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Flashcards in 10. Embryology 2 Deck (21):

The primary intestinal loop is continuous with the vitelline duct.
True or False?



The distal duodenum is formed from the caudal limb of the primary intestinal loop.
True or False?

formed from cranial limb.


What does the caudal limb of the primary intestinal loop form?

1. Distal ileum
2. Caecum
3. Appendix
4. Ascending colon
5. Proximal 2/3 transverse colon


The intestines develop inside the abdomen during development.
True or False?

herniation of the primary intestinal loop occurs at week 6 due to rapid elongation of the midgut and liver.
There is not enough room in the abdomen.


Describe the rotation of the midgut during herniation.

90* anti-clockwise.
Cranial limb is on right.
Caudal limb is on left.


Describe the rotation of the midgut at week 10 when it returns to the abdomen.

180* anti-clockwise.
Jejunal loops are on left.
Caecum is under liver.
Vitilline duct is destroyed in this process.


The midgut undergoes 180* clockwise rotation in total when it herniates and completely returns to abdomen.
True or False?

270* anti-clockwise.


The caecum is found in the right iliac fossa in humans, however this is not the case initially during development.
How does the final arrangement of the midgut arise?

Caecum descends down the abdomen from the liver to the right iliac fossa.
It pulls down the ascending and transverse colon down with it into the correct arrangement.


Why are the ascending and descending colons described as secondarily retroperitoneal?

The dorsal mesentery of the colons shortens and degenerates, pulling them back against the posterior abdominal wall.


Why might appendicitis pain be felt in different sites for different people?

The appendix is suspended by a mesentery which means that its position around the caecum can vary.
It is usually located retrocaecal (essentially dragged down with caecum during development).


Meckel's/Ileal diverticulum is the most common GI malformation (2% of population).
How does it arise?

Remnant of vitilline duct.
Results in out pocketing of the ileal wall.


How does omphalocele differ from gastroschisis?

Omphalocele = midgut fails to return to abdomen, but still develops in umbilical cord.
Gastroschisis = intestines herniate through a hole in the abdomen wall and develop outside body. No covering.


In some cases people can have the small intestine of the right side of the body and the large intestine on the right.
How does this arise during development?

Failure of the midgut to rotate a further 180* anti-clockwise when it is returning to the abdomen.


What can occur if the midgut rotates abnormally so that areas which should be retroperitoneal remain suspended by a dorsal mesentery?

Twisting (volvulus) of the midgut can occur.
Resulting in:
1. bowel obstruction = bilious vomiting
2. Constriction of arterial supply = infarction


What does the hindgut give rise to?

1. Distal 1/3 transverse colon
2. Descending colon
3. Sigmoid colon
4. Rectum
5. Cranial 2/3 of anal cavity.


Why are our genitals on the front and our anal canal behind?

Ventral part of cloaca forms the bladder, urethra, caudal part of vagina etc.
Dorsal part of cloaca forms anorectal canal.


What germ layer is the anal canal derived from?
What is the significance of this?

Top 2/3 = endoderm
Bottom 1/3 = ectoderm

Seperated by pectinate line.
Different epithelial linings, lymph and blood systems.


What can occur if the urorectal septum fails to completely extend caudally?

Fistulas = abnormal connection between rectum and urethra or vagina.


What happens if the anal membrane fails to degenerate?

No ass hole.
Need surgery to get shit out.


What is the enteric nervous system derived from? (has 2 plexi responsible for muscle contraction and secretion in the GI tract)

Neural crest cells (ectoderm origin)


What can occur if neural crest cells do not migrate to the bowel?

There is no enteric ganglia.
Therefore peristalsis does not occur and all the shit builds up in ur bowel and you get a fattt belly.
Have to remove the affected bowel and connect the remaining healthy bowel to the anus,