Embryology And Anatomy ✅ Flashcards
When does the human GI tract first appear?
4 weeks gestation
When is the human GI tract complete?
12 weeks gestation
What does the embryo consist of at 4 weeks gestation?
3 parts - the endoderm, ectoderm, and mesoderm
What does the endoderm give rise to in the GI tract?
The lining of the GI tract
What does the mesoderm give rise to in the GI tract?
The smooth muscle
What does the ectoderm give rise to in the GI tract?
The enteric nervous system
How is embryonic folding involved in the formation of the GI tract?
Initial folding results in a tubular structure with craniocaudal distribution. Further folding results in the cranial and caudal sections forming into blind-ended tubes
What do the blind-ended tubes formed in embryonic folding later become?
The foregut and hindgut
What separates the blind-ended tubes that later become the foregut and hindgut?
A section which is still attached to the yolk sac
What does the section that is still attached to the yolk sac later become?
The midgut
What happens to the yolk sac as the embryo develops further?
The yolk sac becomes smaller, and the midgut becomes a separate structure
Is the midgut still attached to the yolk sac when it becomes a separate structure?
Yes
How is the midgut still attached to the yolk sac after it becomes a separate structure?
Via the Vitelli email duct
What structures are formed from the foregut?
- Pharynx
- Oesophagus
- Stomach
- Proximal duodenum
What structures are formed from the midgut?
- Distal duodenum
- Small bowel
- Distal colon
What structures are formed from the hindgut?
- Distal colon
- Rectum
What happens to the intestines throughout development?
It undergoes a number of changes in position
What happens to the intestines at week 5?
It elongates and begins to form a loop, which protrudes into the umbilical cord
What has happened to the position of the GI tract by week 6?
The stomach and duodenum have rotated 90 degrees clockwise
What happens to the intestines at week 8?
The duodenum and jejunum herniate further from the abdominal cavity, and rotate around the axis of the superior mesenteric artery by 90 degrees, and take up a position behind the superior mesenteric artery
What direction does the duodenum and jejunum rotate around the axis of the superior mesenteric artery?
Counterclockwise
What happens to the intestine at week 11?
The intensive retracts into the abdomen
What is the control mechanism behind the intestine retracting into the abdomen at week 11?
Unknown
In what order does the intestine return to the abdomen in week 11?
The jejunum returns first, then ileum, then rest of small intestine, then colon
Where in the abdomen does the jejunum return to?
The left half
Where in the abdomen does the ileum return to?
The right half
What happens to the position of the intestines by the end of week 11?
The caecum has moved downwards and the intestines have reached their final adult position
When does the intestinal endoderm begin to differentiate?
Only after the final position of the intestines is reached (aka after week 11)
