The document describes the development of the primitive digestive system from the yolk sac in three main sections - the foregut, midgut, and hindgut. Key points include: - The primitive gut tube is divided into the foregut, midgut, and hindgut, which develop from the endoderm and mesoderm. - The foregut develops into parts of the pharynx, esophagus, stomach, duodenum, liver, gallbladder, pancreas and spleen. The stomach rotates during development. - The midgut forms a U-shaped loop that projects into the umbilical cord before developing into parts of the small intestine.

1. DEVELOPMENT OF THE
DIGESTIVE SYSTEM
Shittu LAJShittu LAJ

2. OBJECTIVES:
Able to describe the formation of primitive gutAble to describe the formation of primitive gut
from the yolk sac.from the yolk sac.
S Able to List the Derivatives of the foregut, andAble to List the Derivatives of the foregut, and
describe the rotation of the stomach anddescribe the rotation of the stomach and
formation of omental bursa (Lesser sac offormation of omental bursa (Lesser sac of
peritoneum).peritoneum).

3. S Able to describe the development of theAble to describe the development of the
duodenum, liver, biliary apparatus, pancreasduodenum, 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 anddescribe 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 andDescribe the partitioning of the cloaca and
development of the anal canal.development of the anal canal.

4. Describe the congenital abnormalities of
the Digestive

5. Primitive Gut TubePrimitive Gut Tube
TheThe primitive gut tubeprimitive gut tube is derivedis derived
from the dorsal part of thefrom the dorsal part of the yolk sacyolk sac,,
which is incorporated into the body ofwhich is incorporated into the body of
the embryo during folding of thethe embryo during folding of the
embryo during the fourth week.embryo during the fourth week.
The primitive gut tube is divided intoThe primitive gut tube is divided into
three sections-foregut, midgut andthree sections-foregut, midgut and
hindguthindgut

6. TheThe epitheliumepithelium of and theof and the parenchymaparenchyma
of glandsof glands associated with the digestiveassociated with the digestive
tract (e.g., liver and pancreas) are derivedtract (e.g., liver and pancreas) are derived
fromfrom endodermendoderm..
TheThe muscular wallsmuscular walls of the digestive tractof the digestive tract
(lamina propria, muscularis mucosae,(lamina propria, muscularis mucosae,
submucosa, muscularis externa, adventitiasubmucosa, muscularis externa, adventitia
and/or serosa) are derived fromand/or serosa) are derived from
splanchnic mesodermsplanchnic mesoderm..
During theDuring the solid stagesolid stage of development,of development,
the endoderm of the gut tube proliferatesthe endoderm of the gut tube proliferates
until the gut is a solid tube.until the gut is a solid tube.
However, a process ofHowever, a process of recanalizationrecanalization
restores the lumen.restores the lumen.

7. Primitive Gut
S Forms during the 4Forms during the 4thth
week.week.
S Originate from the dorsal part of yolkOriginate from the dorsal part of yolk
sac.sac.
S Endoderm derivatives - (epithelialEndoderm derivatives - (epithelial
lining)lining)
S Mesoderm (Splanchnic or VisceralMesoderm (Splanchnic or Visceral
LPM) - Connective tissue and otherLPM) - Connective tissue and other
layers.layers.

9. Proctodeum andProctodeum and
StomodeumStomodeum
The proctodeum (anal pit) is theThe proctodeum (anal pit) is the
primordial anus, andprimordial anus, and
The stomodeum is the primordial mouth.The stomodeum is the primordial mouth.
In both of these areas ectoderm is in directIn both of these areas ectoderm is in direct
contact with endoderm withoutcontact with endoderm without
intervening mesoderm,intervening mesoderm,
There is eventually the degeneration ofThere is eventually the degeneration of
both tissue layers.both tissue layers.

