embryology

Question 1

gut tube formation occurs when and how?

Answer 1

• the lateral edges of the endoderm fold together and fuse forming the gut tube, visceral mesoderm will also form and externally layer the gut tube
• formed during embryonic folding

Question 2

origins of the GI tract

Answer 2

there are 3 main cell types:

• endoderm > mucosal epithelium, things that line the gut ( eg liver, pancreas)
• visceral mesoderm > connective tissue structures, smooth muscle components (lamina propria etc)
• neural crest > ENS

in more detail

> it develops from three main cell types
>the endoderm forms the epithelium of the mucosa or the lining of the gut tube stuff like liver and pancreas are also associated with the endoderm ie developed there
>the visceral mesoderm surrounds the endoderm, and this will give connective tissue structures and smooth muscle components of the gut tube ie the lamina propria, the muscularis mucosa and the muscularis externa and also the surrounding tissue layers of the submucosa and external connective tissue
>the neural crest cells will form the ENS (which consists of the Meissner’s plexus which is present by week 8 and the Auerbach’s plexus which is present at week 12)

Question 3

where are the mesentries of the gut derived from ?

Answer 3

derived from the mesoderm

and can be divided into the ventral mesenteries and the dorsal mesenteries

Question 4

where do the ventral mesenteries derive from ?

Answer 4

essentially they derive from what’s left of the septum transversum after the liver is done with it

derived from the septum transversum, the liver is going to grow within this structure and as the liver continues to develop the septum transversum will ultimately thin out lead to the remnants of the ventral mesenteries ie the falciform ligament and the lesser omentum

Question 5

where do the dorsal mesenteries derive from ?

Answer 5

> derived from the connection between the visceral part of the lateral plate mesoderm
(this will surround the endoderm of the gut tube) and the somatic part of the end plate mesoderm

>can be divided into three parts :
dorsal mesogastrium (developing stomach, and will form the greater omentum)
dorsal mesoduodenum (will remain intraperitoneal) 
dorsal mesocolon (associated with the large intestine)