnic mesodermsplanchnic mesoderm

Development of the StomacDevelopment of the Stomachh In the middle of the In the middle of the fourth week, fourth week,

aa fusiform dilatationfusiform dilatation appears in appears in the caudal part of the foregut that the caudal part of the foregut that indicates the site of future indicates the site of future stomachstomach

The dilatation oriented in the The dilatation oriented in the midline, enlarges and broadens midline, enlarges and broadens ventrodorsallyventrodorsally

During next 2 weeks:During next 2 weeks: The The dorsal border dorsal border grows much grows much

faster and forms the faster and forms the greater greater curvaturecurvature

The The ventral border ventral border forms the forms the lesser lesser curvaturecurvature

As a result, the:As a result, the: The ventral border moves to The ventral border moves to

the rightthe right and the dorsal border and the dorsal border to the leftto the left

The right side becomes the The right side becomes the dorsal surface dorsal surface and the left side and the left side becomes the ventral surfacebecomes the ventral surface

As stomach enlarges, it slowly rotates 90 degrees, clockwise around its longitudinal axis

Initially the two ends of the Initially the two ends of the stomach lie in the midline. stomach lie in the midline. During rotation:During rotation: the cranial end moves to the cranial end moves to

the left and slightly the left and slightly ventrallyventrally

the caudal end moves to the caudal end moves to the right and dorsallythe right and dorsally

After rotation, stomach After rotation, stomach assumes its final position assumes its final position with its long axis almost with its long axis almost transverse to the long axis transverse to the long axis of the bodyof the body

Omental Bursa (Lesser Sac)Omental Bursa (Lesser Sac) Begins as small isolated clefts Begins as small isolated clefts

in the in the dorsal mesogastriumdorsal mesogastrium, , that soon join to form a single that soon join to form a single cavitycavity

Rotation of stomach pulls the Rotation of stomach pulls the dorsal mesogastrium to the dorsal mesogastrium to the left thus enlarging the cavityleft thus enlarging the cavity

The bursa expands The bursa expands transversely and cranially and transversely and cranially and lies between the stomach and lies between the stomach and the posterior abdominal wallthe posterior abdominal wall

The The superior partsuperior part of the bursa of the bursa is cut off as the diaphragm is cut off as the diaphragm develops. Inferiorly it persists develops. Inferiorly it persists as the as the superior recesssuperior recess of the of the omental bursaomental bursa

The The inferior partinferior part grows within grows within the 4-layered greater omentum the 4-layered greater omentum forming the forming the inferior recessinferior recess of of the omental bursa the omental bursa

The inferior recess later on The inferior recess later on closes down because of fusion closes down because of fusion of the layers of the greater of the layers of the greater omentumomentum

Inferior recess

Development of the Development of the DuodenumDuodenum

Duodenum begins to develop early in Duodenum begins to develop early in 44thth week, week, from the from the caudal part of the foregut and cranial part of the midgutcaudal part of the foregut and cranial part of the midgut

Grows rapidly, forms a C-shaped loop that projects Grows rapidly, forms a C-shaped loop that projects ventrallyventrally

Rotation of stomach pulls it to the right and dorsally, Rotation of stomach pulls it to the right and dorsally, bringing it in a bringing it in a retro-peritoneal positionretro-peritoneal position

During During 5-65-6thth weeks weeks, its lumen obliterates due to , its lumen obliterates due to proliferation of epithelial cellsproliferation of epithelial cells

Recanalization is complete by the end of embryonic Recanalization is complete by the end of embryonic periodperiod

Most of the ventral mesentery disappears by this time Most of the ventral mesentery disappears by this time

Development of the LiverDevelopment of the Liver Liver appears in Liver appears in 44thth week week, ,

as a ventral bud called as a ventral bud called hepatic diverticulumhepatic diverticulum, , from the caudal part of from the caudal part of the foregutthe foregut

The bud grows into the The bud grows into the septum transversumseptum transversum (which is forming the (which is forming the ventral mesentery in this ventral mesentery in this region) and divides into region) and divides into two partstwo parts

The larger The larger cranial partcranial part is is primordium of liver, the primordium of liver, the smaller smaller caudal partcaudal part gives rise gives rise to the gall bladder and cystic to the gall bladder and cystic ductduct

