Digestive System Development

Question 1

Where is the primitive gut divided? What is it divided to? What is it connected to?

Answer 1

Divided into foregut beginning at the buccopharyngeal (oropharyngeal) membrane, midgut, connected to yolk sac by vitelline duct, and hindgut that ends at the clocal membrane

Question 2

The primitive gut is developed from two things. What is the difference? What does it form?

Answer 2

Develops from endoderm — forms epithelial lining of gut, gives rise to parenchyma of glands (e.g., liver, pancreas)

Develops from splanchnic mesoderm — forms smooth muscle, connective tissue, and visceral peritoneum of the gut wall

Question 3

Where is the pharyngeal gut?

Where is the foregut?

Answer 3

The cranial part of foregut; it extends from buccopharyngeal (oropharyngeal) membrane to respiratory diverticulum (lung bud)

Foregut — between respiratory diverticulum and lung bud

Question 4

What is the dorsal mesentery? What is it divided into?

Answer 4

It suspends the foregut, midgut, and hindgut from the posterior abdominal wall

It is divided into the dorsal mesogastrium, dorsal mesoduodenum, and ventral mesentery

Question 5

Where is the dorsal mesogastrium located? Dorsal mesoduodenum? Ventral mesentery?

Answer 5

Dorsal mesogastrium (greater omentum) in stomach region

Dorsal mesoduodenum, mesentery proper (in regions of jejunum and ileum), and the dorsal mesocolon (in region of colon)

Ventral mesentery — present only in region of abdominal portion of esophagus, stomach, and upper duodenum

Question 6

The growth of what divides the ventral mesentery? Into what?

Answer 6

Growth of liver into septum transversum divides ventral mesentery into the falciform ligament and lesser omentum

Question 7

Where is the foregut located during development?

Answer 7

Cranially, borders pharyngeal gut at respiratory diverticulum (lung bud)

Question 8

What is the lining found in the foregut and what forms them?

Answer 8

It has an epithelial lining formed by endoderm

Muscular coat formed by surrounding formed by the surrounding splanchnic mesoderm

Question 9

What does the foregut give rise to?

Answer 9

Esophagus, stomach, first part, and half of second part of duodenum, liver & gallbladder & pancreas

Question 10

Where are the pharyngeal arches located? What innervates it?

Answer 10

It is located in the upper part of the esophagus. They are innervated by the vagus nerve

Question 11

What is in the lower part of the esophagus? What innervates it?

Answer 11

It has smooth muscles from the splanchnic mesoderm and innervated by parasympathetic fibers of the esophageal plexus (vagus nerve)

Question 12

What is esophageal atresia?

What causes it?

what can it result to?

Answer 12

It causes the esophagus to end in a blind-ended pouch rather than connecting normally to the stomach

It is caused by a deviation to the trachea-esophageal septum

It can lead to polyhydramnios (excess in amniotic fluid)

Question 13

What is tracheoesophageal fistula?

Answer 13

It is the abnormal connection (fistula) between the esophagus and the trachea

Question 14

What is the esophageal stenosis?

Answer 14

It is esophageal narrowing. It is due to the incomplete recanalization following the epithelial proliferation phase

Question 15

Describe the development of the stomach

Answer 15

Develops as a fusiform swelling of the foregut. Rotates 90° clockwise about a longitudinal axis so that its original left side (L) faces anteriorly, left vagus nerve forms most of the anterior vagal trunk, and right vagus forms most of posterior vagal trunk

Stomach rotates again 90° about anteroposterior axis so that lesser curvature faces upward right and greater curvature faces downward left

Question 16

What happens to the dorsal mesogastrium due to stomach rotation?

Answer 16

Dorsal mesogastrium is pulled to left and elongates creating omental bursa (leser peritonieal sac) behind stomach and lesser omentum

Question 17

What is the spleen derived from?

Answer 17

Develops by “budding process” from mesoderm within dorsal mesogastrium dividing it into gastroplenic (gastrolienal) and splenorenal (lienorenal) ligaments

Tail of pancreas enters the splenorenal ligament

Question 18

What is the duodenum derived from?

Answer 18

First and second part proximal to the development of the liver bud comes from the caudal foregut

Third and fourth part develop from the midgut

Question 19

What eventually happens to the dorsal mesoduodenum?

Answer 19

It disappears except at the first part of the duodenum (duodenal cap/ampulla). It becomes secondarily retroperitoneal

Question 20

What causes duodenal stenosis or atresia?