11. Primitive Digestive TractPrimitive Digestive Tract

12. The Foregut
Derivatives
– The Primitive Pharynx and Respiratory System.
Esophagus, Stomach and Duodenum (1st
part
only).
Liver, Gall Bladder, Bile Duct and Pancreas
Artery: Celiac Artery

13. Primitive Digestive TractPrimitive Digestive Tract

14. EsophagusEsophagus
TheThe tracheoesophageal septumtracheoesophageal septum
divides the foregut into the esophagus anddivides the foregut into the esophagus and
trachea.trachea.

15. StomachStomach
The primordium of theThe primordium of the primitive stomachprimitive stomach isis
visible about the end of thevisible about the end of the fourth week.fourth week.
It is initially oriented in the median plane andIt is initially oriented in the median plane and
suspended from the dorsal wall of the abdominalsuspended from the dorsal wall of the abdominal
cavity by thecavity by the dorsal mesenterydorsal mesentery oror
mesogastriummesogastrium..
During development the stomach rotates 90During development the stomach rotates 90°°
in a clockwise direction along its longitudinalin a clockwise direction along its longitudinal
axis, placing theaxis, placing the left vagus nerveleft vagus nerve along itsalong its
anterior side and theanterior side and the right vagus nerveright vagus nerve alongalong
its posterior side.its posterior side.
Rotation of the stomach creates theRotation of the stomach creates the omentalomental
bursabursa oror lesser peritoneal saclesser peritoneal sac ..

16. Development of Foregut
S Tracheoesophageal septumTracheoesophageal septum
S Recanalization of esophagusRecanalization of esophagus
S Median plane dilation in foregutMedian plane dilation in foregut
Rotation of stomach – 90 o clockwisely

17. Mesenteries of the stomach areMesenteries of the stomach are
- Dorsal mesogastrium
- Ventral mesogastrium
- Omental bursa, greater omentum

18. DuodenumDuodenum
The duodenum acquires its C-shapedThe duodenum acquires its C-shaped
loop as the stomach rotates.loop as the stomach rotates.
Because of its location at the junctionBecause 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 trunkceliac trunk
and theand the superior mesentericsuperior mesenteric
arteryartery supply the duodenumsupply the duodenum..

19. Primitive Digestive TractPrimitive Digestive Tract

20. The Foregut Organs
S They develop as endodermal diverticulaThey develop as endodermal diverticula
S Pancreatic diverticula, hepatic diverticulaPancreatic diverticula, hepatic diverticula
S Spleen from splanchnic mesoderm withSpleen from splanchnic mesoderm with
dorsal mesenterydorsal mesentery

21. The pancreas develops from two outgrowthsThe pancreas develops from two outgrowths
of the endodermal epithelium,of the endodermal epithelium,
thethe dorsal pancreatic buddorsal pancreatic bud and theand the
ventral pancreatic budventral pancreatic bud ..
During rotation of the gut these primordialDuring rotation of the gut these primordial
come together to form a single pancreas.come together to form a single pancreas.
PancreasPancreas

22. Primitive Digestive TractPrimitive Digestive Tract

23. The ventral pancreatic bud forms the uncinateThe ventral pancreatic bud forms the uncinate
process and part of the head,process and part of the head,
while the dorsal pancreatic bud forms thewhile the dorsal pancreatic bud forms the
remainder of the head, body, and tail of theremainder of the head, body, and tail of the
pancreas.pancreas.
The ducts of the pancreatic buds join togetherThe ducts of the pancreatic buds join together
to form theto form the main pancreatic ductmain pancreatic duct ,,
but the proximal part of the duct of the dorsalbut the proximal part of the duct of the dorsal
pancreatic bud may persist as anpancreatic bud may persist as an accessoryaccessory
pancreatic ductpancreatic duct

24. SpleenSpleen
The spleen develops from mesenchymalThe spleen develops from mesenchymal
cells located between layers of the dorsalcells located between layers of the dorsal
mesogastrium.mesogastrium.