The The endodermal cells endodermal cells of the of the hepatic bud proliferate and hepatic bud proliferate and give rise to give rise to hepatic cordshepatic cords and and the the epithelial liningepithelial lining of the of the intrahepatic portion of the intrahepatic portion of the biliary systembiliary system

The hepatic cords anastomose The hepatic cords anastomose around the around the sinusoidssinusoids derived derived from the vitelline veinsfrom the vitelline veins

The liver grows rapidly The liver grows rapidly and in and in 5-105-10thth weeks weeks fills fills a large part of the a large part of the abdominal cavityabdominal cavity

By By 99thth week week, the liver , the liver forms about 10% of forms about 10% of total body weight total body weight

Initially the right and Initially the right and left lobes are of the left lobes are of the same size, later right same size, later right lobe grows largerlobe grows larger

TheThe hepatic cords hepatic cords and the and the epithelial liningepithelial lining of the of the intrahepatic portion of the biliary systemintrahepatic portion of the biliary system are are derived from derived from endodermendoderm

The The fibrous tissuefibrous tissue, , hematopoeitic tissuehematopoeitic tissue and and Kupffer cellsKupffer cells are derived from the are derived from the mesenchymemesenchyme of of the septum transversumthe septum transversum

The The hepatic sinusoides hepatic sinusoides derived from derived from vitelline veinsvitelline veins Hematopoeisis begins during Hematopoeisis begins during 66thth week week, giving dark , giving dark

color to livercolor to liver The hepatic cells begins to form bile during the The hepatic cells begins to form bile during the 1212thth

weekweek

Development of the Biliary Development of the Biliary ApparatusApparatus

The small caudal part of The small caudal part of the hepatic diverticulum the hepatic diverticulum becomes the becomes the gall bladdergall bladder, , and the stalk of the and the stalk of the diverticulum forms the diverticulum forms the cystic ductcystic duct

The stalk connecting the The stalk connecting the hepatic & cystic ducts to hepatic & cystic ducts to the duodenum becomes the duodenum becomes the the bile ductbile duct, and opens on , and opens on the the ventral aspect of the ventral aspect of the duodenumduodenum. .

Later due to rotation Later due to rotation of duodenum, the of duodenum, the opening comes to lie opening comes to lie dorsallydorsally

The ducts become The ducts become occluded initially, but occluded initially, but are later canalizedare later canalized

After After 1313thth week week, bile , bile entering the duodenum entering the duodenum gives a dark green gives a dark green color to the intestinal color to the intestinal contents (contents (meconiummeconium) )

Development of the Development of the PancreasPancreas

Pancreas begins to appears Pancreas begins to appears asas two two buds, buds, dorsaldorsal and and ventralventral, from the caudal part , from the caudal part of the foregut (region of the foregut (region developing into duodenum) developing into duodenum) that grow within the that grow within the dorsal dorsal and ventral mesenteriesand ventral mesenteries respectivelyrespectively

The The dorsal buddorsal bud is is largerlarger, , appears appears firstfirst and lies and lies cranialcranial to the smaller ventral budto the smaller ventral bud

The rotation of stomach The rotation of stomach and duodenum carry the and duodenum carry the ventral bud dorsally along ventral bud dorsally along with the bile duct. with the bile duct.

The ventral bud comes to The ventral bud comes to lie posterior to the dorsal lie posterior to the dorsal bud and later fuses with it bud and later fuses with it and their ducts and their ducts anastomose anastomose

The The duct of ventral budduct of ventral bud and and distal part of the duct of the distal part of the duct of the dorsal bud dorsal bud form the form the main main pancreatic ductpancreatic duct that opens that opens on the on the major duodenal major duodenal papillapapilla

The The proximal part of the proximal part of the duct of the dorsal budduct of the dorsal bud often often persists as the persists as the accessory accessory pancreatic duct pancreatic duct that opens that opens separately on the separately on the minor minor duodenal papilla duodenal papilla

The The dorsal buddorsal bud forms forms most of the panmost of the pancreascreas

The The ventral budventral bud gives gives rise to the rise to the uncinate uncinate processprocess and and part of the part of the head of the pancreashead of the pancreas

