Digestive System Development

Question 1

Somatic mesoderm with the overlying ectoderm is called the ____ and splanchnic mesoderm and endoderm the ____

Answer 1

somatopleure; splanchnopleaure

Question 2

where are the epithelial components of the GI tract, including those associated with the glands derived from?

Answer 2

endodermal germ layer

Question 3

what does the endodermal germ layer generate?

Answer 3

• mucosal epithelium
• mucosal glands
• submucosal glands (parenchyma)

Question 4

where is the connective tissue and muscle derived from

Answer 4

splanchnic mesoderm

Question 5

what does the splanchnic mesoderm give rise to?

Answer 5

• lamina propria
• muscularis mucosa
• submucosal CT and blood vessels
• muscularis externa
• adventitia/serosa

Question 6

what is the neural crest

Answer 6

neurons and nerves of the submucosal and myenteric plexes

Question 7

are there ectodermal derivatives in the digestive system?

Answer 7

yes from the neural crest cells - enteric nerons

Question 8

what type of folding causes the opening of the gut tube to the yolk sac to draw closed forming a pocket toward the head end of the embryo, which will form the foregut and a posterior “intestinal portal” that will form the hindgut

Answer 8

cranio-caudal and lateral folding

Question 9

what remains open to the yolk sac

Answer 9

midgut

Question 10

the origionally wide opening between the gut and yolk sac is reduced to a narrow passage called the

Answer 10

vitelline duct

also called the yolk stalk

Question 11

what are the cranial and caudal ends of the digestive tube are sealed by

Answer 11

buccopharyngeal; cloacal

Question 12

what controls tissue/organ patterning along the craniocaudal (AP) axis?

Answer 12

hox gene expression

Question 13

what programs the hox code

Answer 13

retinoic acid gradient

Question 14

what does the endoderm form

Answer 14

lining/epithelia and secretory elements of the digestive tube and glands (parenchyma)

Question 15

what does the meoderm form

Answer 15

surrounds the tube and forms connective tissue, smooth muscles for peristalis, stroma of liver and pancreas

Question 16

what are endoderm/mesoderm interactions called

Answer 16

induction

Question 17

what is the region of the foregut just caudal to the pharynx that develops two longitudinal ridges called

Answer 17

tracheoesophageal folds

divides tube ventrally into the trachea and dorsally into the esophagus

Question 18

the lumen of the esophagus becomes temporaily ____ around the 5th week of development and recanalizes by aorund the 9th week

Answer 18

occluded

Question 19

esophageal atresia

abnormal closure

Answer 19

• tracheoesophageal ridges deviate too far dorsally causing the upper esophagus to end as a closed tube
• accompanied by tracheosophageal fistula, in which case gut contents can be aspirated into the lunch after birth causing inflammation or infection

Question 20

eosophageal stenosis

Answer 20

occurs when the eosophagus fails to recanalize

Question 21

congenital hiatal hernia

Answer 21

• eosophagus fails to grow adequately in length
• eophagus is too short and pulls the stomach into the esophageal hiatus in the diagraph
• allows other gut contents to herniate up into thoracic cavity

Question 22

the developing stomach attaches to the body walls by

Answer 22

dorsal/ventral mesentery

Question 23

which wall of the stomach grows faster

Answer 23

dorsal wall

Question 24

the doral and ventral mesenteries of the stomach are retained to become the

Answer 24

greater and lesser omenta

Question 25

what forms the pyloric sphincter

Answer 25

proliferation of mesoderm-derived smooth muscle in the caudal end of the stomach

Question 26

pyloric stenosis

Answer 26

* common in dogs and humans, rare in cats and horses * projectile vomiting/poor growth * nerve defect and muscle hypertrophy around pyloric sphincter

Question 27

what are the four chambers of a ruminant stomach

Answer 27

* rumen * reticulum * omasum * abomasum

Question 28

what signals the endoderm to form liver

Answer 28

mesoderm of the septum transversum and developing heart

Question 29

what is derived from the cardiac mesoderm that is necessary and sufficient to induce liver formation

Answer 29

FGFs

Question 30

what are the two stages to form the liver

Answer 30

1. competance (opens up chromatin) and Bmps 2. specification - Fgfs

Question 31

what are the two outgrowths caudal to the forming liver

Answer 31

1. ventral pancreatic bud 2. dorsal pancreatic bud

Question 32

how is the pancreas specified

Answer 32

by interactions with blood vessels and notochord that repress endodermal Shh

Question 33

what happens as liver growth accelerates

Answer 33

the midgut loop cannot be contained in the perioneal cavity and it herniates into the umbilical cord (Physiological Umbilical Hernia)

Question 34

intestinal developnment involves:

Answer 34

looping, rotation and herniation

Question 35

what is gut looping morphogenesis driven by

Answer 35

forces that arise from the relative growth between the gut loop and the anchoring dorsal mesenteric sheet, tissues that grow at different times

Question 36

what is normal in embryo but abnormal in neonate

Answer 36

* physiological umbilical hernia * yolk stalk/meckel's diverticulum (remnant of vitteline duct) * lack of intestinal lumen * cloacal membrane

Question 37

what is white foal lethal syndrome a defect of

Answer 37

neural crest-derived neurons innervating the submucosal and myenteric plexes