Devo

Question 1

What are the precursors of the GI tract?

Answer 1

Endoderm–epithelial components of gut
Splanchnic Mesoderm–muscle, connective tissue, and other layers of the wall of the gut
Coelomic epithelium covering the splanchnic mesoderm

Question 2

What does the foregut endoderm give rise to?

Answer 2

The epithelium of the esophagus, stomach, proximal duodenum, thyroid, lung, liver and pancreas

Question 3

What does the midgut endoderm give rise to?

Answer 3

The epithelium of the distal duodenum, jejunum, ileum, cecum, appendix and colon

Question 4

What does the hindgut endoderm give rise to?

Answer 4

The remaining part of the transverse colon, the descending and sigmoid colon, the rectum, and the superior part of the anal canal

Question 5

What does folding of the embryo in the transverse plane create?

Answer 5

The primitive gut tube from the endoderm

Question 6

What does folding of the embryo in the sagittal plane create?

Answer 6

Three subdivisions of the primitive gut tube – foregut, midgut and hindgut

Question 7

At about 7 weeks how does the 90 degree rotation change the position of the stomach?

Answer 7

The greater curvature (which arises from the embryonic dorsal side) now faces the left side of the body
The lesser curvature (which arose from the embryonic ventral side) faces the right side of the body

Question 8

What nerves innervated the anterior and posterior walls of the mature stomach?

Answer 8

Anterior wall – left vagus nerve

Posterior wall – right vagus nerve

Question 9

What is the space posterior to the stomach called?

Answer 9

The lesser sac or mental bursa

Question 10

What is the space anterior and inferior to the stomach called?

Answer 10

The greater sac

Question 11

Which ventral branch of the aorta is associated with the foregut, midgut and hindgut respectively?

Answer 11

Foregut: celiac trunk
Midgut: superior mesenteric
Hindgut: inferior mesenteric

Question 12

Describe the physiological umbilical herniation.

Answer 12

Forms by week 6 when midgut loop herniates through the umbilicus into the umbilical cord

Question 13

What do the midgut loop cranial and caudal limbs become??

Answer 13

The cranial limb forms the primordial jejunum and ileum

The caudal limb develops the cecal bud which ultimately forms the cecum

Question 14

When is the body cavity large enough for the midgut to retract into it?

Answer 14

Around week 10

Question 15

After retraction into the body cavity, where are the cranial limb and caudal limbs localized?

Answer 15

Cranial limb on the left side of the body

Caudal limb on the right side of the body

Question 16

What is the cloaca?

Answer 16

The expanded terminal region of the hindgut
The dorsal side produces the rectum and part of the anal canal
The ventral side produces the urogenital sinus

Question 17

What develops into the anal canal?

Answer 17

The superior part develops form the handgun

The inferior region develops from the proctodeum (ectodermally-derived)

Question 18

What gives rise to the liver, gallbladder and biliary duct system?

Answer 18

The outgrowth of the ventral foregut endoderm

Question 19

What are the three distinct phases of liver bud formation?

Answer 19

1. Foregut endoderm composed of polarized columnar epithelial cells protrudes into the surrounding septum transversum mesenchyme
2. The simple columnar epithelium transforms to a pseudostratified epithelium encased in basement membrane.
3. The basement membrane is degraded and bipotential hepatoblasts delaminate and migrate into the septum transverse mesenchyme – have the potential to differentiate into hepatocytes, epithelial cells of the liver parenchyma or into cholangiocytes (epithelial cells of the biliary system)

Question 20

What growth factors help the primordial liver bud along its development?

Answer 20

FGFs and BMPs secreted from heart and the septum transversum mesenchyme

Question 21

What is the key site of hematopoiesis in the fetus?

Answer 21

The liver!!

Question 22

What gives rise to the gallbladder?

Answer 22

A small caudal region of the liver bud

The stalk of the bud forms the cystic duct

Question 23

What gives rise to the bile duct?

Answer 23

The stalk connecting the hepatic and cystic ducts to the duodenum

Question 24

How does the pancreas develop?

Answer 24

As two buds emanating from the oral and ventral foregut endoderm – The dorsal pancreatic bud and the ventral pancreatic bud

Question 25

What growth factors are involved in the development of the dorsal pancreatic bud?

Answer 25

The notochord secretes FGF2 and activin to inhibit the growth factor sonic hedgehog and promote pancreatic development instead of intestinal development

Question 26

Duodenal atresia or duodenal stenosis

Answer 26

Failure to reanalyze or incomplete recanalization of the duodenum –> leads to vomiting
Polyhydramnios occurs with duodenal atresia b/c the blockage prevents proper intestinal absorption of swallowed amniotic fluid

Question 27

Extrahepatic biliary atresia

Answer 27

Serious anomaly
Commonly caused by obliteration of the bile ducts (85%)
Jaundice soon after birth and stools are echoic (clay colored)
Fatal without liver transplant

Question 28

Gastroschisis

Answer 28

Defect lateral to the medial plane of the anterior abdominal wall
Abdominal viscera is extruded through eh wall without involving the umbilical cord
Usually occurs on the right side lateral to the umbilicus
Is NOT a hernia because it is not covered in a sac – it is an evisceration

Question 29

Omphalocele

Answer 29

Herniation of abdominal contents into the proximal umbilicus
Failure of intestine to return to the abdomen during development causes omphalocele

Question 30

Why do congenital anomalies of the small intestine commonly occur?

Answer 30

Because of defects in gut rotation including nonrotation or malrotation

Question 31

Meckel divertitculum

Answer 31

Out pocketing of ileum, common anomaly of GI tract – remnant of the omphaloenteric duct
Can become inflammed and mimic appendicitis

Question 32

Hirschsprung disease

Answer 32

Aganglionosis of the colon – presents as megacolon because the affected tissue (which lacks ganglion cells) fails to relax –> prevents movement of bowel contents