Finally pancreas Finally pancreas comes to lie comes to lie horizontally along the horizontally along the posterior abdominal posterior abdominal wall in a wall in a retroperitoneal retroperitoneal positionposition

Histogenesis of PancreasHistogenesis of Pancreas Parenchyma develops from Parenchyma develops from endodermendoderm of the buds which of the buds which

forms a network of tubulesforms a network of tubules Acini Acini begin to develop early in the begin to develop early in the fetal periodfetal period from cell from cell

clusters around the ends of these tubulesclusters around the ends of these tubules Some cells get separated from the tubules and form the Some cells get separated from the tubules and form the

pancreatic isletspancreatic islets The The connective tissue sheathconnective tissue sheath and and interlobular septaeinterlobular septae

develop from the surrounding develop from the surrounding splanchnic mesenchymesplanchnic mesenchyme Glucagon and somatostatin secreting cells differentiate Glucagon and somatostatin secreting cells differentiate

before the insulin secreting cellsbefore the insulin secreting cells Insulin secretion begins by Insulin secretion begins by 10 weeks10 weeks

Development of the SpleenDevelopment of the Spleen Spleen develops from the Spleen develops from the

mesenchymemesenchyme within the within the dorsal dorsal mesogastriummesogastrium

Begins to develop in Begins to develop in 55thth week week and and attains its shape early in fetal lifeattains its shape early in fetal life

Is lobulated initially but lobules Is lobulated initially but lobules normally disappear before birthnormally disappear before birth

Spleen functions as a Spleen functions as a hematopoeitic organhematopoeitic organ until late until late fetal life, but retains its potential fetal life, but retains its potential for blood cell formation even in for blood cell formation even in adult lifeadult life

Derivatives of the Mesenteries of the Derivatives of the Mesenteries of the ForegutForegut

Dorsal MesoesophagusDorsal Mesoesophagus:: Crura of the Crura of the diaphragmdiaphragm

Ventral Mesoesophagus:Ventral Mesoesophagus: disappears disappears completelycompletely

Dorsal MesogastriumDorsal Mesogastrium:: Lienorenal ligamentLienorenal ligament Gastrosplenic ligamentGastrosplenic ligament

Ventral MesogastriumVentral Mesogastrium:: Lesser omentumLesser omentum Visceral peritoneum of the liverVisceral peritoneum of the liver Falciform ligament of the liverFalciform ligament of the liver

Dorsal mesentery of the duodenumDorsal mesentery of the duodenum: : persists in the proximal part (one inch) as persists in the proximal part (one inch) as hepatoduodenal ligamenthepatoduodenal ligament

Ventral mesentery of the duodenumVentral mesentery of the duodenum: : disappears almost completelydisappears almost completely

Anomalies Related to the Anomalies Related to the Development of the ForegutDevelopment of the Foregut

Tracheo-esophageal fistulaTracheo-esophageal fistula Esophageal atresiaEsophageal atresia may result in may result in

polyhydramniospolyhydramnios Esophageal stenosisEsophageal stenosis usually usually

involves the distal segmentinvolves the distal segment Short esophagusShort esophagus: may give rise to : may give rise to

hiatus hernia hiatus hernia Congenital hypertrophic pyloric Congenital hypertrophic pyloric

stenosisstenosis Variations in the shape of stomachVariations in the shape of stomach Malrotation of stomachMalrotation of stomach Duodenal stenosisDuodenal stenosis Duodenal atresiaDuodenal atresia

Anomalies Related to the Anomalies Related to the Development of the Liver & Gall Development of the Liver & Gall

BladderBladder Anomalies of liver are rare.Anomalies of liver are rare. Variations in hepatic ducts, Variations in hepatic ducts,

cystic and bile ducts are cystic and bile ducts are common and clinically common and clinically significantsignificant

Extrahepatic biliaryExtrahepatic biliary atresia atresia is the most common serious is the most common serious anomaly. Jaundice develops anomaly. Jaundice develops soon after birth. If soon after birth. If uncorrected surgically leads uncorrected surgically leads to deathto death

Anomalies Related to the Anomalies Related to the Development of the Pancreas & Development of the Pancreas &

SpleenSpleen

Accessory pancreatic Accessory pancreatic tissuetissue

Annular pancreasAnnular pancreas Accessory splenic tissueAccessory splenic tissue