25. Liver and Biliary ApparatusLiver and Biliary Apparatus
The liver develops from endodermal cellsThe liver develops from endodermal cells
that form thethat form the hepatic diverticulumhepatic diverticulum..
The liver grows in close association withThe liver grows in close association with
thethe septum transversumseptum transversum,,
which later forms part of the diaphragm.which later forms part of the diaphragm.
As it grows the hepatic diverticulum dividesAs it grows the hepatic diverticulum divides
into ainto a cranial partcranial part, which forms the, which forms the
parenchymaparenchyma of the liver andof the liver and
thethe caudal partcaudal part, which gives rise to the, which gives rise to the
gall-bladdergall-bladder andand cystic ductcystic duct..

26. Primitive Digestive TractPrimitive Digestive Tract

27. TheThe hemopoietichemopoietic cellscells,, Kupffer cellsKupffer cells,,
andand connective tissueconnective tissue of the liver areof the liver are
derived fromderived from mesenchymemesenchyme in the septumin the septum
transversum.transversum.
The embryonic liver is large and fills much ofThe embryonic liver is large and fills much of
the abdominal cavity during the sevenththe abdominal cavity during the seventh
through ninth weeks of development.through ninth weeks of development.
Blood formation (hemopoiesisBlood formation (hemopoiesis)) begins in thebegins 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.

28. MidgutMidgut
The midgut communicates with the yolk sacThe midgut communicates with the yolk sac
via thevia 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 cordprojects into the umbilical cord
((physiological umbilical herniationphysiological umbilical herniation ).).
The cranial limb of the midgut elongatesThe cranial limb of the midgut elongates
rapidly during development and forms therapidly during development and forms the
jejunumjejunum andand cranial portion of thecranial portion of the

29. Primitive Digestive TractPrimitive Digestive Tract

30. The caudal limb forms theThe caudal limb forms the cecumcecum,, appendixappendix,,
caudal portion of the ileumcaudal portion of the ileum ,, ascendingascending
coloncolon, and, and proximal two-thirds of theproximal two-thirds of the
transverse colontransverse colon..
The caudal limb is easily recognized duringThe caudal limb is easily recognized during
development because of the presence of thedevelopment because of the presence of the
cecal diverticulumcecal diverticulum ..
The midgut loop rotatesThe midgut loop rotates 270270°° counter-counter-
clockwiseclockwise around thearound the superiorsuperior
mesenteric arterymesenteric artery as it retracts into theas it retracts into the
abdominal cavity during the 10thabdominal cavity during the 10th weekweek ofof
development.development.

31. Section Blood supply Adult derivatives
Foregut Celiac
artery
Pharynx, lower
respiratory system,
esophagus, stomach,
proximal half of
duodenum, liver and
pancreas, biliary
apparatus

32. Midgut
Derivatives
1.1. Small intestines (most of duodenum)Small intestines (most of duodenum)
jejunum, ileumjejunum, ileum
2.2. The Caecum, Appendix, AscendingThe Caecum, Appendix, Ascending
Colon and Transverse Colon (proximal 2/3)Colon and Transverse Colon (proximal 2/3)

34. S Midgut loops around the axis of SMAMidgut loops around the axis of SMA
S Physiological umbilical herniationPhysiological umbilical herniation
S Cecal diverticulum (MeckelCecal diverticulum (Meckel==s)s)
S Rotation of the Midgut loopRotation of the Midgut loop
S 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)

35. HindgutHindgut
The hindgut is defined to begin where theThe hindgut is defined to begin where the
blood supply changes from the superiorblood supply changes from the superior
mesenteric artery to themesenteric artery to the inferiorinferior
mesenteric arterymesenteric artery , i.e. at the distal third of, i.e. at the distal third of
the transverse colon.the transverse colon.

36. Primitive Digestive TractPrimitive Digestive Tract

37. Hind Gut
Derivatives
S Left one-third to half or distal part of theLeft one-third to half or distal part of the
transverse colontransverse colon
S Descending colonDescending colon
S Sigmoid colonSigmoid colon
S RectumRectum
S Superior portion of the anal canalSuperior portion of the anal canal
Epithelium of the urinary bladder and most
of urethra

38. hindguthindgut
Artery: Inferior mesenteric artery
Fixation of hind gut

40. Secti
on
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
Hindg
ut
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

41. Partitioning of the CloacaPartitioning of the Cloaca
The cloaca is the endodermally linedThe 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 stalkIt has a diverticulum into the body stalk
called thecalled the allantoisallantois..
TheThe cloacal membranecloacal membrane separates theseparates the
cloaca from the proctodeum (cloaca from the proctodeum (anal pitanal pit).).

