Embryology of Digestive system

DEVELOPMENT OF THE DIGESTIVE SYSTEM

Shittu LAJShittu LAJ

OBJECTIVES:

� Able to describe the formation of primitive gut Able to describe the formation of primitive gut from the yolk sac.from the yolk sac.

S Able to List the Derivatives of the foregut, and Able to List the Derivatives of the foregut, and describe the rotation of the stomach and describe the rotation of the stomach and formation of omental bursa (Lesser sac of formation of omental bursa (Lesser sac of peritoneum).peritoneum).

S Able to describe the development of the Able to describe the development of the duodenum, liver, biliary apparatus, pancreas duodenum, liver, biliary apparatus, pancreas and spleen.and spleen.

S Able to list the derivatives of the midgut, Able to list the derivatives of the midgut, describe herniation, rotation, reduction and describe herniation, rotation, reduction and fixation of the midgut.fixation of the midgut.

S Able to list the derivatives of the hindgut. Able to list the derivatives of the hindgut. Describe the partitioning of the cloaca and Describe the partitioning of the cloaca and development of the anal canal.development of the anal canal.

� Describe the congenital abnormalities of the Digestive

Primitive Gut TubePrimitive Gut Tube

� The The primitive gut tubeprimitive gut tube is derived is derived from the dorsal part of the from the dorsal part of the yolk sacyolk sac , ,

� which is incorporated into the body of which is incorporated into the body of the embryo during folding of the the embryo during folding of the embryo during the fourth week. embryo during the fourth week.

� The primitive gut tube is divided into The primitive gut tube is divided into three sections-foregut, midgut and three sections-foregut, midgut and hindguthindgut

� The The epitheliumepithelium of and the of and the parenchyma parenchyma of glandsof glands associated with the digestive associated with the digestive tract (e.g., liver and pancreas) are derived tract (e.g., liver and pancreas) are derived from from endodermendoderm. .

� The The muscular wallsmuscular walls of the digestive tract of the digestive tract (lamina propria, muscularis mucosae, (lamina propria, muscularis mucosae, submucosa, muscularis externa, adventitia submucosa, muscularis externa, adventitia and/or serosa) are derived from and/or serosa) are derived from splanchnic mesodermsplanchnic mesoderm ..

� During the During the solid stagesolid stage of development, of development, the endoderm of the gut tube proliferates the endoderm of the gut tube proliferates until the gut is a solid tube. until the gut is a solid tube.

� However, a process of However, a process of recanalizationrecanalization restores the lumen.restores the lumen.

Primitive Gut

S Forms during the 4Forms during the 4 thth week. week.S Originate from the dorsal part of yolk Originate from the dorsal part of yolk

sac.sac.S Endoderm derivatives - (epithelial Endoderm derivatives - (epithelial

lining)lining)S Mesoderm (Splanchnic or Visceral Mesoderm (Splanchnic or Visceral

LPM) - Connective tissue and other LPM) - Connective tissue and other layers.layers.

Proctodeum and Proctodeum and StomodeumStomodeum

� The proctodeum (anal pit) is the The proctodeum (anal pit) is the primordial anus, and primordial anus, and

� The stomodeum is the primordial mouth. The stomodeum is the primordial mouth. � In both of these areas ectoderm is in direct In both of these areas ectoderm is in direct

contact with endoderm without contact with endoderm without intervening mesoderm, intervening mesoderm,

� There is eventually the degeneration of There is eventually the degeneration of both tissue layers.both tissue layers.

Primitive Digestive Tract Primitive Digestive Tract

The ForegutDerivatives

– The Primitive Pharynx and Respiratory System.

� Esophagus, Stomach and Duodenum (1st part only).

� Liver, Gall Bladder, Bile Duct and Pancreas� Artery: Celiac Artery

EsophagusEsophagus

� The The tracheoesophageal septumtracheoesophageal septum divides the foregut into the esophagus and divides the foregut into the esophagus and trachea. trachea.

StomachStomach

� The primordium of the The primordium of the primitive stomachprimitive stomach is is visible about the end of the visible about the end of the fourth week. fourth week.

