GI Development - Bolender

Question 1

When does the region of the gut tube destined to become the stomach begin to dilate?

Answer 1

~Week 4

Question 2

Describe the development of the greater and lesser curvatures of the stomach

Answer 2

The dorsal wall of the developing stomach expands more quickly than the ventral wall. The dorsal wall becomes the greater curvature and the ventral wall becomes the lesser curvature. The stomach then rotates 90 degrees clockwise around its longitudonal axis to that the greater and lesser curvatures are on the left and right side respectively.

Question 3

When does the stomach rotate so that the greater and lesser curvatures are in their final right-left orientation?

Answer 3

~Week 7

Question 4

Rotation of the stomach produces a space immediately behind the stomach. Name it.

Answer 4

Lesser sac (omental bursa)

Question 5

Extension of which mesentery gives rise to the greater omentum?

Answer 5

dorsal mesentery

Question 6

Describe the type of epithelium lining the stomach

Which embryologic tissue is its precursor?

Answer 6

simple columnar

foregut endoderm

Question 7

What is the embryonic precursor tissue of the smooth muscle and connective tissue of the stomach?

Answer 7

splanchnic mesenchyme

Question 8

Approximately where is the anatomic boundary between the foregut and the midgut?

Answer 8

between parts 2 & 3 of the duodenum, distal to the bile duct

Question 9

With respect to the GI tract, what is formed during transverse folding of the embryo?

Saggital folding?

Answer 9

primitive gut tube

three subdivisions of the primitive gut tube: foregut, midgut, hindgut

Question 10

During development, what structure is found at the junction between the cranial and caudal portions of the midgut?

The cranial portion gives rise to what?

The caudal portion gives rise to what?

Answer 10

The vitelline/omphalomesenteric duct/yolk stalk

most of the small intestine - distal duodenum, jejunum, most of the ileum

distal ileum, cecum, appendix, ascending colon, proximal 2/3 of transverse colon

Question 11

Around week 6, what happens to the midgut?

Answer 11

The midgut grows more quickly than the body cavity can expand, causing it to herniate through the umbilicus.

The midgut then rotates 90 degrees, resulting in the cranial portion right and the caudal portion on the left. Continued growth of the cranial limb forms loops of small bowel. The caudal limb develops the cecal bud.

Question 12

When does the developing midgut retract back into the body? Describe the process.

Answer 12

Week 10

The body cavity has grown sufficiently to accomodate the midgut. The midgut rotates a further 180 degrees counterclockwise, bringing the primitive transverse colon into position in front of the duodenum. The ascending colon elongates, lowering the cecum into its final caudal position on the right side.

Question 13

What marks the transition from midgut-derived colon to hindgut-derived colon

Answer 13

Blood supply (though yes, it is all anastomosed via the marginal arteries)

Midgut (promixal 2/3 of transverse colon): SMA

Hindgut (distal 1/3 of transverse colon): IMA

Question 14

Name the branch of the abdominal aorta that chiefly supplies each of the following:

• foregut
• midgut
• hindgut

Answer 14

Celiac trunk

SMA

IMA

Question 15

When does partitioning of the cloaca complete?

Answer 15

~Week 7

Question 16

What are hepatic sinusoids?

Answer 16

Blood vessels residing at the basal surface of hepatocytes

Question 17

Describe the three phases of formation of the liver bud (hepatic diverticulum)

Answer 17

1. The foregut endoderm composed of polarized columnar epithelial cells rotrudes into the surrounding septum transversum mesenchyme. The septum transversum mesenchyme derives from the splanchnic mesoderm between the heart and the midgut. The apical surface faces the gut lumen and the basal surfaces contact laminin-rich basement membrane.
2. The simple columnar epithelium transforms to a pseudostratified epithelium encased in basementmembrane.
3. The basement membrane is degraded, and bipotential hepatoblasts delaminate and migrate into the septum transversum mesenchyme forming cords of hepatic cells within the mesenchyme. The hepatoblasts have the potential to differentiate into hepatocytes, the epithelial cells of the liver parenchyma, or into cholangiocytes, the epithelial cells of the biliary system.

Question 18

The uncinate process of the pancreas is derived from what?

Answer 18

The ventral pancreatic bud of the foregut. The rest of the pancreas develops from the dorsal bud

Question 19

Failure or partial failure to re-canalize the duodenum during development can lead to what?

Answer 19

Duodenal atresia (complete occlusion) or

Duodenal stenosis (partial occlusion)

Question 20

Describe development of polyhydramnios with duodenal atresia?

Vomiting due to duodenal atresia will contain what?

Answer 20

Polyhydramnios - excess amniotic fluid - occurs due to blockage preventing intensinal absorption of swallowed amniotic fluid

Vomit will contain bile

Question 21

Is gastroschisis a hernia?

Describe it.

Where does it occur?

Name one major consequence

Answer 21

No, not a hernia

Results from a defect in the anterior abdominal wall. The abdominal viscera protrudes through the abdominal wall.

Usually on the right side lateral to the umbilicus

Serositis - due to exposure of the viscera to amniotic fluid

Question 22

What is an omphalocele?

Answer 22

Herniation of the abdominal viscera into the proximal umbilicus. May also include liver, stomach, and gonads

Question 23

Mispositioning of the intestine (due to abnormal of deficienct rotation) can lead to what?

Answer 23

volvulus -> obstruction, infarction, tissue death

Question 24

Outpocketing of the iluem as a result of a persistent vitelline duct is called what?

Answer 24

Meckel’s diverticulum

May also present as a cyst or fistula

Question 25

Describe Hirschsprung Disease

Answer 25

Aganglionosis of the colon

Presents as megacolon -> dilation occurs because tissue distal to the dilation lacks ganglion cells, and therefore fails to relax. The tissue in the dilation itself is normal.

Question 26

Describe the clinical presentation of extrahepatic biliary atresia

Answer 26

Biliary tree defect leading to bile duct obstruction and damage to the liver

Jaundice soon after birth with acholic (clay-colored) stools (stools lack bile)

Fatal if untreated (surgical or liver transplant)