Embryology

Question 1

What happens in the weeks in embryology? (general overview)

Answer 1

• Week 3: Gastrulation
  
  • 3 Layers (Endoderm, Mesoderm, Ectoderm)
• Week 4: Folding
  
  • Development of the body cavities
• Week 5-8
  
  • 1. Yolk sac compressed into vitelline duct, is obliterated​
  • 2. Foregut rotation: Stomach forms and rotates
  • 3. Midgut herniation and first midgut rotation
• Week 10
  
  • Moves back into abdominal cavity
  • Second midgut rotation
• Week 20
  
  • ​Gut tube fuses to posterior abdominal wall

Question 2

What rotations happen in embryology?

Answer 2

• Foregut
  
  • •90⁰ clockwise
  • •Creates lesser sac
  • •Accessory organs also grow and rotate to form the adult arrangement
  • •Occurs concurrent to midgut rotation (wk6)
• Midgut (Wk 5 - 12)
  
  • Herniates
  • Rotates 90⁰ anti-clockwise (around SMA)
  • Retracts (into abdomen)
  • Rotates 180⁰ anti-clockwise (around SMA)
  • Then some GIT fuses to the posterior abdominal wall

Question 3

What happens to the vitteline duct?

Answer 3

• Yolk sac lies outside the embryo connected by a vitelline duct (yolk stalk/duct, omphalomesenteric duct) to the midgut with which it forms a continuous connection.
• Degenerates around the time the midgut herniation return to the peritoneal cavity and the anterior body wall closes (week 8).

Question 4

What is Meckel’s Diverticulum?

Answer 4

• Failure of vitelline duct to obliterate
• Results in an diverticulum in the ileum
• Rule of 2’s
  
  • 2% of population
  • 2” in size
  • 2 feet from ileocecal junction
• Majority are asymptomatic

Question 5

What is the result of midgut rotation?

Answer 5

• •Duodenojejunal flexure is just left of the median plane (at L1)
• •Terminal ileum and ileocecal junction is in the right iliac fossa
• •The mesentery has a broad attachment running obliquely in the infracolic compartment

Question 6

What is intestinal malrotation?

Answer 6

• Mesentery of the small bowel is not in the correct location
• There is a much smaller base as the duodenojejenal flexure and ileum are much closer
• The result is that the small intestine is not fixed in its normal position and ‘twisting’ may occur

Question 7

What is midgut volvulus?

Answer 7

• As it may ‘twist’ around the SMA and SMV and cause ischaemia (serious)
• It is not only a congenital anomaly. Though rarer, it may occur in adults and typically sigmoid colon
• If your patient had chronic constipation issues, the distended loops of sigmoid colon may twist around each other to form a sigmoidal volvulus

Question 8

What is Intussusception?

Answer 8

• A segment of the bowel invaginates the portion just distal to it
• Typically at the ileocecal junction
• This results in luminal obstruction
• Bull’s Eye