42. Primitive Digestive TractPrimitive Digestive Tract

43. During development , a sheet ofDuring development , a sheet of
mesenchyme (mesenchyme (urorectal septumurorectal septum))
develops to divide the cloaca into a ventraldevelops to divide the cloaca into a ventral
((urogenital sinusurogenital sinus) and) and
a dorsal portion (a dorsal portion (anorectal canalanorectal canal).).
ByBy 7th week7th week, the, the urorectal septumurorectal septum
reaches the cloacal membrane, dividing itreaches the cloacal membrane, dividing it
into :into :
ventral (ventral (urogenital membraneurogenital membrane) and) and
dorsal (dorsal (anal membraneanal membrane) portions.) portions.

44. Partitioning of cloacaPartitioning of cloaca

45. Partitioning of the Cloaca
S Urorectal Septum divides the cloaca intoUrorectal 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

46. Anal CanalAnal Canal
The epithelium of the superior two-thirdsThe epithelium of the superior two-thirds
of the anal canal is derived from theof the anal canal is derived from the
endodermal hindgut;endodermal hindgut;
the inferior one-third develops from thethe inferior one-third develops from the
ectodermal proctodeum.ectodermal proctodeum.
The junction of these two epithelia isThe junction of these two epithelia is
indicated by theindicated by the pectinate linepectinate line, which, which
also indicates the approximate former sitealso indicates the approximate former site
of theof the anal membraneanal membrane that normallythat normally
ruptures during the 8ruptures during the 8thth
wweekeek ofof
developmentdevelopment..

47. Partitioning of cloacaPartitioning of cloaca

48. 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.

49. Duodenal Stenosis or Atresia
(Anular pancreas)
Congenital Omphalocele
Umbilical Hernia
Rotation abnormalities (none rotation,
mixed rotation, volvulus)

50. Meckel Diverticulum 2% of population 2"
(5 cm) long, 2 ft (60 cm) from the
ileocecal junction (2:2:2:)
Megacolon-congenital
Imperforate anus

51. Ileal Diverticulum (Meckel’sIleal Diverticulum (Meckel’s
Diverticulum)Diverticulum)
A remnant of the proximal part of theA remnant of the proximal part of the
yolk stalk that fails to degenerate duringyolk 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 thelike blind pouch that projects from the
ileum.ileum.
While this condition occurs in about 1/50While this condition occurs in about 1/50
people,people,
it is usually asymptomic and onlyit is usually asymptomic and only
occasionally leads to abdominal painoccasionally leads to abdominal pain
and/or rectal bleeding.and/or rectal bleeding.

52. Esophageal AtresiaEsophageal Atresia
Esophageal atresiaEsophageal atresia usually results fromusually results from
abnormal division of the tracheo-esophagealabnormal division of the tracheo-esophageal
septum.septum.
The fetus is unable to swallow andThe fetus is unable to swallow and
this results inthis results in polyhydramniospolyhydramnios (excessive(excessive
amount of amniotic fluid) because amnioticamount of amniotic fluid) because amniotic
fluid cannot pass into the intestines forfluid cannot pass into the intestines for
return to the maternal circulation.return to the maternal circulation.

