Lecture 3 - GI Development

Question 1

When does the embryo fold

Answer 1

4th week

Question 2

Embryonic folding

Answer 2

Laterally

• creates ventral wall
• primitive gut becomes tubular

Craniocaudally

• creates cranial and caudal pockets from yolk sac endoderm
• beginning of primitive gut development

Question 3

Gut tube

Answer 3

Endoderm lined tube covered by splanchnic mesoderm
Runs the length of the body
Blind ended caudocephalically
Opening at the umbilicus

Question 4

Splanchnic mesoderm innervation and implication

Answer 4

Innervation by the visceral nervous system
- parasympathetic and sympathetic innervation

Therefore non localised pain

Question 5

Derivatives of the foregut

Answer 5

Oesophagus
Stomach
Pancreas, liver and gall bladder
Duodenum - proximal to the entrance of the bile duct (at sphincter of Oddi)

Question 6

Midgut derivatives

Answer 6

Duodenum 
Jejunum 
Ileum 
Caecum 
Ascending colon 
Proximal 2/3rds of the transverse colon

Question 7

Hind gut derivatives

Answer 7

Distal 1/3rd of transverse colon 
Descending colon 
Sigmoid colon
Rectum 
Upper anal canal
Internal lining of bladder and urethra

Question 8

Foregut blood supply

Answer 8

Coeliac trunk

Question 9

Midgut blood supply

Answer 9

Superior mesenteric artery

Question 10

Hindgut blood supply

Answer 10

Inferior mesenteric artery

Question 11

Duodenal blood supply

Answer 11

Proximal to sphincter of oddi:
Gastroduodenal artery and superior pancreaticoduodenal artery from the coeliac trunk

Distal to sphincter of Oddi:
Inferior pancreaticoduodenal artery from the superior mesenteric artery

Question 12

Pancreas blood supply

Answer 12

Superior and inferior pancreaticoduodenal artery from the coeliac trunk and superior mesenteric artery

Question 13

Intraembryonic coelom

Answer 13

One large cavity formed during embryonic folding

The diaphragm splits the coelom into abdominal and thoracic cavities

Question 14

Septum transversum

Answer 14

Indicates where the diaphragm will develop and separates the abdominal and thoracic cavities

Question 15

Mesentery

Answer 15

Double layer of peritoneum suspending the gut tube from the abdominal wall

• allows mobility
• allows a conduit for blood vessels and nerves

Question 16

What does the dorsal mesentery cover

Answer 16

Entire gut tube

Question 17

What does the ventral mesentery cover

Answer 17

Foregut

Question 18

Greater and lesser peritoneal sacs

Answer 18

In the foregut, the dorsal and ventral mesentery divides the cavity into left and right sacs

Left sac = greater sac
Right sac = lesser sac (behind stomach)

Question 19

Omenta

Answer 19

Specialised regions of peritoneum

Question 20

Greater omentum

Answer 20

Formed from the dorsal mesentery

Question 21

Lesser omentum

Answer 21

Formed from the ventral mesentery
Free edge is a conduit for the portal triad
Connects the liver and lesser curve of stomach

Question 22

Consequences of the rotation of the stomach

Answer 22

• Vague nerves move anterior and posterior to the stomach instead of left and right
• liver moves to the right of the stomach
• spleen moves to the left of the stomach
• shifts cardia and pylorus from the midline
• stomach lies obliquely
• formation of lesser sac and greater omentum

Question 23

Peritoneal reflection

Answer 23

Change in direction of peritoneum I.e.

• parietal to mesentery
• mesentery to visceral
• visceral to parietal

Question 24

Retroperitoneal

Answer 24

Never in the peritoneal cavity and never had a mesentery

Behind peritoneum

Question 25

Secondarily retroperitoneal

Answer 25

Began development invested in the peritoneal cavity and had a mesentery but during development, lost its mesentery as it fuses with the posterior abdominal wall E.g. duodenum and pancreas

Question 26

Where does the foregut extend from?

Answer 26

From the lung bud to the liver bud

Question 27

GI tract development

Answer 27

In the 4th week, a respiratory diverticula forms in the ventral wall of the foregut at the junction with the pharyngeal gut - respiratory primordial - ventral - oesophagus - dorsal

Question 28

Abnormal positioning of the tracheaoesophageal septum

Answer 28

- proximal blind ended oesophagus | - tracheoesophageal fistula

Question 29

Where does the liver and biliary system develop from

Answer 29

Ventral mesentery

Question 30

Where does the pancreas develop from?

Answer 30

Uncinate process and inferior head = ventral mesentery (duct system) Superior head, neck, body and tail = dorsal mesentery (gland portion)

Question 31

Falciform ligament

Answer 31

Connects the liver to the abdominal chest wall

Question 32

Duodenum development

Answer 32

Develops from the caudal foregut and cranial midgut Shape is due to stomach rotation as pushed to the right and against posterior abdominal wall Secondarily retroperitoneal

Question 33

What creates the greater curvature of the stomach

Answer 33

Faster growth of the dorsal border

Question 34

Where is the midgut connected to the yolk sac?

Answer 34

Midpoint of the midgut

Question 35

Physiological herniation

Answer 35

The midgut grows faster than the abdominal cavity so by week 6, it protrudes through the abs minimal wall into the umbilical cord

Question 36

Midgut rotation

Answer 36

Midgut rotates 90 degrees whilst in the umbilical cord In total the midgut rotates 3x of 90 degrees

Question 37

Umbilical hernia

Answer 37

If an abnormally large opening between the abdominal cavity and umbilical cord persists, an umbilical hernia can occur at birth