� It is initially oriented in the median plane and It is initially oriented in the median plane and suspended from the dorsal wall of the abdominal suspended from the dorsal wall of the abdominal cavity by the cavity by the dorsal mesenterydorsal mesentery or or mesogastriummesogastrium..

� During development the stomach rotates 90During development the stomach rotates 90°° � in a clockwise direction along its longitudinal in a clockwise direction along its longitudinal

axis, placing the axis, placing the left vagus nerveleft vagus nerve along its along its anterior side and the anterior side and the right vagus nerveright vagus nerve along along its posterior side. its posterior side.

� Rotation of the stomach creates the Rotation of the stomach creates the omental omental bursabursa or or lesser peritoneal saclesser peritoneal sac ..

Development of Foregut

S Tracheoesophageal septumTracheoesophageal septumS Recanalization of esophagusRecanalization of esophagusS Median plane dilation in foregutMedian plane dilation in foregut� Rotation of stomach – 90 o clockwisely

Mesenteries of the stomach areMesenteries of the stomach are

� - Dorsal mesogastrium� - Ventral mesogastrium� - Omental bursa, greater omentum

DuodenumDuodenum

� The duodenum acquires its C-shaped The duodenum acquires its C-shaped loop as the stomach rotates. loop as the stomach rotates.

� Because of its location at the junction Because of its location at the junction of the foregut and the midgut, of the foregut and the midgut, branches of both thebranches of both the celiac trunk celiac trunk and the and the superior mesenteric superior mesenteric arteryartery supply the duodenum supply the duodenum . .

The Foregut Organs

S They develop as endodermal diverticulaThey develop as endodermal diverticulaS Pancreatic diverticula, hepatic diverticulaPancreatic diverticula, hepatic diverticulaS Spleen from splanchnic mesoderm with Spleen from splanchnic mesoderm with

dorsal mesenterydorsal mesentery

� The pancreas develops from two outgrowths The pancreas develops from two outgrowths of the endodermal epithelium, of the endodermal epithelium,

� the the dorsal pancreatic buddorsal pancreatic bud and the and the ventral pancreatic budventral pancreatic bud . .

� During rotation of the gut these primordial During rotation of the gut these primordial come together to form a single pancreas. come together to form a single pancreas.

PancreasPancreas

� The ventral pancreatic bud forms the uncinate The ventral pancreatic bud forms the uncinate process and part of the head,process and part of the head,

� while the dorsal pancreatic bud forms the while the dorsal pancreatic bud forms the remainder of the head, body, and tail of the remainder of the head, body, and tail of the pancreas. pancreas.

� The ducts of the pancreatic buds join together The ducts of the pancreatic buds join together to form the to form the main pancreatic ductmain pancreatic duct , ,

� but the proximal part of the duct of the dorsal but the proximal part of the duct of the dorsal pancreatic bud may persist as an pancreatic bud may persist as an accessory accessory pancreatic ductpancreatic duct

SpleenSpleen

� The spleen develops from mesenchymal The spleen develops from mesenchymal cells located between layers of the dorsal cells located between layers of the dorsal mesogastrium.mesogastrium.

Liver and Biliary ApparatusLiver and Biliary Apparatus

� The liver develops from endodermal cells The liver develops from endodermal cells that form the that form the hepatic diverticulumhepatic diverticulum . .

� The liver grows in close association with The liver grows in close association with the the septum transversumseptum transversum , ,

� which later forms part of the diaphragm. which later forms part of the diaphragm. � As it grows the hepatic diverticulum divides As it grows the hepatic diverticulum divides

into a into a cranial partcranial part , which forms the , which forms the parenchymaparenchyma of the liver and of the liver and

� the the caudal partcaudal part , which gives rise to the , which gives rise to the gall-bladdergall-bladder and and cystic ductcystic duct . .

� The The hemopoietichemopoietic cellscells , , Kupffer cellsKupffer cells , , and and connective tissueconnective tissue of the liver are of the liver are derived from derived from mesenchymemesenchyme in the septum in the septum transversum. transversum.

� The embryonic liver is large and fills much of The embryonic liver is large and fills much of the abdominal cavity during the seventh the abdominal cavity during the seventh through ninth weeks of development.through ninth weeks of development.

