1 - Development of the Abdominal Viscera Flashcards
Objectives: Explain embryonic origin of adult abdominal viscera
Ventral Mesentery Origin + Named Parts (Falciform, Lesser Omentum, Hepatogastric, Hepatoduodenal)
- Ventral Mesentery: Origin
- Growth of liver causes bulge into abdominal cavity; pulling Septum transversum
- Double Layer of Peritoneum (Ventral Mesentery) suspends between foregun and anterior abdominal wall
- = Derived from Inferior Region of Septum Transversum
- Ventral Mesentery: Named Parts
- Falciform Ligament
- Connects liver to abdominal wall; free margin carriers umbilical vein
- Lesser Omentum
- Connects liver to foregut
- Hepatogastric Ligament
- Connects liver to stomach
- Hepatoduodenal Ligament
- Connects liver to duodenum
- Carries portal triad: Hepatic A., Portal V., Bile Duct
- Falciform Ligament
Objectives: Explain developmengal basis of peritoneal-organ relationships
Objectives: Explain developmental basis of congenital malformations
Objectives: Explain the clinical significance of dual innervation and blood supply to the anal canal
Explain the development of the esophagus?
Region of gut?
- Esophagus:
- Region: Foregut
- Formed by tracheoesophageal septum in foregut tube
- Separated from trachea by esophagotracheal ridge
Explain the development of the stomach
Region of gut?
Impact on Vagus N.?
- Stomach
- Region: Foregut
- Starts as dilation in tube
- Dorsal Surface grows faster (becomes greater curvature)
- Rotates 90 degrees and slightly clockwise
- Rotation results in formation of Lesser Sac
- Impact of Vagus: Rotation of Stomach spins them
- Anterior = Left
- Posterior = Right
Explain the development of the liver?
Region of gut?
- Liver:
- Region: Foregut
- Develops as bud - Hepatic Diverticulum off of foregut
- Grows ventral, pushing into inferior septum transversum
- Growth pulls Septum Transversum along; liver becomes suspended by Ventral Mesentery
- Septum transversum becomes Central Tendon of Diaphragm; not covered by visceral peritoneum (bare area)
Explain the development of the Gall Bladder and Pancreas
What becomes the bile duct?
What causes migration of ventral pancreas and bile duct?
What occurs as pancreatic buds fuse; and what is the fate of the ventral and dorsal ducts?
What is unique about the ventral duct?
- Arise from Hepatic Diverticulum
- Dorsal Pancreas develops as bud off dorsal developing duodenum
- The Common Stalk of the Liver and Gall Bladder becomes the bile duct
- Rotation of duodenum causes ventral pancreas and bile duct to migrate dorsally
- As pancrease fuses, ducts anastomose
- Ventral Duct = Main pancreatic duct; opens with common bile duct on 2nd part of duodenum
- Smaller duct, initial development with bile duct drives persistence as main duct
- Dorsal Duct = May persist as accessory pancreatic duct
- Ventral Duct = Main pancreatic duct; opens with common bile duct on 2nd part of duodenum
Clinical: Annular Pancreas
- Rare congenital abnormality
- Ring of pancreatic tissue encircles descending portion of duodenum
- Cause: Incomplete rotation of the pancreatic ventral bud
Explain the development of the spleen?
How is it unique?
- Not an outgrowth of the gut
- Forms as independent condensation of mesoderm
- Part os mesentry fuses with posterior abdominal wall
Explain midgut development
What is Physiological Umbilical Herniation?
Gastroschisis
Omphalocele
- Liver and midgut grow fast; as midgut elongates, intestinal loops project into the umbilical cord (Physiological Umbilical Herniation); normal!
- Gastroschisis: Ventral body wall defect that results in herniation of intestinal loops into the amniotic cavity; caused by failure of body wall to close
- Omphalocele: Ventral body wall defect that results when parts of the gut tube that normally herniate into the umbilical cord to fail to return to abdominal cavity
Explain the concept of midgut rotation
How many times does it rotate?
What is Meckle’s Diverticulum?
- When intestines project into umbilical cord, midgut loop rotates 90 degress CCW along axis of Superior Mesenteric Artery and Vitelline Duct
- Cecum forms as a swelling on the distal (caudal) loop
- As intestines return to abdomen, they rotate another 180 degrees CCW (270 deg total)
- Meckle’s Diverticulum: Persistence of Vitelline Duct
Explain hindgut development
Cloaca?
Proctoderm?
What is the fully formed anal canal derived from? What is the separation of these sources?
- Cloaca: Part of hindgut proximal to the cloacal membrane
- Urogenital Septum divides into:
- Urogenital Sinus (Anterior)
- Anorectal Canal (Posterior)
- Urogenital Septum divides into:
- Proctoderm: Indentation of body wall that pushes inward toward anorectal canal to form distal opening of tube
- The fully formed anal canal is derived from both cloaca (hindgut) and proctodeum (body wall); their separation is the Pectinate Line
- Above Line - Inferior Mesenteric / Autonomic
- Below Line - Internal Iliac / Spinal Nerves
