GI Development - Bolender Flashcards
When does the region of the gut tube destined to become the stomach begin to dilate?
~Week 4
Describe the development of the greater and lesser curvatures of the stomach
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.
When does the stomach rotate so that the greater and lesser curvatures are in their final right-left orientation?
~Week 7
Rotation of the stomach produces a space immediately behind the stomach. Name it.
Lesser sac (omental bursa)
Extension of which mesentery gives rise to the greater omentum?
dorsal mesentery
Describe the type of epithelium lining the stomach
Which embryologic tissue is its precursor?
simple columnar
foregut endoderm
What is the embryonic precursor tissue of the smooth muscle and connective tissue of the stomach?
splanchnic mesenchyme
Approximately where is the anatomic boundary between the foregut and the midgut?
between parts 2 & 3 of the duodenum, distal to the bile duct
With respect to the GI tract, what is formed during transverse folding of the embryo?
Saggital folding?
primitive gut tube
three subdivisions of the primitive gut tube: foregut, midgut, hindgut
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?
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
Around week 6, what happens to the midgut?
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.
When does the developing midgut retract back into the body? Describe the process.
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.
What marks the transition from midgut-derived colon to hindgut-derived colon
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
Name the branch of the abdominal aorta that chiefly supplies each of the following:
- foregut
- midgut
- hindgut
Celiac trunk
SMA
IMA
When does partitioning of the cloaca complete?
~Week 7
What are hepatic sinusoids?
Blood vessels residing at the basal surface of hepatocytes
Describe the three phases of formation of the liver bud (hepatic diverticulum)
- 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.
- The simple columnar epithelium transforms to a pseudostratified epithelium encased in basementmembrane.
- 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.
The uncinate process of the pancreas is derived from what?
The ventral pancreatic bud of the foregut. The rest of the pancreas develops from the dorsal bud
Failure or partial failure to re-canalize the duodenum during development can lead to what?
Duodenal atresia (complete occlusion) or
Duodenal stenosis (partial occlusion)
Describe development of polyhydramnios with duodenal atresia?
Vomiting due to duodenal atresia will contain what?
Polyhydramnios - excess amniotic fluid - occurs due to blockage preventing intensinal absorption of swallowed amniotic fluid
Vomit will contain bile
Is gastroschisis a hernia?
Describe it.
Where does it occur?
Name one major consequence
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
What is an omphalocele?
Herniation of the abdominal viscera into the proximal umbilicus. May also include liver, stomach, and gonads
Mispositioning of the intestine (due to abnormal of deficienct rotation) can lead to what?
volvulus -> obstruction, infarction, tissue death
Outpocketing of the iluem as a result of a persistent vitelline duct is called what?
Meckel’s diverticulum
May also present as a cyst or fistula
Describe Hirschsprung Disease
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.
Describe the clinical presentation of extrahepatic biliary atresia
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)
