Development of the Digestive System Flashcards
When does lateral and caudal folding occur?
Week 4
How does body folding play a role in forming the primordial gut?
During folding, endoderm from the dorsal portion of the yolksac is incorporated into the embryo as the innermost lining of the gut tube (epithelial lining and glands of the GI tract)
Vitelline duct
Connection of the midgut to the yolksac
What are the boundaries of the Foregut?
Rostal - Oropharyngeal membrane
Caudal - Rostral edge of the Vitelline duct
What is the arterial supply for the foregut?
Celiac trunk
What are the boundaries for the midgut?
Rostral - Rostral edge of Vitelline duct
Caudal - Caudal edge of Vitelline duct
What is the arterial supply for the mdigut
Superior Mesenteric Artery
What are the boundaries for the hindgut?
Rostral - Caudal edge of the Vitelline duct
Caudal - Cloacal membrane
What is the arterial supply for the hundgut?
Inferior Mesenteric artery
What does the endoderm contribute to the GI tract?
Epithelial lining
Glands of the GI tract
What does the Mesoderm (splanchnic) contribute to the GI tract?
Smooth muscles and connective tissue of the GI tract (includes peritoneum and mesenteries)
What does the Neural Crest (ectoderm) contribute to the GI tract?
Enteric nervous system
What is the result for nerual crest cells failing to migrate to the GI tract?
Hirschsprung’s Disease
Hirschsprung’s Disease
Aganglionic portion severly constricts
Bowels distend proximal to constriction, causing no peristalsis. This leads to sever constipation and failure to thrive
Peritoneum
Serous membrane lining the abdominal cavity (parietal) and organs (visceral)
Mesentary
Double layer of peritoneum that suspends organs from the body wall
Connective tissue, vessels, nerves, and lymphatics are located here
What does the Greater Omentum develop from?
From the dorsal mesogastirum
What does the Lesser Omentum develop from?
From the ventral mesogastrium
What does the Falciform ligament develop from?
From the ventral mesogastrium
How does the lower respiratory tract arise?
At week 4, a respiratory diverticulum appears on the ventral side of the forgeut (becomes the trachea, lungs, and respiratory tree)
It separates from the esophagus by pinching of membrane on lateral intersection of diverticulum/esophagus
What is a tracheoesophageal fistula
A hole form trachea to esophagus
If tracheoesophageal ridges fail to fuse together to form a septum
Esophageal atresia
Localized absence of esophageal lumen due to poor recanalization of epithelial plug
Superior esophagus becomes a dead-end pouch, leading to polyhydraminos
Polyhydraminos
Excess of amniotic fluid in amniotic cavity
How does the dorsal mesogastrium change with growth and rotation of the stomach and duodenum?
The dorsal mesogastrium is carried to the patient’s left as the stomach rotates
Omental bursa
Recess between the stomach and posterior abdominal wall
Right vagus nerve innervation of the stomach
Dorsal stomach (greater curvature)
Left vagus nerve innervation fo the stomach
Ventral stomach (lesser curvature)
Pyloric stenosis
A birth defect where the pylorus is narrowed by excessive smooth muscle constriction - leading to the inability to digest, causing hardcore projectile vomiting
How would you fix a pyloric stenosis
Surgical intervention 2-5 weeks after birth to mechanically open the pylorus
How would vomit of pyloric stenosis compare to that of an infant with duodenal atresia?
Bile duct is located in the duodenum, so duodenal atresia vomitus contains bile causing it to look green-ish
Development of Liver, gallbladder, and bile ducts
Hepatic diverticulum of distal foregut
Emerges ventrally from endoderm in week 4, grows superiorly toward septum transversarium
Development of Pancreas
Forms from the dorsal and ventral pancreatic buds
Dorsal bud connects to duodenum directly
Ventral bud is connected to the bile duct
As the duodenum rotates, the ventral bud swings around clockwise under the dorsal bud, then fuse
How does an annular pancreas develop?
The ventral bud can sometimes be 2 lobes instead of 1
Multiple ventral lobes can wra around in separate directions and end up hugging the dupdenum and obstructing it
One lobe goes clockwise, the other counter clockwise
What structure serves as the aaxis of rotation for the midgut?
Superior Mesenteric Artery
What is the normal rotation of the midgut?
2 rotations:
1st (week 6): 90 degrees CCW
2nd (week 10): 180 degrees CCW
(net of 90 degrees CW)
What does normal rotation of the midgut lead to?
Ascending and descending colons being secondarily peritoneal
What is nonrotation of the midgut?
The first rotation occurs, but the second does not
The colon is on the left side only
What is reverse rotation of the midgut?
The first rotation occurs normally, but the second rotation occurs clockwise
Duodenum is now ventral to transverse colon
What are the 2 types of umbilical herniation?
Omphalocele
Gastroschisis
When does an omphalocele occur?
Week 10
When does a Gastrochisis occur?
Week 4
Describe an Omphalocoele
Heniation of GI organs
Medially placed herniated umbilicus
Outpouched peritoneum
Describe a Gastrochisis
Herniation of GI organs
Laterally placed herniated abdominal wall, no overlying tissue
Which umbilical herniation is larger?
Omphalocoele
What is recanilization in normal gut formation?
Intestines become occluded by epithelial cells (epithelial plug) at week 8
The plug recanalizes via vacuole formation by the end of week 8
What are vacuoles role in the recanalization of the epithelial plug?
The vacuoles connect to make a hollow, yet rough endoderm
Stenosis
Insufficient recanalization of epilithelial plug
Meckel’s Diverticulum
Remnant of Vitelline duct
An outpouching of the ileum 40-60 cm from ileocecal juncation
What are some complications of Meckel’s Diverticulum?
May contain pancreatic tissue or gastric mucosa that secretes acid, causing bleeding and ulcers
Urorectal Septum
Physical barrier between primitive urogenital sinus and hindgut
Grows inferiorly toward cloacal membrane, dividing it into urogenital and anal membranes, and partitioning the urogenital sinus and anorectal canal
