3 Development of the Gastrointestinal tract

Question 1

How is the primitive gut tube created?

Answer 1

Embryonic folding- 4th week

Lateral folding

Ventral body wall

Primitive gut= tubular

Craniocaudal folding

Creates cranial and caudal pockets

Question 2

What is the gut tube?

Answer 2

Endoderm lined tube

Runs length of body

Has blind pouches at head and tail ends

Opening at umbilicus

Splanchinic mesoderm covering

(development begins week 3)

Question 3

Label the parts of the primitive gut tube:

Answer 3

Question 4

List the derivatives of the foregut, midgut and hindgut respectively. (remember where they divide)

Answer 4

Divisions:

Foregut-Midgut= bile duct entrance in duodenum

Midgut- Hindgut= 2/3 along transverse colon

Question 5

Each embryonic gut receives blood supply from a distinct branch of the abdominal aorta. What are these branches?

Answer 5

Question 6

Why do the duodenum and the pancreas have mixed blood supplies? Describe the blood supply to the duodenum

Answer 6

Structures develop close to junction between foregut and midgut

• Duodenum
  
  • Celiac trunk
    
    • Gastroduodenal artery
    • Superior pancreaticoduodenal
  • Superior mesenteric
    
    • Inferior pancreaticoduodenal
      *

Question 7

Describe the blood supply to the pancreas

Answer 7

Pancreas (head)

Celiac

Superior pancreaticoduodenal

Superior mesenteric

Inferior pancreaticoduodenal

Question 8

What is the internal lining of the gut tube derived from and what does it eventually become?

Answer 8

Derived from: Endoderm

Becomes: Epithelia

Question 9

What is the external lining of the primitive gut tube made from and what does it eventually become?

Answer 9

Derived from: Splanchnic mesoderm

Becomes: Future musculature and peritoneum

Question 10

What are the 2 layers that the mesoderm split into?

Answer 10

1. Somatic (abdominal wall)
2. Splanchnic (smooth muscles of gut wall and peritoneum)

Question 11

The space created by the splitting of the 2 mesoderm layers is the coelomic cavity. What does the coelomic cavity eventually become?

Answer 11

Pleural cavity

Peritoneal cavity

Question 12

What are mesenteries and what is their function?

Answer 12

Double layer of peritoneum- suspending gut tube from abdominal wall

Function:

Allow passage of blood and nerve supply

Allow mobility when needed

Question 13

All 3 regions of the embryonic gut tube are suspended from the dorsal body wall by the dorsal mesenteries. Which region is the only region with a ventral mesentery?

Answer 13

Foregut

Ventral mesentery attaches foregut to floor of abdominal cavity

Question 14

What are omenta? (general terms)

Answer 14

Specialised regions of peritoneum

Question 15

Where are the greater and lesser omenta formed from?

Answer 15

• Greater: dorsal mesentery
• Lesser: ventral mesentery

Question 16

What does the free edge of the lesser omentum facilitate the conduction of?

Answer 16

Portal triad

Question 17

Give examples of 2 parts of the GI tract that remain suspended from the posterior abdominal wall by a mesentery and remain mobile.

Answer 17

Jejunum

Ileum

Question 18

What does it mean to be:

• Retroperitoneal
• Secondarily retroperitoneal

Answer 18

• Retroperitoneal
  
  • Structure not suspended in abdominal cavity
  • Were never in peritoneal cavity and never had a mesentery
• Secondarily retroperitoneal
• eg pancreas and duodenum
  
  • Began development invested in peritoneum
  • Had mesentery
  • Eventually mesentary lost through fusion of posterior abdominal wall

Question 19

How does the gut become open to the exterior at the future mouth and anus?

Answer 19

Forgut- blind end: Oropharyngeal membrane

Hindgut- blind end: Cloacal membrane

Membranes break down- gut opens to exterior

Question 20

What does the rotation of the stomach result in the formation of?

Answer 20

Rotation of stomach- results in formation of greater and lesser sacs

Question 21

How does the separation of the GI and Respiratory tracts occur in the developing embryo?

Answer 21

Formation of respiratory diverticulum

In ventral wall of foregut

4th week

(Can go wrong- cause variety of abnormalities)

Question 22

How does the stomach acquire its characteristic shape (greater curve) and position?

Answer 22

SHAPE: Dorsal border develops faster than ventral

POSITION: Week 4, slight dilation of distal foregut

Question 23

Where do the liver and the biliary system develop from?

Answer 23

Ventral mesentery

Question 24

Where does the pancreas develop from? (different parts- different places)

Answer 24

• Ventral mesentery
  
  • Uncinate process
  • Inferior head
• Dorsal mesentery
  
  • Superior head
  • Neck
  • Body
  • Tail

Question 25

How does the duodenum become secondarily retroperitoneal?

Answer 25

Rotation of stomach- pushes duodenum right, then against posterior abdominal wall

Question 26

The lumen of the duodenum is obliterated in the 5th and 6th weeks of development. When is it recanalised?

Answer 26

End of embryonic period

Question 27

How many layers of peritoneum make up the omenta?

Answer 27

4 layers