GI embryology 1 Flashcards
When does embryonic folding occur?
4th week
What happens during embryonic folding?
Laterally - creates ventral body wall and primitive gut tube becomes tubular.
Cradiocaudally - creates cranial and caudal pockets from yolk sac endoderm (beginning primitive gut development)
What is the gut tube?
Endoderm lined tube Runs the length of the body Blind pouches at the head and tail (no opening here) Opening at the umbilicus Splanchnic mesoderm covering
What are the embryonic divisions of the gut?
Foregut - begins as diverticula
Midgut - opening at first and continuous with yolk sac
Hindgut - begins as diverticula
What is derived from the foregut?
Oesophagus
Stomach
Pancreas, liver and gall bladder
Duodenum (proximal to entrance of bile duct)
What is derived from the midgut?
Duodenum (distal to entrance of bile duct) Jejunum Ileum Cecum Ascending colon Proximal 2/3 transverse colon
What structures have mixed blood supply?
Duodenum and Pancreas
This is because they develop close to the junction between the foregut and midgut.
What is the intraembryonic coelom?
A single cavity that is later subdivided by the future diaphragm into abdominal and thoracic cavities. This is formed as the embryo folds.
There is one membrane lining the whole cavity which eventually specialises to form pericardium and pleural membrane as the cavity specialises.
What are mesenteries?
A double layer of peritoneum suspending the gut tube from the abdominal wall.
Why do we have mesenteries?
Allows a conduit (a channel) for blood and nerve supply
Allows mobility where needed
How do mesenteries develop?
From condensation of the splanchnic mesoderm that surrounds the new gut.
Where are the mesenteries?
Dorsal - whole length of the gut tube from the dorsal body wall.
Ventral - just the foregut
Why do we have greater and lesser peritoneal sacs?
Because the dorsal and ventral mesenteries in the region of the foregut divide the cavity into left and right sacs in this region only.
What are omenta?
Specialised regions of peritoneum.
What is a peritoneal reflection?
A change in direction…
- From parietal peritoneum to mesentery
- From mesentery to visceral peritoneum
- From visceral peritoneum to…