� Blood formation (hemopoiesisBlood formation (hemopoiesis) ) begins in the begins in the liver during the sixth week of development, liver during the sixth week of development, and bile formation begins in the twelfth week.and bile formation begins in the twelfth week.

MidgutMidgut

� The midgut communicates with the yolk sac The midgut communicates with the yolk sac via the via the yolk stalkyolk stalk . .

� As the midgut forms, it elongates into a U-As the midgut forms, it elongates into a U-shaped loop (shaped loop (midgut loopmidgut loop ) that temporarily ) that temporarily projects into the umbilical cord projects into the umbilical cord ((physiological umbilical herniationphysiological umbilical herniation ). ).

� The cranial limb of the midgut elongates The cranial limb of the midgut elongates rapidly during development and forms the rapidly during development and forms the jejunumjejunum and and cranial portion of the cranial portion of the ileumileum . .

� The caudal limb forms the The caudal limb forms the cecumcecum , , appendixappendix , , caudal portion of the ileumcaudal portion of the ileum , , ascending ascending coloncolon , and , and proximal two-thirds of theproximal two-thirds of the transverse colontransverse colon . .

� The caudal limb is easily recognized during The caudal limb is easily recognized during development because of the presence of the development because of the presence of the cecal diverticulumcecal diverticulum ..

� The midgut loop rotates The midgut loop rotates 270270 °° counter- counter-clockwiseclockwise around the around the superior superior mesenteric arterymesenteric artery as it retracts into the as it retracts into the abdominal cavity during the 10thabdominal cavity during the 10th week week of of development.development.

Section Blood supply Adult derivatives

Foregut Celiac artery

Pharynx, lower respiratory system, esophagus, stomach, proximal half of duodenum, liver and pancreas, biliary apparatus

Midgut Derivatives

� 1.1. Small intestines (most of duodenum) Small intestines (most of duodenum) jejunum, ileumjejunum, ileum

� 2.2. The Caecum, Appendix, Ascending The Caecum, Appendix, Ascending Colon and Transverse Colon (proximal 2/3)Colon and Transverse Colon (proximal 2/3)

S Midgut loops around the axis of SMAMidgut loops around the axis of SMAS Physiological umbilical herniationPhysiological umbilical herniationS Cecal diverticulum (MeckelCecal diverticulum (Meckel==s)s)S Rotation of the Midgut loopRotation of the Midgut loopS Return of Midgut to the AbdomenReturn of Midgut to the Abdomen� (reduction of the midgut hernia)S Fixation of the IntestineFixation of the Intestine� Caecum and Appendix growth

Artery: Superior mesenteric Artery (SMA)

HindgutHindgut

� The hindgut is defined to begin where the The hindgut is defined to begin where the blood supply changes from the superior blood supply changes from the superior mesenteric artery to the mesenteric artery to the inferior inferior mesenteric arterymesenteric artery , i.e. at the distal third of , i.e. at the distal third of the transverse colon.the transverse colon.

Hind GutDerivatives

S Left one-third to half or distal part of the Left one-third to half or distal part of the transverse colontransverse colon

S Descending colonDescending colonS Sigmoid colonSigmoid colonS RectumRectumS Superior portion of the anal canalSuperior portion of the anal canal� Epithelium of the urinary bladder and most

of urethra

hindguthindgut

� Artery: Inferior mesenteric artery� Fixation of hind gut

Section

Blood supply Adult derivatives

Fore-gut

Celiac artery Pharynx, lower respiratory system, esophagus, stomach, proximal half of duodenum, liver and pancreas, biliary apparatus

Mid-gut

Superior mesenteric artery

Small intestine, distal half of duodenum, cecum and vermiform appendix, ascending colon, most of the transverse colon

Hindgut

Inferior mesenteric artery

Left part of transverse colon, descending colon, sigmoid colon, rectum, superior part of anal canal, epithelium of urinary bladder, most of the urethra

Partitioning of the CloacaPartitioning of the Cloaca

� The cloaca is the endodermally lined The cloaca is the endodermally lined cavity at the end of the gut tube. cavity at the end of the gut tube.

� It has a diverticulum into the body stalk It has a diverticulum into the body stalk called the called the allantoisallantois . .

� The The cloacal membranecloacal membrane separates the separates the cloaca from the proctodeum (cloaca from the proctodeum (anal pitanal pit ). ).

