Exam 2 - Development of the GI Flashcards
What are the contributions of the 3 layers of the trilaminar embryo?
- Endoderm: epithelial lining of the GI tract from pharynx to upper 2/3 of anal canal, epithelium of all organs that form as evaginations from the gut tube ( liver, pancreas, and gallbladder)
- Mesoderm: CT and smooth muscle
- Ectoderm: contributes to epithelium at the ends of the tube ( lower 1/3 of anal canal)
What does the folding of the embryo result in?
What remains on the outside of the embryo?
- incorporation of the endoderm lines yolk sac into the embryo
- The yolk sac and the allantois
What are sections of the gut tube and what do they ultimately end up forming?
- Foregut: buccopharyngeal membrane through the liver bud (includes pharynx)
- midgut: lower 1/2 of the duodenum to 2/3 of the transverse colon.
- Hindgut: lower 1/3 of the transverse colon to cloacal membrane
What are the 2 rotations that the stomach undergo and what are the main results of these rotations?
- 90 degree rotation around the vertical axis till greater curvature is on the left. Vagal trunks go from right and left orientation to anterior and posterior orientation.
- coronal plane rotation: pyloric part moves from inferior to the right side
What does rotation do to the dorsal mesentery?
-The rotating stomach pulls the dorsal mesentery along thereby stretching it and forming the sac.
Where does the duodenum derive from ?
- Caudal end of the foregut derives parts 1 and 2 of duodenum
- Rostral end of midgut derives part 3 and 4
How does the duodenum become “C-shaped”?
- When the stomach rotates in the coronal plane.
What occurs during the 2nd month that can lead to duodenal atresia?
- The duodenum is obliterated but is recanalized shortly thereafter by apoptosis
What accessory organs develop out of the 2nd part of the duodenum?
- liver, gallbladder, and pancreas
What does the liver grow out of?
- ventral mesentery and penetrates the septum transversum
- endoderm –. parenchyma
- mesoderm: hematopoietic and Kupffer cells
What is one of the main functions of the liver?
- hemopoiesis between weeks 8-30
What does the gallbladder develop from?
- from the outgrowth of the ventral side of the bile duct.
What are the 2 parts of the pancreas derived?
- Parenchyma of the pancreas is derived from the dorsal bud and most of the ducts, inferior head, and uncinate process arise from the ventral bud of endodermal outgrowths.
- all the secreting cells arise from endoderm
What structure connects the superior mesenteric artery to the yolk sac?
The vitalline duct
Due to the loss of space in the midgut what occurs around week 6?
- Midgut herniates through the umbilicus and rotates 90 degrees
- As the midgut returns to the abdominal cavity it rotates an additional 180 degrees for a total of 270 degrees
When does the appendix form?
- After the midgut returns to the abdomen.
What are the 2 results of rotation?
- Twisting of mesentery
- placement of viscera within the abdominal cavity
What is the allantosis an outgrowth of?
- is an outgrowth of the hindgut and a portion of the allantois is extraembryonic, the allantoic stalk projects through the umbilical ring and into the umbilical cord
Where does the hindgut terminate?
In the cloaca (an endoderm lined cavity)
What does the urorectal septum serve to divide?
- Divides the cloaca into the urogenital sinus (bladder and urethra) and recto-anal canal
What does the lower end of the anal canal form from?
- Lower end is derived from surface ectoderm.
What is the general areas are the different segments of the rectal canal derived from?
What is the name of the line differentiating the 2 areas?
- superior 2/3 is derived from hindgut, and lower 1/3 derives from the surface ectoderm
- Pectinate line
What is esophageal atresia?
- incomplete separation of the esophagus and trachea- associated with polyhydraminos (can’t swallow the fluid)
Why does a hiatal hernia occur?
Due to a short esophagus
What is achalasia in relation to the esophagus?
- loss of ganglion cells - dilated esophagus with tonically contracted lower esophageal sphincter- dysphagia.
What is the congenital hypertrophic pyloric stenosis?
- thickening of the pylorus that results in obstruction and the stomach becomes distended and associated with projectile vomiting
What does the patient have with vomiting a few hours after birth that contains bile with distention of the epigastrium? What is a key radiological sign with this?
- Duodenal atresia
- “double bubble sign”
What is associated with extrahepatic biliary atresia?
- atresis of the bile ducts - jaundice occurs shortly after birth and stool is “clay-colored” and urine is dark
What is the pathophys of annular pancreas?
- ventral pancreatic bud encircles and constricts the duodenum; males > females
What is an omphalocele covered in?
- Covered in amnion, because the midgut has not returned to the abdomen
What is an umbilical hernia covered in?
- a protruding mass that is covered in subcutaneous tissue.
What is a gastroschisis?
- intestines herniate into umbilical cord after returning to the abdominal cavity; amnion ruptures.
What is Meckel’s Diverticulum and what is the main features of it?
- Meckel’s Diverticulum - persistence of the vitelline duct that results in rule of 2’s:
1) 2% of pop
2) 2’ from iliocecal valve
3) 2” long
4) 2 types of tissue (gastric and pancreas)
5) typically 2 years
6) males> females by 2x
What has occurred when the cecum is on the left side?
- malrotation
What occurs with Hirschsprung’s Disease?
- failure of neural crest cells to migrate to the caudal 1/3 of the large intestine, absence of parasym ganglia
Fistulas involving the cloaca lead to what?
- improper formation of urorectal septum
- Where is the atresia when vomit is not curdled?
- Where is the atresia when the vomit is curdled milk?
- Where is the atresia when there is bile in the vomit?
- in the esophagus
- gastric
- duodenum
