Embryology - midgut development

Question 1

Normal midgut layout

Answer 1

Ascending colon is lateral to small bowel
Small bowel central
Large bowel peripheral

Question 2

How does the midgut start to develop around week 6?

Answer 2

Midgut elongates rapidly forming intestinal loop
Liver is developing at the same time as this so there is not enough space inside cavity - bowel herniates out into umbilical cord

Question 3

What is the axis for the developing midgut? (what it rotates around)

Answer 3

Superior mesenteric artery

Question 4

Describe rotation of the midgut

Answer 4

Cranial side elongates and forms loops of small bowel
Caudal side is future large bowel

Rotates 90 degrees anticlockwise 3 TIMES
Mean caudal end (large bowel) ends up lateral and anterior to and cranial small bowel

Question 5

What week does physiological herniation occur?

Answer 5

Week 6

Question 6

What week does the physiological herniation return to abdominal cavity?

Answer 6

Week 10

Question 7

What else happens while midgut is rotating?

Answer 7

Caecum bulge forms at top of caudal end
This rotates 3x anticlockwise = final place is R iliac fossa

Question 8

two midgut rotational developmental problems

Answer 8

Malrotation
Reversed rotation

Question 9

What happens in malrotation?

Answer 9

There is only 1 90 degree anticlockwise rotation
Large bowel (caudal end) ends up on left side

Question 10

what is reversed rotation?

Answer 10

1x 90 degree rotation CLOCKWISE - transverse colon ends up lying behind of small intestine

Question 11

Omphalocele - what causes

Answer 11

Failure of midgut to return to abdominal cavity, remain within umbilicus

Question 12

What does umbilicus covering of omphalocele mean?

Answer 12

Have a peritoneal covering - not exposed to inflammatory amniotic fluid so gut develops fairly normally and feeding can commence

Question 13

Problem with omphalocele

Answer 13

Signals other genetic developmental abnormalities - mortality rate is high for these

Question 14

What is gastroschisis due to?

Answer 14

Failure of abdominal ventral (anterior) wall to develop properly - lateral folding is incomplete

Question 15

What does the failure in abdo wall mean for cavity contents?

Answer 15

Herniated contents are not covered by peritoneum and are exposed to inflammatory amniotic fluid - negatively affects gut development

Question 16

Good thing about gastroschisis

Answer 16

Mortality rate lower than omphalocele - less other genetic problems

Question 17

Types of vitelline duct abnormalities

Answer 17

Vitelline cyst
Vitelline fistula
Meckel’s diverticulum

Question 18

What is vitelline cyst?

Answer 18

Patent middle section of vitelline duct - but no direct open pathway to umbilicus from midgut

Question 19

What is vitelline fistula?

Answer 19

Connection between umbilicus and midgut - could see faeces coming out of umbilicus

Question 20

What is Meckel’s diverticulum?

Answer 20

Outpouching of vitelline duct on midgut - almost like 2nd appendix

Question 21

Rules with meckel’s diverticulum

Answer 21

Rules of twos:

2% of population have it
Located 2 feet proximal to ileo-caecal valve
Detected in under 2’s
2:1 ratio male to female

Question 22

What causes recanalisation failure?`

Answer 22

When midgut develops, there is rapid proliferation of endoderm which temporarily occludes lumen.
This usually recanalises but can fail

Question 23

What causes recanalisation failure?`

Answer 23

When midgut develops, there is rapid proliferation of endoderm which temporarily occludes lumen.
This usually recanalises but can fail

Question 24

Degrees of recanalisation failure

Answer 24

Partial - stenosis of midgut tube

Unsuccessful - atresia (full blockage)

Question 25

What part of the bowel does recanalisation failure often affect most?

Answer 25

Duodenum