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What happens at the ends of the gut tube prior to the 4th week? (2)
It is closed at both ends by the:
  • oropharyngeal membrane
  • cloacal membrane 
The epithelium and parenchyma (liver, spleen) are derived from what germ layer?
Endoderm
The muscular layers of the GI tract (lamina propria, muscularis mucosae, submucosa, muscularis externa, adventitia and/or serosa) and other connective tissue are derived from what germ layer?
Splanchnic mesoderm
Name the derivatives of the gut relevant to GI block (5)
  • Esphagus
  • Stomach
  • Duodenum (proximal)
  • Liver and biliary appartus (gallbladder, bile duct)
  • Pancreas
What divides the esophagus and trachea during development?
Esophagotracheal septum
  • Esophageal atresia is most often caused by what?
  • What is the common clinical presentation (1)?
  • Abnormal division of tracheoesophageal septum
  • Presentation:
    -Polyhydramnious (excessive amniotic fluid because fetus cannot swallow)
  • The upper 2/3 of the esophagus and the lower 1/3 of the esophagus are what type of muscle?
  • What innervates
  • Upper 2/3: Striated (vagus)
  • Lower 1/3: Smooth (vagus via Celiac plexus)
As the stomach develops, there is a fusiform enlargement of the caudal part.
  • In what direction and how many degrees does the stomach rotate?
  • It rotates about which axis?
The stomach rotates 90 degrees clockwise, such that the ventral surface (lesser curvature) moves to the right and the dorsal surface (greater curvature) moves to the left.
  • It rotates about the longitudinal axis 
About the dorsal mesentry:
  • What is it called?
  • It attaches the stomach to what?
  • Called dorsal mesogastrium
  • Attaches stomach to posterior body wall
About the ventral mesentry:
  • What is it called?
  • It attaches the stomach to what?
  • What organ develops within it that divides it into what 2 things?
  • Called ventral mesogastrium
  • Attaches stomach to anterior body wall
  • Liver develops within to divide it into the falsiform ligament and lesser omentum
  • The falsiform ligament contains what structure?
  • What does this structure turn into in the adult? 
  • Falsiform ligament contains the umbilical vein
  • After birth it becomes the round ligament of the liver
How many layers do the mesogastria have?
They are double-layered
What is the omental bursa?
Lesser peritoneal sac
  • Created by rotation of stomach, when dorsal mesogastrium went left and ventral mesogastrium went right
What is the epiploic foramen of Winslow (also known as the omental foramen)?
The only opening into the lesser sac
  • Connects the lesser peritoneal sac to the rest of the peritoneal cavity (greater sac)
  • What is congenital hypertrophic pyloric stenosis?
  • What is the primary symptom associated with this?
  • When the pylorus is hypertrophic
  • Leads to projective vomiting (also polyhydramnios) 
Does the duodenum develop from the foregut or midgut?
Hah, trick question!
  • It develops from both foregut and midgut and therefore gets blood from both the celiac and superior mesenteric arteries (in addition it also has dual innervation)
What is the division between the foregut and midgut?
Just distal to the major duodenal papilla
Which of the following is the duodenum?
  • Intraperitoneal
  • Primary retroperitoneal
  • Secondary retroperitoneal
Secondary retroperitoneal
  • Because it develops within mesentery that is later lost by fusing with the abdominal wall 
Name the 2 steps of development of the duodenum?
  • 1. Proliferation of epithelial cells obliterating the lumen
  • 2. Recanalization and reopening of lumen
Name 2 congenital malformations of the duodenum and describe
  • Duodenal stenosis:
    -Partial occlusion of the duodenal lumen, due to incomplete recanalization
  • Duodenal atresia:
    -Total occlusion of duodenal lumen, due to incomplete recanalization
What are symptoms of duodenal atresia (2)?
Similar to congenital hypertrophic pyloric stenosis, because the pathway to intestines is blocked:
  • Vomiting (food gets stuck and comes back up)
  • Polyhydramnios (amniotic fluid can't reach GI tract for absorption)
  • Where does the hepatic diverticulum arise?
  • What structures does it form?  (3)
  • Hepatic diverticulum is a ventral outgrowth from the caudal part of the foregut
  • Gives rise to the liver, gallbladder and  biliary system
The following parts of the liver bud become which structures? (3)
  • Cranial
  • Caudal
  • Stalk 
  • Cranial part: Grows superiorly to meet septum transversum and form parenchyma of liver
     
  • Caudal part: Becomes gall bladder
     
  • Stalk: Forms bile ducts
What is another name for the liver bud?
Hepatic diverticulum
What is extrahepatic biliary atresia?
  • What is the cause of biliary atresia?
  • What is a possible consequence of biliary atresia?
The bile duct is formed from the stalk of the liver bud by occlusion and recanalization
  • Biliary atresia is due to failure of recanalization
  • Can result in duplication of gallbladder 
  • The pancreas develops from what 2 structures?
  • What parts of the pancreas develop from which structure? 
  • Ventral bud (head)
  • Dorsal bud (rest of pancreas)
What happens with the ventral bud and dorsal bud to make the pancreas?
The ventral pancreatic bud must grow around the duodenum where it merges with the dorsal pancreatic bud
  • Main pancreatic bud is made from?
  • Accessory pancreatic bud is made from? 
  • Main pancreatic duct: Distal dorsal duct and ventral duct
  • Accessory pancreatic duct: Proximal dorsal
What are 2 problems that can occur resulting in pancreatic malformation?
  • Accessory pancreatic tissue in wrong place (stomach, duodenum or ileal diverticulum)
  • Annular pancreas (if the ventral pancreatic duct wraps around both sides of the duodenum making a loop and "tying off" the duodenum)
  • What cells does the spleen develop from?
  • The spleen grows from what structures?
  • Spleen develops from mesenchymal cells between the layers of the dorsal mesogastrium
  • Develops from lobules, which appears as indentations once the spleen fuses
Name a primary retroperitoneal organ?
Kidney

