3 - Embryology of the Mid/Hind Gut

Question 1

What are the names of the blind diverticula in the body?

Answer 1

• Buccopharyngeal membrane
• Cloacal membrane

Question 2

What does the midgut give rise to?

Answer 2

Connected to the yolk sac at its midpoint

Question 3

What is physiological herniation and why does it occur?

Answer 3

• Midgut elongates as well as liver so intestines are pushed out of umbilicus as no room in abdominal cavity.
• SMA axis and is connected to the yolk sac by vitelline duct
• Cranial and caudal limbs around the SMA

- 270 degree rotation as it herniates in and out

• Herniates in week 6 and returns in week 10

Question 4

What is the relationship between the transverse colon and the duodenum?

Answer 4

Transverse colon is mobile and sits anterior to duodenum, which is retroperitoneal and immobile

Question 5

What happens to the organs that make up the cranial limb?

Answer 5

Cranial limb returns to the body first, so it’s organs go to the left side. This is the jejunum and the ileum

Question 6

What is the caecal bud?

Answer 6

Distal part of midgut loop develops a caecal bulge, proximal part becomes convoluted. Grows down to the right iliac fossa to form the ascending colon

Question 7

What are some congenital issues that can occur with malrotation and reverse rotation of the midgut loop?

Answer 7

- Left sided colon: only on 90 degree rotation

- Posterior transverse colon: reverse rotation

Can lead to volvulus, which leads to strangulation and ischaemia

Question 8

What are some issues that can occur with the vitelline duct?

Answer 8

Fistula will leak intestinal contents, unlike patent urachus which is urine

Question 9

What is Meckel’s diverticulum and what is the issue with this congenital defect?

Answer 9

• In the ileum, can contain ectopic gastric or pancreatic tissue which can cause inflammation and issues
• Persistent yolk sac remnant

Question 10

When does an umbilical hernia occur?

Answer 10

When there is a large opening between the umbilical cord and the abdominal cavity. Will be present at birth

Question 11

Where does recanalisation of the gut tube occur and what are some issues that can occur with this?

Answer 11

- Oesophagus, bile duct, small intestine

• Week 6-8 recanalised
• May end up with atresia or stenosis
• Usually in duodenum due to incomplete recanalisation (higher) or vascular accidents (lower)

Question 12

What is pyloric stenosis and how does it present?

Answer 12

• Not recanalisation failure it is hypertrophy of the circular muscle in the pyloric sphincter
• Causes projectile vomiting and can palpate in infants

Question 13

What is the difference between omphalocoele and gastroschisis?

Answer 13

• O is incomplete physiological herniation. Not like umbilical hernia as not covered by skin and subcut
• G is due to failure of the abdominal wall to close during folding of the envelope. No covering

Question 14

What does the hindgut give rise to?

Answer 14

Question 15

How does the anal canal have different embryological derivatives?

Answer 15

• Cloacal membrane ruptures and the proctodaeum surrounds the outer anal canal so ectoderm makes up the inferior anal canal
• Superior anal canal from hind gut
• Split by pectinate line

Question 16

What is the nerve supply and lymphatic drainage of the anal canal?

Answer 16

Question 17

What does the different nerve supply mean for feeling pain in anal canal?

Answer 17

• Above pectinate line can only feel stretch as visceral innervation
• Below line sensitive to temperature, touch and pain as somatic innervation

Question 18

What are some congenital hindgut abnormalities that can occur?

Answer 18

- Imperforated anus: cloacal membrane doesn’t rupture

- Hind gut fistula: issue with urorectal septum

Question 19

What structures in the whole gut retain their mesenteries?

Answer 19

Question 20

What organs are part of the caudal and cranial limbs?

Answer 20

Question 21

What parts do the dorsal and ventral mesenteries split into?

Answer 21

Question 22

What is the innervation of the mid and hind gut?

Answer 22

Question 23

In general, summarise the timeline for gut development.

Answer 23

Question 24

The pancreas is derived from two portions, what do each of these portions become?

Answer 24

Dorsal: most of the gland

Ventral: duct system

Question 25

How is the cloaca split?

Answer 25

The urorectal septum splits it into a urogenital sinus and a anorectal canal

Question 26

Why is pain in appendicitis originally felt in the periumbilical area and then the right iliac fossa?

Answer 26

• Reffered pain - it is a midgut structure so innervates by T6-T12 which correlates to the periumbilical area
• When appendix irritates the parietal peritoneum this has somatic innervation leading to pain where the inflammation actuall is

Question 27

How does the transverse mesocolon form?

Answer 27

Fusion with greater omentum will incorporate the transverse colon.