10. Embryology 2

Question 1

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

Answer 1

TRUE

Question 2

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

Answer 2

FALSE

formed from cranial limb.

Question 3

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

Answer 3

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

Question 4

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

Answer 4

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.

Question 5

Describe the rotation of the midgut during herniation.

Answer 5

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

Question 6

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

Answer 6

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

Question 7

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

Answer 7

FALSE

270* anti-clockwise.

Question 8

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?

Answer 8

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.

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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).

Question 11

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

Answer 11

Remnant of vitilline duct.

Results in out pocketing of the ileal wall.

Question 12

How does omphalocele differ from gastroschisis?

Answer 12

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.

Question 13

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?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

What does the hindgut give rise to?

Answer 15

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

Question 16

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

Answer 16

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

Question 17

What germ layer is the anal canal derived from?

What is the significance of this?

Answer 17

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

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

Question 18

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

Answer 18

Fistulas = abnormal connection between rectum and urethra or vagina.

Question 19

What happens if the anal membrane fails to degenerate?

Answer 19

No ass hole.

Need surgery to get shit out.

Question 20

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

Answer 20

Neural crest cells (ectoderm origin)

Question 21

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

Answer 21

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,