2 - Embryology of the Foregut Flashcards
What is the gut tube?
Development in week 3
- Endoderm internal lining with blind pouch at head and tail
- Splanchnic mesoderm external lining
- Opening at umbilicus where yolk sac comes in to form gut tube
What are the parts of each gut and what organs do they go onto form in the body?
What is the blood supply to each area of the primitive gut?
The structures close to junctions have mixed blood supply
Why do the duodenum and the pancreas have a mixed blood supply?
What is the importance of the intraembryonic coelom?
- Space between lateral plate
- Subdivides into abdominal and thoracic cavities by the diaphragm
- Membrane lining the cavity specialise to become pleura, pericardium and peritoneum
What are the two main mesenteries in the abdominal cavity?
- Dorsal mesentry suspends entire gut tube from dorsal body wall
- Mesenteries are double layers of peritoneum allowing mobility and a conduit for blood and nerve supply. Formed from splanchnic mesoderm
Where are the greater and lesser sacs and how are they formed?
- Dorsal and ventral mesenteries in foregut divide cavity into left and right
- L: greater sac
R: lesser sac behind stomach
- Due to rotation of the stomach
What are the omenta?
- Specialised regions of peritoneum
- Greater: dorsal mesentery
- Lesser: ventral mesentery (only foregut)
What are the consequences of the rotation of the stomach?
What is a peritoneal reflection?
Change in direction from parietal peritoneum to mesentry and from visceral to mesentry
What are structures classified as if they are not suspended in the abdominal cavity and therefore have no mesentry?
- Retroperitoneal: were never in cavity and never had mesentry
- Secondarily retroperitoneal: begin development in cavity and had a mesentry but with growth the mesentry is lost by fusion to the posterior abdominal wall as organs pushed up against back. Can be mobilised
How does the gut tube split into a GI and a respiratory tract?
- Foregut (lung bud to liver bud)
- 4th week respiratory diverticulum in ventral wall of foregut at junction with pharnygeal gut
What are some birth defects that can arise from the embryological separation of the oesophagus and the trachea?
If the tracheoesophageal septum is in an abnormal position can end up with fistulas and baby is unable to feed and will go blue.
What is the embryological origin of the glands of the foregut?
- Liver and Billiary system: ventral mesentry
- Pancreas (Mid and Foregut): uncinate and inferior head from ventral mesentry. The rest from the dorsal mesentry
What relations does the peritoneum have to the liver?
- Lesser omentum sits posteriorly attaching lesser curve of stomach to the liver
- Coronary ligament anteriorly between diaphragm and liver
- Falciform ligament separates left and right lobes and at the end the ligamentum teres arises and attaches liver to anterior body wall
Why is the duodenum secondarily retroperitoneal?
- From foregut and midgut
- Shape determined by rotation of stomach, pushes it to right from anerior, against posterior body wall losing it’s mesentry
- Fusion fascia (double layered peritoneum)
What is a summary of the embryology of the foregut tube and the stomach?
Where does the foregut end blindly?
- Oropharyngeal membrane
- Cloacal membrane
- Breaks down to form future mouth and anus
Is there always a lumen in the digestive tract?
No - in 5th/6th week the endoderm (especially in duodenum) proliferates to form solid tube. Recanalised at the end of the embryonic period
How does the pancreas develop?
- Dorsal and ventral pancreatic bud
- Rotation of stomach causes ventral bud to go round the back of the duodenum and join the doral bud.
