Devo Flashcards
What are the precursors of the GI tract?
Endoderm–epithelial components of gut
Splanchnic Mesoderm–muscle, connective tissue, and other layers of the wall of the gut
Coelomic epithelium covering the splanchnic mesoderm
What does the foregut endoderm give rise to?
The epithelium of the esophagus, stomach, proximal duodenum, thyroid, lung, liver and pancreas
What does the midgut endoderm give rise to?
The epithelium of the distal duodenum, jejunum, ileum, cecum, appendix and colon
What does the hindgut endoderm give rise to?
The remaining part of the transverse colon, the descending and sigmoid colon, the rectum, and the superior part of the anal canal
What does folding of the embryo in the transverse plane create?
The primitive gut tube from the endoderm
What does folding of the embryo in the sagittal plane create?
Three subdivisions of the primitive gut tube – foregut, midgut and hindgut
At about 7 weeks how does the 90 degree rotation change the position of the stomach?
The greater curvature (which arises from the embryonic dorsal side) now faces the left side of the body
The lesser curvature (which arose from the embryonic ventral side) faces the right side of the body
What nerves innervated the anterior and posterior walls of the mature stomach?
Anterior wall – left vagus nerve
Posterior wall – right vagus nerve
What is the space posterior to the stomach called?
The lesser sac or mental bursa
What is the space anterior and inferior to the stomach called?
The greater sac
Which ventral branch of the aorta is associated with the foregut, midgut and hindgut respectively?
Foregut: celiac trunk
Midgut: superior mesenteric
Hindgut: inferior mesenteric
Describe the physiological umbilical herniation.
Forms by week 6 when midgut loop herniates through the umbilicus into the umbilical cord
What do the midgut loop cranial and caudal limbs become??
The cranial limb forms the primordial jejunum and ileum
The caudal limb develops the cecal bud which ultimately forms the cecum
When is the body cavity large enough for the midgut to retract into it?
Around week 10
After retraction into the body cavity, where are the cranial limb and caudal limbs localized?
Cranial limb on the left side of the body
Caudal limb on the right side of the body
What is the cloaca?
The expanded terminal region of the hindgut
The dorsal side produces the rectum and part of the anal canal
The ventral side produces the urogenital sinus
What develops into the anal canal?
The superior part develops form the handgun
The inferior region develops from the proctodeum (ectodermally-derived)
What gives rise to the liver, gallbladder and biliary duct system?
The outgrowth of the ventral foregut endoderm
What are the three distinct phases of liver bud formation?
- Foregut endoderm composed of polarized columnar epithelial cells protrudes into the surrounding septum transversum mesenchyme
- The simple columnar epithelium transforms to a pseudostratified epithelium encased in basement membrane.
- The basement membrane is degraded and bipotential hepatoblasts delaminate and migrate into the septum transverse mesenchyme – have the potential to differentiate into hepatocytes, epithelial cells of the liver parenchyma or into cholangiocytes (epithelial cells of the biliary system)
What growth factors help the primordial liver bud along its development?
FGFs and BMPs secreted from heart and the septum transversum mesenchyme
What is the key site of hematopoiesis in the fetus?
The liver!!
What gives rise to the gallbladder?
A small caudal region of the liver bud
The stalk of the bud forms the cystic duct
What gives rise to the bile duct?
The stalk connecting the hepatic and cystic ducts to the duodenum
How does the pancreas develop?
As two buds emanating from the oral and ventral foregut endoderm – The dorsal pancreatic bud and the ventral pancreatic bud
What growth factors are involved in the development of the dorsal pancreatic bud?
The notochord secretes FGF2 and activin to inhibit the growth factor sonic hedgehog and promote pancreatic development instead of intestinal development
Duodenal atresia or duodenal stenosis
Failure to reanalyze or incomplete recanalization of the duodenum –> leads to vomiting
Polyhydramnios occurs with duodenal atresia b/c the blockage prevents proper intestinal absorption of swallowed amniotic fluid
Extrahepatic biliary atresia
Serious anomaly
Commonly caused by obliteration of the bile ducts (85%)
Jaundice soon after birth and stools are echoic (clay colored)
Fatal without liver transplant
Gastroschisis
Defect lateral to the medial plane of the anterior abdominal wall
Abdominal viscera is extruded through eh wall without involving the umbilical cord
Usually occurs on the right side lateral to the umbilicus
Is NOT a hernia because it is not covered in a sac – it is an evisceration
Omphalocele
Herniation of abdominal contents into the proximal umbilicus
Failure of intestine to return to the abdomen during development causes omphalocele
Why do congenital anomalies of the small intestine commonly occur?
Because of defects in gut rotation including nonrotation or malrotation
Meckel divertitculum
Out pocketing of ileum, common anomaly of GI tract – remnant of the omphaloenteric duct
Can become inflammed and mimic appendicitis
Hirschsprung disease
Aganglionosis of the colon – presents as megacolon because the affected tissue (which lacks ganglion cells) fails to relax –> prevents movement of bowel contents
