Embryology of the GI

Question 1

What layer of the trilaminar disc forms the gastro intestinal tract?

Answer 1

The embryonic endoderm

Question 2

What layer of the trilaminar disk forms muscles?

Answer 2

The embryonic mesoderm

Question 3

What membranes close the gut tube at the cranial end and the caudal end?

Answer 3

Cranial- oropharyngeal membrane
Caudal- cloacal membrane

Question 4

What part of the mesentry connects the gut tube to the dorsal body wall? ( lower part of the Oesophagus to the cloacca )

Answer 4

Dorsal mesentery

Question 5

What are the two parts of the ventral mesentry?

Answer 5

Falciform ligament - attaches the liver to the abdominal wall
Lesser omentum - holds the liver to the gut tube (stomach and duodenum)

Question 6

What do we call the area of the liver attached to the diaphragm?

Answer 6

The bare area of the liver

Question 7

What does secretion of (SHH) sonic hedge hog by the gut endoderm cells cause?

Answer 7

HOX gene expression in the gut mesoderm, varying amounts of the HOX gene causes cranio caudal organization of the gut

Question 8

What is mesentery structurally?

Answer 8

A double layer of peritoneum

Question 9

Where does the foregut extend from and extend to?

Answer 9

From the lung bud diverticulum to the bile duct opening of the duodenum

Question 10

How is the stomach formed by the foregut in week 4?

Answer 10

The foregut caudal to Oesophagus dilates. Also 90° clockwise rotation around a longitudinal axis

Question 11

What is the second rotation of the newly developing stomach?

Answer 11

A rotation along the antero-posterior axis

Question 12

Which nerves supply which parts of the stomach due to this rotation?

Answer 12

The right vagus nerve supplies the posterior and the left vagus nerve supplies the anterior wall

Question 13

What is the space behind the stomach called that is created by the longitudinal rotation of the stomach?

Answer 13

Omental bursa or lesser sac

Question 14

What is the duodenum formed by?

Answer 14

The caudal part of the foregut and the cranial part of the midgut (this means that the duodenum has two different blood supplies)

Question 15

What are the two blood supplies of the duodenum?

Answer 15

Ceolic trunk and superior mesenteric artery

Question 16

All of the duodenum is retroperitoneal except which one part?

Answer 16

The duodenal cap

Question 17

What does the liver bud give rise to?

Answer 17

The gall bladder, Cystic duct and bile duct.

Question 18

In the liver what cells originate from the endoderm

Answer 18

Hepatocyte’s and biliary epithelia

Question 19

In the liver what cells develop from the mesoderm?

Answer 19

Kupffer cells, haematopoietic cells and connective tissue

Question 20

What are the key landmarks of the spleens development?

Answer 20

Mesodermal origin - week 5
Colonised by t-lymphocytes - weeks 15-17
The b-cell precursors arrive and spleen starts it’s lymphoid function

Question 21

Where do the pancreases originate from?

Answer 21

The ventral pancreas bud and the dorsal pancreas bud

Question 22

What happens to the position of the bud as the duodenum rotates?

Answer 22

The ventral bud moves close to the dorsal bud (goes posteriorly)

Question 23

What happens to the pancreas buds after the duodenal rotation?

Answer 23

They join together and form the pancreas, the main pancreatic duct joins with the bile duct and it opens into the major duodenal papilla

Question 24

Classify the mid gut

Answer 24

It extends from the opening of the bile duct into the duodenum up to the proximal 2/3 of the transverse colon

Question 25

What is atresia?

Answer 25

Absence of an opening

Question 26

What is stenosis?

Answer 26

Narrowing of an opening

Question 27

What rotation does the midgut do

Answer 27

90° anti-clockwise

Question 28

What shape does the rotation cause?

Answer 28

A u-shaped primary intestinal tube

Question 29

What axis is the mid gut rotation on?

Answer 29

It is along the superior mesenteric artery (the artery of the midgut)

Question 30

What is the point of the primary intestinal loop attacked to?

Answer 30

The ilium is connected to the yolk sac by the vitelline duct

Question 31

When does the vitelline duct disintegrate?

Answer 31

Up to the 12th-14th week

Question 32

In the 6th week what happens after the loop is formed?

Answer 32

The loop herniates into the umbilical cord, a process called physiological umbilical herniation.

Question 33

When do the intestinal loops move back into the abdominal cavity?

Answer 33

10th week (around)

Question 34

Why does physiological umbilical herniation take place?

Answer 34

In early feotal growth there is not enough room for the intestines to grow because of the huge size of the other organs

Question 35

The primary midgut loop Will elongate and differentiate into?

Answer 35

Part of the duodenum, jejunum, ileum, ascending colon and two-thirds of the transverse colon

Question 36

When does the Cecal bud develop?

Answer 36

Around week 6

Question 37

Where does the appendix grow?

Answer 37

A small ridge on the cecum

Question 38

The position of the appendix can be variable, what are the most common positions?

Answer 38

Sub-cecal or retro-ileal

Question 39

Where will the ascending and descending Part of the colon fuse?

Answer 39

The posterior body wall, becoming retroperitoneal

Question 40

What parts of the mid and hind gut are intraperitoneal?

Answer 40

Appendix, caecum, transverse and sigmoid colons, jejunum and ileum (the small intestine)

Question 41

What is omphalocele?

Answer 41

Failure of retraction of herniated intestinal loop

Question 42

What are the possible remnants of the vitelline duct?

Answer 42

May form fistula, cyst, ligament

Question 43

What often causes stenosis in the gut?

Answer 43

Vascular accidents, possibly from thrombosis, or twisting of bowel - the blood supply to region is compromised and this can result in necrosis of the tissue

Question 44

Hind gut parts of endoderm origin:

Answer 44

Distal 1/3rd transverse colon, descending colon, sigmoid colon, rectum and upper Part of the anal canal

Question 45

Hind gut parts with ectoderm origin:

Answer 45

Lower part of the anal canal and anal orifice

Question 46

What does the Allantois form?

Answer 46

The bladder, urethra and structures like that

Question 47

What two structures does the anal canal derive from?

Answer 47

The cranial Part of the anal canal has endoderm origin The caudal portion forms from the proliferation and invagination of the ectoderm on the external surface of the embryo

Question 48

Is the difference in derivation for the cranial and caudal parts of the anal canal visible?

Answer 48

Yes, the two regions can be seen Asa pectinate line on the inside of the rectum

Question 49

When does the cloacal membrane rupture?

Answer 49

At the end of week 7

Question 50

What is the blood supply of the foregut?

Answer 50

Coeliac artery

Question 51

What is the blood supply of the midgut?

Answer 51

Superior mesenteric artery

Question 52

What is the blood supply of the hind gut?

Answer 52

Inferior mesenteric artery

Question 53

What is special about the duodenums blood supply?

Answer 53

It is supplied by both the coeliac artery and superior mesenteric artery because it has dual origin from foregut and midgut

Question 54

What is special about the blood supply of the anal canal?

Answer 54

The anal canal above the pectinate line is supplied by the inferior mesenteric artery below the pectinate line is supplied by internal pudendal artery, which is a branch of the internal iliac artery

Question 55

What are some developmental anomalies for the hindgut?

Answer 55

Urorectal fistula - poo goes through urethra Rectovaginal fistula - poo goes through vagina Rectoperineal fistula Imperforated anus- poo doesn't get through the anal canal