� During development , a sheet of During development , a sheet of mesenchyme (mesenchyme (urorectal septumurorectal septum) ) develops to divide the cloaca into a ventral develops to divide the cloaca into a ventral ((urogenital sinusurogenital sinus ) and ) and

� a dorsal portion (a dorsal portion (anorectal canalanorectal canal ). ). � By By 7th week7th week , the , the urorectal septumurorectal septum

reaches the cloacal membrane, dividing it reaches the cloacal membrane, dividing it into : into :

� ventral (ventral (urogenital membraneurogenital membrane ) and ) and � dorsal (dorsal (anal membraneanal membrane ) portions.) portions.

Partitioning of cloacaPartitioning of cloaca

Partitioning of the Cloaca

S Urorectal Septum divides the cloaca into Urorectal Septum divides the cloaca into two divisions.two divisions.

S Divisions- rectal, anal canalDivisions- rectal, anal canal� - urogenital sinus� Perineal Body - Fusion of urorectal septum

and cloaca membrane

Anal CanalAnal Canal

� The epithelium of the superior two-thirds The epithelium of the superior two-thirds of the anal canal is derived from the of the anal canal is derived from the endodermal hindgut; endodermal hindgut;

� the inferior one-third develops from the the inferior one-third develops from the ectodermal proctodeum. ectodermal proctodeum.

� The junction of these two epithelia is The junction of these two epithelia is indicated by the indicated by the pectinate linepectinate line , which , which also indicates the approximate former site also indicates the approximate former site of the of the anal membraneanal membrane that normally that normally ruptures during the 8ruptures during the 8 thth w weekeek of of developmentdevelopment ..

Partitioning of cloacaPartitioning of cloaca

Clinical Embryology

� Esophageal Atresia or Stenosis� (Polyhydramnios, RDS [Respiratory

Distress Syndrome], Surgery)� Congenital Hypertrophic: Pyloric Stenosis� (Projectile vomiting) - Prepyloric vein of

Mayo usual landmark during surgical correction.

� Duodenal Stenosis or Atresia� (Anular pancreas)� Congenital Omphalocele

� Umbilical Hernia� Rotation abnormalities (none rotation,

mixed rotation, volvulus)

� Meckel Diverticulum 2% of population 2" (5 cm) long, 2 ft (60 cm) from the ileocecal junction (2:2:2:)

� Megacolon-congenital

� Imperforate anus

Ileal Diverticulum (Meckel’s Ileal Diverticulum (Meckel’s Diverticulum)Diverticulum)

� A remnant of the proximal part of the A remnant of the proximal part of the yolk stalk that fails to degenerate during yolk stalk that fails to degenerate during the early fetal period results in a finger-the early fetal period results in a finger-like blind pouch that projects from the like blind pouch that projects from the ileum. ileum.

� While this condition occurs in about 1/50 While this condition occurs in about 1/50 people, people,

� it is usually asymptomic and only it is usually asymptomic and only occasionally leads to abdominal pain occasionally leads to abdominal pain and/or rectal bleeding.and/or rectal bleeding.

Esophageal AtresiaEsophageal Atresia

� Esophageal atresiaEsophageal atresia usually results from usually results from abnormal division of the tracheo-esophageal abnormal division of the tracheo-esophageal septum. septum.

� The fetus is unable to swallow andThe fetus is unable to swallow and� this results in this results in polyhydramniospolyhydramnios (excessive (excessive

amount of amniotic fluid) because amniotic amount of amniotic fluid) because amniotic fluid cannot pass into the intestines for fluid cannot pass into the intestines for return to the maternal circulation.return to the maternal circulation.

Congenital Hypertrophic Pyloric StenosisCongenital Hypertrophic Pyloric Stenosis

� Overgrowth of the longitudinal muscle fibers of Overgrowth of the longitudinal muscle fibers of the pylorus creates a marked thickening of the the pylorus creates a marked thickening of the pyloric region of the stomach. pyloric region of the stomach.