(See, I thought you'd pick the kidney!)
Go through digestive tract from abdominal esophagus to anus and say whether the structure is intraperitoneal or retroperitoneal.

  • Abdominal Esophagus → R
  • Stomach → I
  • Duodenum → Mainly R
  • Jejunum, Ileum, Appendix → I
  • Cecum → R
  • Ascending → R
  • Transverse → I
  • Descending → R
  • Sigmoid → I
  • Rectum/Anal → R
What are the derivatives of the midgut? (5)
  • Small intestine (including most of duodenum)
  • Cecum
  • Vermiform appendix
  • Ascending colon
  • Proximal 2/3 of transverse colon
  • Which artery supplies midgut?
  • How is the midgut suspended in the abdomen? 
  • Superior mesenteric artery
  • Midgut is suspended by elongated mesentery
Describe the development of the midgut loop (2)
  • Midgut loop (ventral U-shaped loop) forms with two limbs (cranial and caudal)
  • Midgut loops projects proximally into umbilical cord because not enough room in abdomen for rapidly growing midgut (ie. physiological umbilical hernia)
  • Describe the rotations of the midgut loop during development (2)
  • Rotations occur around which axis
  • There is one 90-degree rotation during protrusion into the abdomen
  • There is a 180-degree rotation when the midgut loop returns to the abdomen
  • Rotation occurs around the axis of the superior mesenteric artery 
  • When do intestines return to abdomen?
  • Which part of intestines returns to abdomen first
  • 10th week
  • Small intestines return before the large intestine
Rotation of the stomach and duodenum brings the duodenum and pancreas to the right side of the abdominal cavity. They are pressed onto the posterior abdominal wall by the colon.
  • Then what happens?
  • What other parts of the GI tract does this happen to? 
  • The layers of peritoneum fuse and subsequently disappear
  • The pancreas and most of the duodenum become retroperitoneal as a result
  • This also happens to the ascending and descending colon
What forms from the cecal diverticulum, which appears as a swelling in the midgut? (3)
  • Ascending colon
  • Cecum
  • Appendix
What is a major abnormality of the midgut involving the umbilicus?
Congenital omphalocele
  • Persistence of the herniation of the abdominal contents into the proximal part of the umbilical cord
  • Imagine an umbilical cord sort of filled with intestines and other abdominal contents 
  • What is gastroschisis?
  • What happens as a result? 
  • Malformation of the anterior abdominal wall (ie. incomplete closure of lateral folds)
  • Abdominal viscera protrude into amniotic cavity
  • What is an umbilical hernia?
  • What is the cause?
  • Hernia around belly button
  • When intestines herniate a second time because umbilicus not properly closed (remember: first time was normal or "physiological")
Most anormalities of the midgut are caused by what?
Malrotation of gut
  • What is non-rotation of the gut?
  • What causes it?
  • Small intestines on the right and colon on the left
  • Happens because midgut loop does not rotate on re-entry
  • What is reversed rotation of the gut?
  • What can happen as a result?
Midgut loop rotates in a clockwise rather than counterclockwise direction.
  • Duodenum lies anterior to superior mesentery artery (SMA) and transverse colon lies posterior to SMA
  • Transverse colon may be obstructed by pressure from the SMA

Summary: Intestines rotate the wrong way, then the high pressure of SM artery presses against the transverse colon, blocking it.
  • How does subhepatic cecum and appendix occur?
  • What is the consequence? 
Cecum adheres to inferior liver and when it returns to abdomen after herniation, the cecum remains in its fetal position
  • What is Meckel's diverticulum (also known as Ileal diverticulum)?
  • What is the clinical significance?
  • What may be secreted
  • Meckel's diverticulum is the proximal portion of the yolk stalk, that can remain
  • Clnical significance is inflammation mimicking appendicitis
  • The wall of diverticulum may contain gastric cells that can secrete acid and cause ulcers and bleed
  • What is an umbilicoileal fistula (also known as an omphaloenteric fistula)?
  • How does it occur?
  • Connection between intestines and belly button (I call this a "smelly button")
  • Results from persistence of the entire intra-abdominal portion of the yolk stalk
Duplication of the intestine is a congenital abnormality.
  • How does it occur?
There is a solid stage of intestine development, and then vacuoles develop to form the lumen. Normal recanalization can fail if the vacuoles don't fuse properly, leading to the creation of two lumens (tubular duplication).
What are the derivates of the hindgut? (7)
  • Left 1/3 of the transverse colon
  • Descending colon
  • Sigmoid colon
  • Rectum
  • Superior part of anal canal
  • Epithelium of urinary bladder
  • Most of urethra
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