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
