Development Of The GI Tract

Question 1

When does the GI tract develop in vivo?

Answer 1

3-12 weeks

Question 2

When are the primary germ layers formed?

Answer 2

Gastrulation

Question 3

What is the embryo made of at the beginning of the third week?

Answer 3

Epiblasts and hypoblasts

Question 4

What are the steps in gastrulation?

Answer 4

• epiblast cells in the midline begin to ingress, starting from the caudal end
• ingressing cells differentiate into the mesoderm
• epiblast gives rise to the ectoderm
• hypoblast and epiblast gives rise to the endoderm

Question 5

What are the ingressing epiblast cells visible as?

Answer 5

The primitive streak

Question 6

What types of cells do the ingressing cells differentiate into?

Answer 6

Surrounding muscles, connective tissue, mesenteries and blood vessels

Question 7

What does the epiblast form?

Answer 7

Innervation of the gut (enteric nervous system)

Question 8

What does the hypoblast form?

Answer 8

Epithelium of the gut tubes and glands

Question 9

How many primary layers does gastrulation generate?

Answer 9

3

Question 10

How is the gut tube formed initially?

Answer 10

Folding of sheets of cells in two directions

Question 11

What are the two directions that the sheets of cells are folding in?

Answer 11

Along the midline (cranial-caudal axis)

Towards the yolk sac at the cranial and caudal ends

Question 12

What part of the nervous system is important in gut motility?

Answer 12

Splanchnic nervous system

Question 13

What does Vitelline mean?

Answer 13

Relating to, or associated with the yolk of an egg

Question 14

How many arterial branches are there to the thoracic oesophagus?

Answer 14

5

Question 15

Where does the sympathetic ganglia develop next to?

Answer 15

Major branches of the aorta

Question 16

What nerve innervates the foregut?

Answer 16

Coeliac ganglion

Question 17

What nerve innervates the midgut?

Answer 17

Superior mesenteric ganglion

Question 18

What nerve innervates the hindgut?

Answer 18

Inferior mesenteric ganglion

Question 19

How does the stomach arise?

Answer 19

Expansion and rotation

Question 20

When does stomach development start?

Answer 20

Week 4

Question 21

What happens to the stomach in week 4?

Answer 21

Tube dilates forming an enlarged lumen

Question 22

What are the steps in stomach development?

Answer 22

90 deg turn about the cranial caudal axis -> dorsal border grows more rapidly than the ventral

Question 23

What fixes the mature gut in place?

Answer 23

Fusion of the mesenteries with the posterior abdominal wall

Question 24

How is the lesser sac formed?

Answer 24

As the stomach rotates, the dorsal mesogastrium is drawn with it and encloses a space (the lesser sac)

Question 25

What is a pyloric stenosis?

Answer 25

Gastric outlet obstruction caused by smooth muscle hypertrophy

Question 26

What are the symptoms of pyloric stenosis?

Answer 26

Projectile vomiting shortly after feeding

Question 27

What is the inducing signal for the formation of the liver?

Answer 27

Heart to ventral gut endoderm

Question 28

How does liver formation start?

Answer 28

Hepatic diverticulum grows into the mesenchyme of septum transversum

Question 29

What happens when the liver exceeds the size of the septum transversum?

Answer 29

Expands into the ventral mesentery

Question 30

What does the remaining ventral mesentery give rise to?

Answer 30

The falciform ligament between the liver and body wall Lesser omentum between liver and stomach

Question 31

Where does pancreas formation originate from?

Answer 31

2 pancreas buds

Question 32

What are the two pancreas buds called and where are they found?

Answer 32

Dorsal from the duodenal endoderm | Ventral from the hepatic diverticulum

Question 33

What is the dorsal pancreatic bud induced by?

Answer 33

Notochord

Question 34

What is the ventral pancreatic bud induced by?

Answer 34

Hepatic mesoderm

Question 35

What happens to the two pancreas buds as the duodenum rotates?

Answer 35

Ventral and dorsal buds meet and fuse

Question 36

What does bifid mean?

Answer 36

Bi-lobed

Question 37

What happens if the ventral bud is bifid and one rotates anteriorly?

Answer 37

An annular pancreas forms, which can obstruct the duodenum

Question 38

What mesentery is attached to the intestine?

Answer 38

Dorsal mesentery

Question 39

What causes the folding of the gut?

Answer 39

The gut grows faster than the mesentery

Question 40

What are the first 3 steps in intestine development?

Answer 40

- Intestines rotate around the superior mesenteric artery - herniate into umbilical stalk at 6/7 weeks - intestines return to body at 10 weeks?

Question 41

Why do the intestines herniate into the umbilical stalk?

Answer 41

Abdomen is too small to accommodate

Question 42

What is an umbilical hernia?

Answer 42

When the rectus abdominis (muscle) fails to fuse around the umbilicus after the intestines have retuned to the abdomen. Skin forms over the top

Question 43

What is omphalocele?

Answer 43

Failure of intestinal loops to return into abdomen - hernia covered in amnion

Question 44

What is the cause of omphalocele?

Answer 44

Unknown, but related to maternal obesity, alcohol/tobacco, antidepressant use

Question 45

What is gastrochisis?

Answer 45

Failure of the ventral body wall to fuse (no covering on the GI tract)

Question 46

What is gastroschisis associated with?

Answer 46

Young maternal age, low maternal BMI and recreational drug use

Question 47

If the yolk duct persists, where is it attached?

Answer 47

Ileum, near the ileocecal junction- apex of midgut loop (2ft from ileocecal junction)

Question 48

What are the symptoms of meckels diverticulum?

Answer 48

Usually asymptomatic- can get inflamed (indistinguishable from acute appendicitis)

Question 49

What is meckels diverticulum?

Answer 49

Persistence of the yolk duct

Question 50

What happens if the meckels diverticulum contains ectopic gastric cells?

Answer 50

Ulceration and lower GI bleeding

Question 51

What happens if the meckels diverticulum is connected to the umbilicus by a ligament?

Answer 51

- gut rotation can cause a volvulus | - umbilical fistula

Question 52

What is a volvulus?

Answer 52

Strangulation- like a ballooning effect

Question 53

What’s an umbilical fistula?

Answer 53

Connection from one epithelial surface to another- means the contents can leak out

Question 54

What are the symptoms of Hirschsprung’s disease?

Answer 54

Dilation of sections of the the colon, with lack of tone and peristalsis

Question 55

What is hirschprungs disease caused by?

Answer 55

Lack of neural crest cells

Question 56

What are neural crest cells?

Answer 56

Move through the embryo to give rise to the enteric ganglia

Question 57

Where do the occipitocervical (vagal) region populate?

Answer 57

Whole gut

Question 58

Where do neural crest cells from the sacral region populate?

Answer 58

Distal gut

Question 59

What is the cloaca?

Answer 59

Transient common end of the digestive and urogenital systems including the base of the urogenital sinus

Question 60

What is the cloaca split by (and when in development)?

Answer 60

Urorectal septum at 7-8 weeks