Development of the GI Tract

Question 1

What is the name given to the embryo @ 3 weeks?

What is this tissues shape?

Answer 1

A blastocyte.

It is a flattened, tri-laminar disc.

Question 2

What are the X3 layers of the blastocoele tri-laminar disc from top to bottom?

Answer 2

Top = epiderm (ectoderm)
Middle = mesoderm
Bottom = endoderm

Question 3

What cavity does the epiderm form?

Answer 3

The amniotic cavity.

Question 4

What cavity does the endoderm form?

Answer 4

The yolk sac.

Question 5

How does the tri-laminar disc fold as it develops?

Answer 5

It folds under cranially, caudally and laterally incorporating and eventually “pinching off” part of the yolk sac.

Question 6

What is the name of the cavity that traps the gut and will eventually become the peritoneal cavity?

Answer 6

The coelomic cavity.

Question 7

What is the name of the duct which connects the yolk sac to the developing umbilicus?

Answer 7

The vitelline duct.

Question 8

What structure eventually becomes the bladder, with its remnants connecting it to the umbilicus?

Answer 8

The allantois.

Question 9

What is the allantois remnant called which connects the bladder to the umbilicus?

Answer 9

The remnants of urachus.

Question 10

What is an atresia?

Answer 10

An absence or an abnormal narrowing of a passage/tube in the body.

Question 11

What is a fistula?

Answer 11

A connection between two hollow spaces where one should not be.

Question 12

How does the pancreas form?

Answer 12

It forms as X2 separate hepatic diverticular “buds” called the dorsal and ventral buds.

Question 13

Which pancreatic bud is smaller and rotates into place?

What pathway does it take when rotating?

Answer 13

The ventral bud.

It rotates behind the duodenum due to the stomach rotating clockwise and both parts fuse.

Question 14

What is the name of the condition where the ventral pancreas forms a ring around the duodenum as it develops?

Answer 14

Annular pancreas.

Question 15

What is the full name of the appendix?

Answer 15

The veriform (work-like) appendix.

Question 16

How do the intestines get their positions during development?

Answer 16

The enlarging liver causes the midgut to herniate towards the vitelline duct and the loop of midgut rotates 180 degrees anti-clockwise (looking face on) around the vitelline axis. The midgut is then bough back into the abdominal cavity and the vitelline duct sealed off.

Once back in the abdomen the whole contents rotates once more to bring the ceacum from the top right to bottom right.

Question 17

What is a vitelline duct which remains and does not reduce called?

Answer 17

Meckle’s diverticulum.

Question 18

What is the name of the condition if stage 3 of rotation fails?

What is potentially dangerous about this?

Answer 18

Malrotation of the gut.

The ceacum (with its mesoceacum) ends up at the position of the hepatic flexure, and the mesoceacum can compress the duodenum.

This is called LADD’s band.

The ileoceacal junction and the duodenojejunal junction are now also close together which can end up rotating around each other causing a VOLVULUS.

Question 19

What other types of rotation issues can occur?

Answer 19

• non-rotation

- reversed rotation

Question 20

What is the name of the condition where the gut never returns to the abdominal cavity?

Answer 20

An omphalocele.

Question 21

What birth defect sees the gut protrude through the right side of the anterior abdominal wall?

Answer 21

A gastroschisis.

Question 22

Where does hindgut stop? What does it give rise up to?

What is the name of the line which makes this change in embryology?

Answer 22

It gives rise up to the superior/proximal part of the anal canal. The distal part is proctodeum.

The pectinate line.