GI embryology 2

Question 1

What does the midgut give rise to?

Answer 1

Small intestine, including most of duodenum (up to bile duct). Caecum and appendix. Ascending colon, 2/3 of transverse colon

Question 2

The midgut of the primary intestinal loop grows lots, what happens when it runs out of space?

Answer 2

Makes a loop that:

• Has the Superior mesenteric artery as its axis
• Is connected to the yolk sac by the vitalise duct
• Has cranial and caudal limbs

Question 3

What is physiological herniation?

Answer 3

During 6th week, growth of the primary intestinal loop is very rapid (elongation) and the liver is also growing very rapidly.
This means the abdominal cavity is too small to accommodate both so the intestines herniate into the umbilical cord.

Question 4

How much does the midgut rotate?

Answer 4

Undergoes 3 90 degree turns and then the caecal bud descends.

Question 5

What is the purpose of the three rotations?

Answer 5

To make sure that the cranial limb returns to the abdominal cavity first, moving to the left side.

Question 6

What are the two ways in which rotation can go wrong?

Answer 6

-Incomplete rotation - midgut loop makes only one 90 degree rotation. This means left sided colon.

Reversed rotation - Midgut loop makes one 90 degree rotation clockwise. This means that the transverse colon passes posterior to the duodenum.

Question 7

What risks are associated with midgut defects?

Answer 7

Most complications present in neonatal period.

Cause a vulvulus which consul results in Strangulation or Ischaemia.

Question 8

What is it called if the yolk stalk remains?

Answer 8

Vitelline stalk

Question 9

What are the possible complications of a persistent vitelline duct?

Answer 9

Vitelline cyst - when the vitelline duct forms fibrous stands.
Vitelline fistula - Direct communication between the umbilicus and intestinal tract
Meckel’s diverticulum - ideal diverticulum. This is the most common GI anomaly.

Question 10

What is Meckel’s diverticulum?

Answer 10

a congenital outpouching or bulge in the lower part of the small intestine.
Rule of 2s;
2% of population
2 feet away from ileocaecal valve
Usually detected in under 2s
2:1 ratio in males / females.

Question 11

What can Meckel’s diverticulum contain?

Answer 11

Ectopic gastric or pancreatic tissue.

Felt as midgut pain as innervated by lesser splanchnic nerve because it develops from the midgut.

Question 12

What is recanalisation?

Answer 12

This happens in oesophagus, bile duct and small intestine.
Lining of gut thickens so lumen becomes narrow. Recanalisation occurs here to clear the lumen.
If not, cause atresia or stenosis.
Most artesian and stenoses occur in the duodenum

Question 13

Define atresia

Answer 13

Lumen obliterated

Question 14

Define stenosis

Answer 14

Lumen narrowed

Question 15

What is pyloric stenosis?

Answer 15

Narrowing of pyloris (a circular muscle in the region of the pyloric sphincter) of the stomach.

This occurs because the smooth muscle of the pyloric sphincter has hypertrophied. So, it is not due to recanalisation.

It is a common abnormality if the stomach in children.

Question 16

How does pyloric stenosis present?

Answer 16

Characteristic projectile vomiting

Question 17

What is gastroschisis?

Answer 17

Failure of closing of the abdominal wall during folding of the embryo.
This leaves the gut tube and derivatives outside the body cavity.

Question 18

What is Omphalocoele?

Answer 18

Also bowel loop sitting outside of body cavity.
Persistence of physiological herniation.

Differs from umbilical hernias because hernia has covering go skin and submit tissue.

Worse because normal development hasn’t finished.

Question 19

What does the hindgut give rise to?

Answer 19

Distal 1/3 transverse colon, descending colon, rectum, superior part of anal canal. epithelium of urinary bladder.

Question 20

How is the anal canal divided?

Answer 20

Divided by pectinate line into histologically distinct superior and inferior parts.
This indicates differences in aterial supply, venous and lymphatic drainage and innervation.

Question 21

How is anal canal derived?

Answer 21

The inside of the anal canal is derived form hindgut so, because this is derived from the primitive gut tube, it has visceral innervations.

The outside of the anal canal is derived from the proctodeum (anal pit) which is made from ectoderm (like skin) so it has somatic innervation.

Question 22

What innervates the anal canal above the pectinate line?

Answer 22

Visceral - Only stretch senses

Question 23

What innervates the anal canal below the pectinate line?

Answer 23

Somatic innervation

Question 24

What are the consequences of the different types of innervation?

Answer 24

Above - only stretch

Below - temperature, touch, pain sensitive.

Question 25

Where is visceral pain felt from different areas of the gut?

Answer 25

Foregut - epigastrium Midgut - periembilical Hindgut - suprapubic

Question 26

What are some hindgut abnormalities?

Answer 26

Imperforate anus - failure of anal membrane to rupture Anal / anorectal agenesis Hindgut fistulae

Question 27

What structures are mesenteries retained by?

Answer 27

``` Jejunum Illeum Appendix Transverse colon Sigmoid colon ```

Question 28

What structures fo the midgut / hindgut have fused mesenteries?

Answer 28

Duodenum Ascending colon Descending colon Rectum (no peritoneal covering in distal 1/3)