Embryology 1

Question 1

Following gastrulation, what do each of the 3 layers of the trilaminar embryo contribute to in the GI system?

Answer 1

Endoderm: mucosa from pharynx to upper 2/3 of anal canal. All organ epithelium
is formed by evaginations from the gut tube (submandibular/sublingual glands; liver; pancreas; gall bladder).

Mesoderm: connective tissue and smooth muscle.

Ectoderm: mucosa at ends of tube (mouth, parotid; lower 1/3 of anal canal) and enteric ganglia (from neural
crest cells).

Question 2

What defect results from persistence of the vitelline duct?

Answer 2

Meckel Diverticulum

Question 3

What embryologic defect is associated with the “rule of 2s”? Describe the rule of 2s.

Answer 3

Meckel Diverticulum

RULE OF 2’s: affects 2% of population; found 2 feet from iliocecal valve; typically
about 2 inches long; contains 2 types of ectopic tissue (stomach and pancreas);
age of presentation is typically 2 years of age; males are 2X more likely to be
affected

Question 4

Describe Hirschprung Disease?

Answer 4

(congenital megacolon): failure of migration of neural crest cells to
the caudal 1/3 of large intestine. Causes lack of muscular contractions, resulting in inability
to properly clear feces. Radiologically, shows lack of haustra.

Question 5

Where does the lung bud develop from in the gut tube?

Answer 5

Respiratory diverticulum develops as a pouch from the foregut.

Question 6

Which portion of the stomach grows fastest in the stomach?

Answer 6

Greater curvature (dorsal aspect.

Question 7

What is the significance of the blood supply to the duodenum as derived from embryologic development?

Answer 7

parts 1 and 2 are derived from the foregut; 3, 4 from midgut. This produces an anastomosis due to
two blood supplies (celiac; SMA).

Question 8

Describe a key time in duodenal development. Describe a birth defect that can result from a mistake during this period?

Answer 8

Lumen: obliterated (filled in) during the 2nd month. Later recanalized by apoptosis.

Duodenal Stenosis (narrowing) or Atresia (complete blockage)
can result if the recanalization does not complete
successfully.

Question 9

Describe the signs and symptoms of duodenal atresia.

What will often be seen on radiographic imaging

Answer 9

Blockage of the duodenum leads to
vomiting (if bilious, the blockage is distal to the main pancreatic duct).
Radiograph will have “double bubble sign”, air will fill the stomach and
proximal duodenum with a compressed area at the pyloric sphincter.

Question 10

Describe the development of the pancreas.

Answer 10

Begins as two outgrowths of duodenum (dorsal, ventral).

• Dorsal bud: most of pancreas comes from this bud.
• Main pancreatic duct: proximal portion from ventral bud, distal portion from
  dorsal bud.
• Accessory duct: completely from dorsal bud. Superior to main pancreatic duct. Not present in all
  individuals.

Question 11

Describe the common birth defects associated with the development of the foregut.

Answer 11

VACTERL and VATER. Commonly occur with use of progesterone-estrogen contraceptives during critical period
of gestation.

Vertebral: spina bifida.
Anal.
Cardiac: Tetralogy of Fallot.
Tracheal.
Esophageal.
Renal: horseshoe kidney.
Limbs: poly/syndactyly.

Respiratory system: duplications, diverticula, cysts, atresia, stenosis,
fistulas.

Tracheoesophageal fistula: most common. Esophagus ends in blind pouch, distal portion of GI system is connected to
trachea.

Duodenum: atresia (total blockage; A, B). Stenosis
(narrowing; C, D).
Pancreas: variations in ducts and blood supply are numerous.

Annular pancreas: ventral and dorsal buds do not properly rotate causing the pancreas to surround and
compress the duodenum (stenosis). Can also cause double bubble.

Question 12

During week six, what happens as the midgut develops and becomes too large for the midgut cavity?

Answer 12

Physiological herniation of SMA supplied contents surrounded in amnion. It herniates, rotates around the SMA axis and re-enters around week 10

Question 13

Indicate and describe the common birth defects related to the development of the midgut. (Vitelline Duct)

Answer 13

Meckel diverticulum: portion of duct attached to intestine persists. Usually connected to
umbilicus by fibrous cord.

Vitelline fistula: persistence of vitelline duct. Allows communication between intestines and
outside of the body via umbilicus.

Vitelline cyst: fluid filled cavity that persists. Usually connected to umbilicus and intestine by
fibrous cords.

Question 14

Indicate and describe the common birth defects related to the development of the midgut. (Gastrochisis)

Answer 14

ventral body wall defect results in the gut contents outside the
body. (no amnion)

Question 15

Indicate and describe the common birth defects related to the development of the midgut. (Omphalocele)

Answer 15

herniation of gut into umbilical cord. Covered by amnion.

Question 16

Indicate and describe the common birth defects related to the development of the midgut (Umbilical Hernia)

Answer 16

herniation of gut out region of umbilicus. Covered by skin.

Question 17

Indicate and describe the common birth defects related to the development of the midgut. (Malposition/Malrotations)

Answer 17

Can include non-rotation; situs inversus; wrong rotation (small
intestines ventral to transverse colon).

Volvulus: strangulation of intestine due to rotation (twisting) of mobile portions
about itself. This can lead to blockage or necrosis (strangulation of blood supply).

Question 18

What division is marked by the pectinate line?

Answer 18

marks division point between extoderm and endoderm. This division is also the
transition point for blood supply, innervation and lymphatic drainage (visceral to somatic).

Question 19

Describe Hirschprung Disease?

Answer 19

failure of neural crest cells to migrate to caudual 1/3 of large intestine. This
results in absence of enteric ganglia (Auerbach and Meissner plexi).

Question 20

Describe the development of the hindgut portion known as the urorectal septum

Answer 20

forms from two folds
(Tournoux and Rathke)
that divide cloaca into
UG sinus (bladder,
urethra) and recto-anal
canal.

Question 21

Describe the development of the anal canal?

Answer 21

2/3 from hindgut, lower 1/3 from surface ectoderm (anal pit = proctoduem).
Pectinate line: marks division point between extoderm and endoderm. This division is also the
transition point for blood supply, innervation and lymphatic drainage (visceral to somatic).

Question 22

Describe the development of the cloaca.

Answer 22

endoderm lined cavity in contact with surface ectoderm. Continuous with hindgut. Cloacal membrane is
the region of contact between the two.

Question 23

Describe fistulas with regard to the hindgut.

Answer 23

imporper formation of urorectal septum. Can be a result of improper alignment of Tourneux
and Rathke folds.

Question 24

What is an imperforate anus?

Answer 24

failure of anorectal canal to form (recto- fistula).

Question 25

What’s the difference between a vitelline fistula and a urachal fistula

Answer 25

Both leak some body fluid from the umbilicus

Urachal fistula is from bladder

Vitalline fistual is from Small intestine