TBL17 - Dorsal and Ventral Mesenteries

Question 1

What suspends the gut tube from the dorsal body wall? Where does the structure extend from and to? Where are mesenteries formed?

Answer 1

1) The gut tube is suspended from the dorsal (posterior) body wall by the dorsal mesentery
2) The mesentery extends from the abdominal portion of the esophagus to the end of the hindgut
3) Mesenteries are formed at sites of continuity between the parietal and visceral peritonea

Question 2

What is the septum transversum derived from and what does it surround? What does the ventral mesentery do and what is it derived from?

Answer 2

1) The septum transversum is derived from visceral (splanchnic) mesoderm that surrounds the heart tube
2) The ventral mesentery, which connects the abdominal portion of the esophagus, the stomach, and proximal duodenum to the ventral (anterior) body wall, is derived from the septum transversum

Question 3

What is the liver bud and what does it grow into? What does growth of the liver within the septum transversum separate? What does the septum transversum become?

Answer 3

1) The liver bud, an endodermal outgrowth from the proximal duodenum, grows into the septum transversum
2) Growth of the liver within the septum transversum separates the ventral mesentery into the falciform ligament and lesser omentum
3) The septum transversum becomes the central tendon of the diaphragm

Question 4

What is the fusiform stomach suspended by?

Answer 4

The fusiform stomach is suspended from the dorsal body wall by the dorsal mesogastrium, which is the portion of dorsal mesentery associated with the stomach

Question 5

What does the fusiform stomach do to position itself correctly? What occurs during this rotation?

Answer 5

1) The fusiform stomach rotates 90⁰ clockwise around its longitudinal axis, which causes its left side to face anteriorly and its right side to face posteriorly
2) During the rotation, the original posterior wall grows faster than the original anterior wall thereby creating the greater and lesser curvatures of the stomach

Question 6

What does additional rotation of the stomach do? What is the result of the rotation in relation to the shape of the duodenum?

Answer 6

1) Additional rotation of the stomach around its antero-posterior axis moves its distal part to the right and upward and its proximal part to the left and downward
2) This rotation pulls the duodenum to the right thereby creating its characteristic C-shaped loop

Question 7

What does the rotation of the stomach cause the dorsal mesogastrium to do? What does the descending portion of the looping greater omentum do?

Answer 7

1) The rotation causes the dorsal mesogastrium to bulge downward from the greater curvature as the double-layered greater omentum
2) The descending portion of the looping greater omentum fuses with the ascending portion to create its four-layered structure

Question 8

Where do the primordia of the pancreas and spleen originally reside? What do the stomach rotations do to the mesenteries and what does this cause?

Answer 8

1) Primordia of the pancreas and spleen originally reside in the dorsal mesentery and dorsal mesogastrium, respectively
2) The stomach rotations pull the mesenteries to the left where the dorsal mesentery partially fuses with the parietal peritoneum of the posterior body wall and places the pancreas in its retroperitoneal location

Question 9

What does the dorsal mesogastrium enclose the spleen as and what does it create? What forms the splenorenal ligament and what does this ligament do?

Answer 9

1) The dorsal mesogastrium encloses the spleen as visceral peritoneum and creates the gastrosplenic (ignore gastrolienal) ligament that connects the stomach to the spleen
2) The non-fused portion of the dorsal mesentery forms the splenorenal ligament that connects the spleen to the body wall in the region of the retroperitoneal left kidney