Embryology of the GI Tract

Question 1

At what point during embryonic development does the primordial gut tube form?

Answer 1

The 4th week

Question 2

What is the primordial gut derived from?

Answer 2

The endoderm lining the yolk sac

Question 3

What seals the primordial gut tube?

Answer 3

Cranial End - Oropharyngeal Membrane

Caudal End - Cloacal Membrane

Question 4

What is the oesophagus derived from?

Answer 4

The cranial part of the primitive gut tube

Question 5

What is the trachea-oesophageal septum?

Answer 5

The ridge that divides the foregut tube into the trachea and oesophagus

Question 6

What happens if the trachea-oesophageal septum deviates incorrectly?

Answer 6

There is incomplete separation of the laryngo-tracheal tube which results in oesophageal atresia and trachea-oesophageal fistula

Question 7

What structure is the stomach formed from?

Answer 7

The foregut

Question 8

How does the stomach grow differentially to the size and location it has in an adult?

Answer 8

1. Differential growth creates the greater and lesser curves
2. The stomach rotates 90 degrees around its longitudinal axis
3. The stomach undergoes an anterio-posterior rotation to create the final adult position

Question 9

How is the lesser sac created?

Answer 9

It is created when the stomach rotates, pulling the dorsal mesentery to the left and creating the lesser sac

Question 10

What structures form the duodenum?

Answer 10

The caudal part of the foregut and cranial part of the midgut

Question 11

What is the blood supply to the duodenum?

Answer 11

Coeliac Trunk and Superior Mesenteric Artery

Question 12

At what point in embryonic development does the liver first appear?

Answer 12

The liver primordium bud appears in the middle of the 3rd week

Question 13

Where does the liver bud grow?

Answer 13

Into the septum transversum plate between the pericardial cavity and yolk sac

Question 14

What structure forms the bile duct?

Answer 14

The connection between the liver and foregut narrows to form the bile duct

Question 15

From what structure are the gall bladder and cystic duct formed?

Answer 15

The ventral outgrowth from the bile duct

Question 16

At what point during development is the spleen formed/

Answer 16

5th week

Question 17

From what structure is the spleen derived from?

Answer 17

Mesoderm

Question 18

At what point during development does the spleen start its lymphoid function?

Answer 18

Week 23

Question 19

What is the pancreas formed from?

Answer 19

From 2 buds which grow from the endodermal lining of the duodenum in week 5

Question 20

What structures fuse to form the main pancreatic duct?

Answer 20

Ventral Duct + Distal Part of Dorsal Duct

Question 21

What structure can the proximal part of the dorsal duct form?

Answer 21

The accessory duct

Question 22

What cause an annular pancreas?

Answer 22

The ventral bud failing to migrate around the duodenum correctly

Question 23

What are the consequences of an annular pancreas?

Answer 23

It may cause duodenal stenosis and accessory pancreatic tissue

Question 24

What structures will be formed from the cephalic end of the primary intestinal loop?

Answer 24

Distal duodenum, jejunum and proximal ileum

Question 25

What structures will be formed from the caudal end of the primary intestinal loop?

Answer 25

The distal ileum, caecum, appendix, ascending colon and the proximal 2/3 of the transverse colon

Question 26

How and when does the midgut rotate?

Answer 26

The primary intestinal loop rotates 90 degrees anti-clockwise around the axis of the superior mesenteric artery in the 6th week of development

Question 27

What is physiological herniation of the midgut?

Answer 27

When the gut tube herniates into the extraembryonic cavity in the umbilical cord to make room for the gut tube to grow

Question 28

At what point do the herniated loops retract?

Answer 28

During the 10th week when there is more space in the abdominal cavity

Question 29

What is omphalocele?

Answer 29

Herniation of abdominal viscera through an enlarged umbilical ring and failed retraction of the umbilical ring

Question 30

What is gastrochisis?

Answer 30

Herniation of abdominal contents directly through the body wall into the amniotic cavity. The contents are not covered by peritoneum or amnion and they herniate through a week spot to the right of the umbilicus

Question 31

What consequences can arise from remnants of the vitelline duct?

Answer 31

It forms Meckel's diverticulum and may form fistula or vitelline cyst/ligament

Question 32

What structures make up the hindgut?

Answer 32

Distal 1/3 transverse colon, descending colon, sigmoid colon, rectum and anal canal

Question 33

What structures does the endoderm of the hindgut form?

Answer 33

The lining of the bladder and urethra

Question 34

What is the cloaca?

Answer 34

The endoderm lined cavity with surface ectoderm at its ventral border

Question 35

At what point in development does the cloacal membrane rupture opening the hindgut?

Answer 35

End of week 7