7. Embryology

Question 1

What happens from day 30-35?

Answer 1

• Gut tube starts to develop
• Formed from 2 layers of germline tissue
- endoderm
- mesoderm
• Submucosal and myenteric plexus arise separately from the neural crest

Question 2

What is the endoderm and mesoderm?

Answer 2

• Endoderm
- forms the inner layer
- has cells => develops into mucosal epithelium, mucosal and submucosal glands
• Mesoderm
- wrapped around the endoderm to provide structural and functional support
- cells become the lamina propria, gut smooth muscle, blood vessels and serosa

Question 3

What happens from day 35-39?

Answer 3

• Duodenum and stomach become more separated
• Pancreas starts to develop from 2 sites
• Ventral pancreatic bud (larger) spouts from liver bud
• Dorsal pancreatic bud (smaller) spouts from duodenum

Question 4

What happens from day 40-55?

Answer 4

• Pancreas continues to develop
• Endoderm develops into branched tubules - later become ducts attached to secretory acini
• Endocrine pancreas arise from stem cells at duct branch points
- disconnect from ducts => discrete islands of vascularised endocrine tissue
• Primary rotation of gut tube - ventral pancreas and biliary system swing to dorsal pancreas
• Creates C-shaped duodenum

Question 5

What happens at day 56?

Answer 5

• Pancreas portions fuse
• Ventral pancreas (now smaller) => uncinated process
• Ventral pancreatic duct connects to biliary tree via common vile duct
- gall bladder via cystic duct
- liver via hepatic duct
• Dorsal duct fuses with common bile duct