53. Congenital Hypertrophic Pyloric StenosisCongenital Hypertrophic Pyloric Stenosis
Overgrowth of the longitudinal muscle fibers ofOvergrowth of the longitudinal muscle fibers of
the pylorus creates a marked thickening of thethe pylorus creates a marked thickening of the
pyloric region of the stomach.pyloric region of the stomach.
The resulting stenosis (Gk. severe narrowing) ofThe resulting stenosis (Gk. severe narrowing) of
the pyloric canal obstructs passage of food intothe pyloric canal obstructs passage of food into
the duodenum, andthe duodenum, and
as a result after feeding the infant expels theas a result after feeding the infant expels the
contents of the stomach with considerable forcecontents of the stomach with considerable force
(projectile vomiting).(projectile vomiting).
This condition affects approximately 1/150 maleThis condition affects approximately 1/150 male
infants, but only 1/750 female infants.infants, but only 1/750 female infants.

54. Annular PancreasAnnular Pancreas
The ventral and dorsal pancreatic budsThe ventral and dorsal pancreatic buds
form a ring around the duodenum, therebyform a ring around the duodenum, thereby
obstructing it.obstructing it.

55. OmphaloceleOmphalocele
The midgut fails to retract into theThe midgut fails to retract into the
abdominal cavity.abdominal cavity.
At birth, coils of intestine covered with only aAt birth, coils of intestine covered with only a
transparent sac of amniontransparent sac of amnion protrudeprotrude
from the umbilicus.from the umbilicus.

56. Malrotations of the MidgutMalrotations of the Midgut
The midgut does not rotate normally as itThe midgut does not rotate normally as it
retracts into the abdominal cavity.retracts into the abdominal cavity.
This usually presents as symptoms ofThis usually presents as symptoms of
intestinal obstruction shortly after birth.intestinal obstruction shortly after birth.
Malrotation also predisposes the infant to aMalrotation also predisposes the infant to a
volvulus of the midgutvolvulus of the midgut , wherein the, wherein the
intestines bind and twist around a shortintestines bind and twist around a short
mesentery.mesentery.
Volvulus usually interferes with the bloodVolvulus usually interferes with the blood
supply to a section of the intestines, and cansupply to a section of the intestines, and can
lead to necrosis and gangrene.lead to necrosis and gangrene.

57. Sub-hepatic Cecum andSub-hepatic Cecum and
AppendixAppendix
The cecum and appendix adhere to theThe cecum and appendix adhere to the
inferior surface of the liver during the fetalinferior surface of the liver during the fetal
period, andperiod, and
are carried upwards with it, resulting in anare carried upwards with it, resulting in an
abnormal anatomical position that mayabnormal anatomical position that may
create difficulties in diagnosingcreate difficulties in diagnosing
appendicitis.appendicitis.

58. Stenosis and Atresia of the Small IntestineStenosis and Atresia of the Small Intestine
Failure of recanalization of ileum during theFailure of recanalization of ileum during the
solid stage of development leads tosolid stage of development leads to
stenosis (narrowing) orstenosis (narrowing) or
atresia (complete obstruction) of theatresia (complete obstruction) of the
intestinal lumen.intestinal lumen.
Some stenoses and atresias may be causedSome stenoses and atresias may be caused
by an infarction of the fetal bowel owing toby an infarction of the fetal bowel owing to
impairment of its blood supply (cf. volvulus).impairment of its blood supply (cf. volvulus).

59. Congenital Aganglionic Megacolon (Hirschsprung’sCongenital Aganglionic Megacolon (Hirschsprung’s
disease)disease)
This results from the failure of neural crestThis results from the failure of neural crest
cells to migrate and form the myentericcells 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, andfecal retention, and
abdominal distention.abdominal distention.

60. Anorectal AgenesisAnorectal Agenesis
Abnormal formation of the urorectalAbnormal formation of the urorectal
septum causes the rectum to end as a blindseptum causes the rectum to end as a blind
sac above the puborectalis muscle.sac above the puborectalis muscle.

61. Anal AgenesisAnal Agenesis
Abnormal formation of the urorectalAbnormal formation of the urorectal
septum causes the rectum to end as a blindseptum causes the rectum to end as a blind
sac below the puborectalis muscle.sac below the puborectalis muscle.

62. Imperforate AnusImperforate Anus
The anal membrane fails to break downThe 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 ofwith severity depending on the thickness of
the intervening tissue.the intervening tissue.