Answer 20

It results from the incomplete recanalization of the duodenum

Duoedenal atresia has a characteristic “double bubble sign” on ultrasound scans. Polyhydramnios is present. Bile-stained vomiting occurs shortly after birth

Question 21

Describe the development of liver and gallbladder

Answer 21

It develops by budding process (endodermal proliferation) forming hepatic diverticulum (liver bud), from the middle of the second part of the duodenum where it remains connected (common bile duct)

Question 22

What happens to hepatic buds?

Answer 22

They are an extension of the embryonic foregut endoderm that gives rise to the liver. They proliferate repeatedly into hepatic cords (glandular parenchyma) through septum transverse, invading vitalize veins, forming hepatic sinusoids

Question 23

What forms the cystic duct and gallbladder?

Answer 23

They form from the small ventral outgrowth from the future bile duct in the liver bud

Question 24

What is the liver’s function during embryonic development?

Answer 24

It is important for hematopoiesis from 6 weeks to 6 months of gestation. It is colonized mainly by hematopoietic stem cells that arise near the aorta in the aorta-gonad-mesonephros region

It secretes bile at approximately 12 weeks, excess bile is stored and concentrated in the gallbladder

Question 25

What forms the pancreas?

Answer 25

It is formed by a dorsal pancreatic bud in the dorsal mesoduodenum and a ventral pancreatic bud that develops close to the bile duct

With duodenenal rotation to the right, ventral pancreatic bud moves dorsally to fuse with the dorsal pancreatic bud. Ventral bud forms uncinate process and inferior part of the head and the dorsal bud forms the rest of the gland

Question 26

Describe duodenal rotation

Answer 26

It rotates to the right, forming a C-shaped structure around the head of the pancreas

Question 27

Where does the pancreatic duct (of Wirsung) develop from?

Where does the accessory pancreatic duct (of Santorini) develop from?

Answer 27

It develops from the distal part of the dorsal pancreatic duct and the entire ventral pancreatic duct

It develops from the proximal part of the dorsal pancreatic duct

Question 28

What causes extra hepatic biliary atresia?

Answer 28

It occurs when hepatic or bile duct fails to recanalize after their budding

Question 29

What occurs with an annular pancreas?

Answer 29

Two components of ventral pancreatic bud migrate in opposite directions to encircle the duodenum with possible duodenal obstruction

Question 30

What forms from the cephalic limb of the midgut?

Answer 30

This forms the distal duodenum, jejunum, and part ileum

Question 31

What forms from the caudal limb of the midgut?

Answer 31

It forms the lower ileum, cecum, appendix, ascending colon, and proximal 2/3 of the transverse colon

Question 32

Explain physiological umbilical herniation

Answer 32

The liver grows much faster than the abdominal cavity to become too small to accommodate intestines forcing intestinal loops to enter the umbilical cord

Question 33

Explain the development of the intestine

Answer 33

Primary intestinal loop rotates around the SMA, a total of 270° counterclockwise (viewed from the front

Cecum then buds form the colon in the right upper quadrant and descends to the right lower quadrant

Question 34

What happens to the mesentery of the jejunum and ileum during the fixation of intestines?

Answer 34

They are placed in a new line of attachment, from the duodenojejunal to the ileocecal junction

Question 35

What happens if the mesentery of the lower part of the ascending colon fails to fuse with posterior body wall?

Answer 35

The cecum may become twisted on it in cecal volvulus

Question 36

What does the cloaca dive into? What divides it?

Answer 36

It divides into the anterior urogenital sinus and posterior anorectal canal by the growth of the mesodermal urorectal septum

Question 37

Where does the cranial part (above pectinate line) of the anal canal develop from?

Answer 37

It develops from the cloacal endoderm

Question 38

Were does the caudal part of the anal canal (below the pectinate line) develop from?

Answer 38

It develops from ectoderm

Question 39

What causes imperforate anus?

Answer 39

It is due to a failure of recanalization of the lower portion of the anal canal following epithelial proliferation

Question 40

How does urorectal or rectovaginal fistula develop?

Answer 40

When the opening of the hindgut shifts anteriorly because the urorectal septum does not extend far enough caudally

Question 41

How does congenital megacolon (Hirschsprung’s disease) develop?

Answer 41

Autonomic (parasympathetic) ganglia are absent from a segment of the intestine