Development of GIT (Foregut Structures)

Question 1

What is the primordium of the gut tube?

Answer 1

The secondary yolk sac becomes enclosed within the embryo during folding, forming the primordium of the gut tube (foregut, midgut, hindgut).

Question 2

What are the three main divisions of the gut tube?

Answer 2

Foregut: Esophagus, stomach, liver, gallbladder, pancreas.

Midgut: Small intestine (except duodenum proximal to bile duct), cecum, ascending colon, proximal 2/3 of transverse colon.

Hindgut: Distal 1/3 transverse colon, descending colon, rectum, upper anal canal.

Question 3

How does the esophagus form?

Answer 3

A tracheoesophageal septum divides the foregut into the anterior laryngotracheal tube and posterior esophagus. Rapid elongation occurs as the heart and diaphragm descend.

Question 4

What causes tracheoesophageal fistulas (TOFs)?

Answer 4

Incomplete formation of the tracheoesophageal septum, leading to abnormal connections between the esophagus and trachea.

Question 5

Describe the initial appearance and rotation of the stomach.

Answer 5

Fusiform dilation of the foregut at week 4. Rotates 90° clockwise along its longitudinal axis, making the right side posterior and left side anterior.

Question 6

How does the vagus nerve innervation relate to stomach rotation?

Answer 6

Left vagus nerve innervates the anterior wall; right vagus nerve innervates the posterior wall due to rotation.

Question 7

How do the liver and gallbladder develop?

Answer 7

Hepatic bud arises from the ventral foregut, grows into septum transversum, and bifurcates into liver lobes. Cystic bud forms the gallbladder and cystic duct.

Question 8

What are the consequences of stomach rotation on mesenteries?

Answer 8

Dorsal mesogastrium forms the greater omentum and omental bursa (lesser sac). Ventral mesogastrium forms the lesser omentum and falciform ligament.

Question 9

Describe pancreatic development.

Answer 9

Dorsal pancreatic bud: Forms upper head, body, and tail.

Ventral pancreatic bud: Forms uncinate process and lower head. Fusion of buds creates the main pancreatic duct.

Question 10

What is the relationship of the pancreas to the SMA?

Answer 10

SMA passes posterior to the pancreatic body but anterior to the uncinate process.

Question 11

What are the derivatives of the ventral and dorsal mesogastria?

Answer 11

Ventral mesogastrium: Lesser omentum (hepatoduodenal/ hepatogastric ligaments) and falciform ligament.

Dorsal mesogastrium: Greater omentum, gastrosplenic ligament, splenorenal ligament.

Question 12

Which arteries supply the foregut, midgut, and hindgut?

Answer 12

Foregut: Celiac artery.

Midgut: Superior mesenteric artery.

Hindgut: Inferior mesenteric artery.

Question 13

What is annular pancreas?

Answer 13

Ventral pancreatic bud encircles the duodenum due to abnormal migration, causing obstruction.

Question 14

When does the gut tube begin to form?

Answer 14

Week 4: Embryo folds (cranially, caudally, laterally), incorporating the yolk sac as the gut primordium.

Question 14

When does the stomach appear?

Answer 14

Week 4: Fusiform dilation of the foregut caudal to the esophagus.

Question 15

What marks the boundaries of the foregut and hindgut?

Answer 15

Foregut: Buccopharyngeal membrane (anterior limit).

Hindgut: Cloacal membrane (posterior limit).

Question 16

What structures form from the ventral mesentery?

Answer 16

Lesser omentum (hepatoduodenal/hepatogastric ligaments) and falciform ligament.

Question 17

How is the omental bursa (lesser sac) formed?

Answer 17

Rotation of the stomach causes the dorsal mesogastrium to fold, creating a space posterior to the stomach.

Question 18

What is the epiploic foramen?

Answer 18

Entrance to the omental bursa; bordered by the portal triad (hepatic artery, bile duct, portal vein) in the hepatoduodenal ligament.

Question 19

How does the spleen develop?

Answer 19

Forms within the dorsal mesogastrium, splitting it into:

Gastrosplenic ligament (stomach to spleen).

Splenorenal ligament (spleen to kidney).

Question 20

What is the vitelline duct?

Answer 20

Narrow remnant of the yolk sac connecting the midgut to the yolk sac. Persistence leads to Meckel’s diverticulum.

Question 21

How does the liver’s blood supply develop?

Answer 21

Sinusoids form from vitelline and right umbilical veins; connective tissue derives from the septum transversum.

Question 22

What structures form from the ventral and dorsal pancreatic buds?

Answer 22

Ventral bud: Uncinate process and lower head.

Dorsal bud: Upper head, body, tail.

Question 23

What is the main pancreatic duct?

Answer 23

Fusion of the ventral bud duct (with common bile duct) and distal dorsal bud duct.

Question 24

What is the accessory pancreatic duct (of Santorini)?

Answer 24

Persistence of the proximal dorsal bud duct; drains into the minor duodenal papilla.

Question 25

What causes esophageal atresia/stenosis?

Answer 25

Incomplete recanalization of the esophageal lumen or defective tracheoesophageal septum.

Question 26

What is annular pancreas?

Answer 26

Ventral pancreatic bud encircles the duodenum → obstruction

Question 27

How does biliary atresia occur?

Answer 27

Failure of bile duct recanalization → blocked bile flow.

Question 28

What is intestinal malrotation?

Answer 28

Incomplete rotation of the midgut around the SMA → volvulus risk.

Question 29

Which arteries supply the foregut, midgut, and hindgut?

Answer 29

Foregut: Celiac trunk. Midgut: Superior mesenteric artery (SMA). Hindgut: Inferior mesenteric artery (IMA).

Question 30

Why does the left vagus nerve innervate the anterior stomach?

Answer 30

Stomach rotation shifts the original left side anteriorly.

Question 30

Label the foregut derivatives:

Answer 30

Esophagus, stomach, liver, gallbladder, pancreas, proximal duodenum.

Question 30

Trace the path of the ventral and dorsal pancreatic buds.

Answer 30

Ventral bud migrates dorsally to fuse with the dorsal bud.

Question 31

What is the significance of the septum transversum?

Answer 31

Gives rise to the central tendon of the diaphragm and ventral mesentery.

Question 32

When does the yolk sac fully regress?

Answer 32

By week 10, leaving the vitelline duct (if persistent → Meckel’s).

Question 33

What is the role of splanchnic mesoderm?

Answer 33

Forms smooth muscle/connective tissue of the gut wall.