5. Embryology - Development Of The Midgut And Hindgut

Question 1

What forms the primary intestinal loop?

Answer 1

Elongation of the midgut, runs out of space and so forms a loop.

Question 2

What is at the axis of the primary intestinal loop?

Answer 2

Superior mesenteric artery

Question 3

How is the primary intestinal loop connected to the yolk sac?

Answer 3

Via the vitelline duct.

Question 4

What limbs are connected to the primary intestinal loop?

Answer 4

Cranial and caudal.

Question 5

What happens at the 6th week due to the quick growth of the liver and the primary intestinal loop?

Answer 5

Intestine herniated into the umbilical cord.

Question 6

What happens to the orientation of midgut structures in the first 90 degree anticlockwise rotation in an embryo?

Answer 6

Cranial and caudal limbs now on lateral sides of the superior mesenteric artery, small intestine begins to form in the cranial limb.

Question 7

What part of the GI tract is formed from the cranial limb of the primary intestinal loop?

Answer 7

Jejunum and cranial portion of the ileum.

Question 8

What part of the GI tract is formed from the caudal limb?

Answer 8

Cecum, appendix, caudal portion of the ileum, ascending colon, and proximal two-thirds of the transverse colon.

Question 9

What happens to the orientation of midgut structures in the second 90 degree anticlockwise rotation in an embryo?

Answer 9

Cranial limb now inferior to superior mesenteric artery and caudal limb superior. So small intestine crossing under the superior mesenteric artery and cecal swelling developing in caudal limb.

Question 10

What happens to the orientation of midgut structures in the third 90 degree anticlockwise rotation in an embryo?

Answer 10

Caudal and lateral limbs now on opposite lateral sides of the superior mesenteric artery. Transverse colon develops from caudal limb.

Question 11

What structures does descent of the caecal bud after midgut rotation form?

Answer 11

Ascending colon and cecum.

Question 12

What is an incomplete rotation defect?

Answer 12

Midgut loop makes only one 90degree rotation, leading to a left sided colon.

Question 13

What is a reversed rotation?

Answer 13

Midgut loop makes one 90 degree rotation clockwise, so the transverse colon passes posterior to the duodenum.

Question 14

What can happen as a result of a midgut defect?

Answer 14

Volvulus (twisting of the intestine) leading to strangulation and ischaemia.

Question 15

What is a vitelline cyst?

Answer 15

Vitelline duct persists forming fibrous strands with a cyst in the centre.

Question 16

What is a vitelline fistula?

Answer 16

Vitelline duct persists forming a direct communication between the umbilicus and intestinal tract.

Question 17

What is a meckel’s diverticulum?

Answer 17

Vitelline duct persists, forms an ileal diverticulum with or without fibrous strands teaching the diverticulum to the abdominal wall.

Question 18

What is the rule of 2’s for meckel’s diverticulum?

Answer 18

Occurs in 2% of the population.
Is 2 feet from the ileocaecal valve.
Usually detected in under 2s.
2:1 ration male:female.

Question 19

What two types of ectopic tissue can a meckel’s diverticulum contain?

Answer 19

Ectopic gastric or pancreatic tissue.

Question 20

What can leads to atresia or stenosis of the oesophagus, bile duct and small intestine?

Answer 20

Wholly or partially unsuccessful recanalisation in response to rapid cell growth partially or completely obliterating the lumen.

Question 21

Where do most GI atresias and stenosis’ occur?

Answer 21

Duodenum.

Question 22

What causes pyloric stenosis?

Answer 22

Hypertrophy of the circular muscle in the region of the pyloric sphincter (not recanalisation failure).

Question 23

What characteristic symptom in infants does pyloric stenosis cause?

Answer 23

Projective vomiting.

Question 24

What is gastroschisis?

Answer 24

Failure of closure of the abdominal wall during folding of the embryo, leading the gut tube and its derivatives outside the body cavity.

Question 25

What is omphalocoele?

Answer 25

Abdominal wall defect in which the intestines, liver and occasionally other organs remain outside of the abdomen in a sac which is formed from an out-pouching of the peritoneum protruding through the umbilicus.

Question 26

What is an umbilical hernia?

Answer 26

Outpouring of the intestines with covering of skin and subcut tissue through umbilicus.

Question 27

What divides the anal canal into histologically distinct superior and inferior parts?

Answer 27

Pectinate line.

Question 28

What structures are different on the different in the superior and inferior parts of the anal canal?

Answer 28

Arterial supply, venous and lymph drainage, innervation, different epithelium types.

Question 29

What is the proctodeum?

Answer 29

Junction between the two embryonic derm layers that is ectoderm on endoderm of the hindgut and forms the anal pit.

Question 30

What is the arterial supply, innervation, epithelium type and lymph drainage of the anal canal superior to the pectinate line?

Answer 30

Inferior mesenteric artery.
Visceral innervartion - S2,3,4 pelvic parasympathetics.
Columnar epithelium.
Lymph drains to internal iliac nodes.

Question 31

What is the arterial supply, innervation, epithelium type and lymph drainage of the anal canal inferior to the pectinate line?

Answer 31

Pudendal artery.
Somatic innervation - S2,3,4 pudendal nerve.
Stratified epithelium.
Lymph drains to superficial inguinal nodes.

Question 32

What sensation is possible in the anal canal above the pectinate line due to the contribution of two embryonic tissues to the anal canal?

Answer 32

Only stretch.

Question 33

What sensation is possible in the anal canal below the pectinate line due to the contribution of two embryonic tissues to the anal canal?

Answer 33

Temperature, touch and pain sensitive.

Question 34

Give 2 hindgut abnormalities (can be linked to cloaca abnormalities)

Answer 34

Imperforate anus.
Anal/anorectal agenesis.
Hindgut fistulae.