Embryology Flashcards
Which germ layers is the GI tract formed from?
Endoderm = Lining of gut tube
Visceral Mesoderm = Muscle layers etc.
What are the dorsal mesenteries, and which structure are they associated with?
Dorsal mesogastrium = Stomach
Dorsal mesoduodenum = Duodenum. Proximal part retains its mesentery, rest becomes retroperitoneal
Mesentery proper
Dorsal mesocolon = Transverse and sigmoid retain their mesenteries, rest becomes retroperitoneal during development
What are the ventral mesenteries?
Lesser omentum
Falciform ligament
What does the dorsal mesogastrium give in the adult?
Greater omentum
At which point does the oesophagus become distinguishable?
End of week 4
At which points do the circular and longitudinal muscles of the oesophagus develop?
Circular = Week 5 Longitudinal = Week 8
How does the stomach develop?
Dilation of caudal part of the foregut
Dorsal border grows paisley, forming greater and lesser curvatures
Causes bending of the tube
Stomach rotates 90 degrees about both longitudinal and AP axis
Formation of vacuoles helps accommodate rotation of the stomach
How does stomach growth affect omenta?
Growth and rotation of the stomach creates lesser sac and causes dorsal mesentery to bulge
Continued growth of dorsal mesentery forms greater momentum
Lesser omentum and falciform ligament form from ventral mesentery
From which parts of the gut tube to the individual parts of the duodenum form?
Parts 1 and 2 of duodenum = Caudal portion of foregut
Parts 3 and 4 of duodenum =
Cranial portion of midgut
How does stomach growth affect the duodenum?
Duodenal loo is directed to the right due to rotation of the stomach
From which layers does the liver develop?
Endoderm (from duodenum) = Liver cells and lining of biliary tree
Septum transversum = Hematopioetic cells, Kupffer cells, connective tissue
Into where does the liver bud grow?
Mesoderm of Septum Transversum
Why is the growth of the liver disproportionally rapid at the early stages of development?
Allows for production of red blood cells
Which two components make up the embryonic pancreas?
Ventral and dorsal pancreatic buds
How does the pancreas develop?
Th ventral pancreatic bud migrates around the duodenum to get to the final adult position alongside the dorsal pancreatic bud
The two buds will fuse over time and form one communication with the duodenum
What is an annular pancreas?
Solid glandular tissue of the ventral pancreatic duct surrounds the duodenum
Can cause construction and narrowing/stenosis of the duodenum
From where does the spleen originate?
Mesoderm derivative (not form the gut tube)
When does the spleen start to develop?
5th week
What change in function does the spleen undergo sprung development?
Initially haematopoetic
Develops into lymphatic organ during weeks 15-18
What is the appearance of the spleen during development?
Lobular appearance
Lobes normally regress before birth
Which organs are associated with the midgut?
Second half of the duodenum Jejunum Ileum Caecum and appendix Ascending colon Proximal 2/3 transverse colon
How does the midgut’s communication with the yolk sac develop?
Start of week 4 = Communicates with yolk sac along its length
This connection narrows until the vitelline duct has formed
What happens to the midgut around week 5 of development?
The midgut has outgrown the embryo and bulges ventrally (physiological hernia through the umbilicus)
How does the midgut rotate during development?
Rotates 90 degrees around axis of SMA
Caudal limb is on the left, cranial on the right
Caecal bud forms on causal limb
What growth happens to the midgut whilst outside of the abdominal cavity?
Small insetting starts to fold o itself
Jejunal-ileal loops form
Caecum sprouts an appendix
When does the midgut return to the body cavity?
Week 10
What happens during the midguts return to the body cavity?
Small intestine returns first Further 180 rotation Jejunum displaced left and ileum right Descending colon pushed left Transverse colon pushed superiorly Caecum is last to re-enter
What is Meckel’s Diverticulum?
Persistent attachment of the small intestine to the umbilicus
What are the defects of the small intestine?
Vitelline Fistula
Vitelline Cyst
Vitelline Ligament
Meckel’s Diverticulum
What is the cloaca?
An expansion of the endoderm which gives rise to the hindgut
What is the purpose of the urorectal septum?
Divides the cloaca into the part which ill give rise to the handgun, and the part which will give rise to the urogenital system
How does the definitive gut lumen develop?
At week 5/6, there is proliferation of mucosa and thehollow gut tube becomes occluded
Vacuoles develop of the next 2 weeks
Recanalisation is complete by week 9