� The resulting stenosis (Gk. severe narrowing) of The resulting stenosis (Gk. severe narrowing) of the pyloric canal obstructs passage of food into the pyloric canal obstructs passage of food into the duodenum, and the duodenum, and

� as a result after feeding the infant expels the as a result after feeding the infant expels the contents of the stomach with considerable force contents of the stomach with considerable force (projectile vomiting). (projectile vomiting).

� This condition affects approximately 1/150 male This condition affects approximately 1/150 male infants, but only 1/750 female infants.infants, but only 1/750 female infants.

Annular PancreasAnnular Pancreas

� The ventral and dorsal pancreatic buds The ventral and dorsal pancreatic buds form a ring around the duodenum, thereby form a ring around the duodenum, thereby obstructing it. obstructing it.

OmphaloceleOmphalocele

� The midgut fails to retract into the The midgut fails to retract into the abdominal cavity. abdominal cavity.

� At birth, coils of intestine covered with only a At birth, coils of intestine covered with only a transparent sac of amniontransparent sac of amnion protrude protrude from the umbilicus. from the umbilicus.

Malrotations of the MidgutMalrotations of the Midgut� The midgut does not rotate normally as it The midgut does not rotate normally as it

retracts into the abdominal cavity. retracts into the abdominal cavity. � This usually presents as symptoms of This usually presents as symptoms of

intestinal obstruction shortly after birth. intestinal obstruction shortly after birth. � Malrotation also predisposes the infant to a Malrotation also predisposes the infant to a

volvulus of the midgutvolvulus of the midgut , wherein the , wherein the intestines bind and twist around a short intestines bind and twist around a short mesentery. mesentery.

� Volvulus usually interferes with the blood Volvulus usually interferes with the blood supply to a section of the intestines, and can supply to a section of the intestines, and can lead to necrosis and gangrene.lead to necrosis and gangrene.

Sub-hepatic Cecum and Sub-hepatic Cecum and AppendixAppendix

� The cecum and appendix adhere to the The cecum and appendix adhere to the inferior surface of the liver during the fetal inferior surface of the liver during the fetal period, and period, and

� are carried upwards with it, resulting in an are carried upwards with it, resulting in an abnormal anatomical position that may abnormal anatomical position that may create difficulties in diagnosing create difficulties in diagnosing appendicitis.appendicitis.

Stenosis and Atresia of the Small IntestineStenosis and Atresia of the Small Intestine

� Failure of recanalization of ileum during the Failure of recanalization of ileum during the solid stage of development leads to solid stage of development leads to

� stenosis (narrowing) or stenosis (narrowing) or � atresia (complete obstruction) of the atresia (complete obstruction) of the

intestinal lumen. intestinal lumen. � Some stenoses and atresias may be caused Some stenoses and atresias may be caused

by an infarction of the fetal bowel owing to by an infarction of the fetal bowel owing to impairment of its blood supply (cf. volvulus).impairment of its blood supply (cf. volvulus).

Congenital Aganglionic Megacolon (Hirschsprung’s Congenital Aganglionic Megacolon (Hirschsprung’s disease)disease)

� This results from the failure of neural crest This results from the failure of neural crest cells to migrate and form the myenteric cells to migrate and form the myenteric plexus in the sigmoid colon and rectum. plexus in the sigmoid colon and rectum.

� The resulting lack of innervation results in:The resulting lack of innervation results in:� loss of peristalsis, loss of peristalsis, � fecal retention, and fecal retention, and � abdominal distention.abdominal distention.

Anorectal AgenesisAnorectal Agenesis

� Abnormal formation of the urorectal Abnormal formation of the urorectal septum causes the rectum to end as a blind septum causes the rectum to end as a blind sac above the puborectalis muscle.sac above the puborectalis muscle.

Anal AgenesisAnal Agenesis

� Abnormal formation of the urorectal Abnormal formation of the urorectal septum causes the rectum to end as a blind septum causes the rectum to end as a blind sac below the puborectalis muscle.sac below the puborectalis muscle.

Imperforate AnusImperforate Anus

� The anal membrane fails to break down The anal membrane fails to break down before birth. before birth.

� The anus must be reconstructed surgically, The anus must be reconstructed surgically, with severity depending on the thickness of with severity depending on the thickness of the intervening tissue.the intervening tissue.

Embryology of Digestive system

Health & Medicine

Transcript of Embryology of Digestive system