Embryology

Question 1

Divisions of foregut, midgut, hindgut

Answer 1

Foregut- up to first half of duodenum. Includes liver, binary apparatus and pancreas.
Midgut- second half of duodenum to proximal 2/3rd transverse colon. Includes caecum and appendix.
Hingut- Distal 1/3 transverse colon to proximal 2/3 rectum.

Question 2

What do the epiblast and hypoblast (bilaminar disc) turn into?

Answer 2

Epiblast- ectoderm
Hypoblast- endoderm
In between the two layers a mesoderm forms from migrating cells of the epiblast.

Question 3

What layer forms the GI tract

Answer 3

Endoderm

Question 4

Describe the development of the gut tube.

Answer 4

Due to different rates of growth longitundal and lateral folding occurs forming a tube from the flat trilaminar disc. The yolk sac gets lose off like a purse string with the longitudnal folding. This process creates the 3D form

Question 5

Anything mucosal has its embryological origin in which layer?

Answer 5

Endoderm.

Question 6

Two gut tube openings

Answer 6

Oropharangeal membrane
Cloacal membrane
Both ectoderm

Question 7

Describe two pathologies related to gut tube formation

Answer 7

Congenital hiatal hernia- If the oesophagus does not elongate the stomach can herniate into the thorax.
Tracheooesophageal atresia/ fistula. Because the trachea buds off the gut tub there can be an opening left behind (fistula). An atresia is a blockage in the oesophagus (blind ended tube)

Question 8

Foregut sits between?

Answer 8

The dorsal and ventral mesogastrium (mesentery)

Question 9

Describe the rotation of the stomach and what happens to the mesenteries.

Answer 9

The stomach rotates 90 degrees on its long axis clockwise. This brings the dorsal mesogastrium to the left and the ventral to the right. Dorsal boundary becomes greater curvature, ventral becomes the lesser.

Question 10

Congenital hypertrophic pyloric stenosis

Answer 10

A thickening in the muscle layer around the pyloric sphincter blocking flow of chyme into the duodenum. (Can be caused in adults by ulcerations)

Question 11

Describe the formation of the liver and biliary system

Answer 11

Ventral outgrowth in gut tube forms hepatic diverticulum. Divides in two as it grows forming liver and gallbladder and ducts within the ventral mesogastrium.

Question 12

Describe formation of the pancreas

Answer 12

Two buds one in ventral mesogastrium, one in dorsal mesogastrium. As the stomach rotates 90 degrees clockwise the duodenum twist the opposite way and the dorsal and ventral pancreatic ducts fuse.

Question 13

Falciform ligament

Answer 13

Part of ventral mesogastrium going the liver to the body wall

Question 14

Describe the twisting of the midgut

Answer 14

Midgut herniates into umbilical opening (vitalliene duct) and then twist anticlockwise 270 degrees around the SMA. It retracts back into the abdomen.
Cecum and appendix rotate into lower right quadrant.

Question 15

Development of hindgut urogenital structures

Answer 15

Cloaca, distal region of the hind gut, expands and a urorectal septum forms splitting the cloaca into the rectum and urogenital sinus.

Question 16

Hirschprungs disease

Answer 16

Absence of neuronal ganglion in affected part. No peristalsis, gut content stasis

Question 17

Meckels diverticulum

Answer 17

Where the ileum herniates into the remnant of vitalliene duct

Question 18

Umbilical hernia (omphalocele)

Answer 18

Where gut herniates outside of body wall through weakened region in body wall.