Module 5

Question 1

GI Track

Answer 1

The GI tract initially arises during the process of gastrulation from the endoderm of the trilaminar embryo

Question 2

Ectoderm

Answer 2

Gives rise to the enteric nervous system

Question 3

Mesoderm

Answer 3

Gives rise to connective tissues, smooth muscle, blood vessels, and mesentery of the GI tract

Question 4

Endoderm

Answer 4

Source of the epithelial lining of the GI tract, liver, gallbladder, and pancreas

Question 5

Primitive Foregut

Answer 5

The foregut extends from the oral cavity to the initial part of the duodenum (supplied by the celiac artery)

Question 6

Primitive Midgut

Answer 6

The Midgut extends from the mid-duodenum to the initial two-thirds of the transverse colon (supplied by the superior mesenteric artery)

Question 7

Primitive Hindgut

Answer 7

The hindgut extends from the distal one-third transverse colon to the upper portion of the anus (supplied by the inferior mesenteric artery)

Question 8

Mesentery

Answer 8

The mesentery is a double layer membrane formed by the fusion of the splanchnic mesoderm. Suspends the gut tube and it’s derivatives from the dorsal and ventral wall

Question 9

Dorsal Mesentery

Answer 9

The dorsal mesentery is composed of the: mesogastrium (greater omentum), mesoduodenum, mesentery proper (of the small intestine), and mesocolon

Question 10

Ventral Mesentery

Answer 10

The ventral mesentery is derived from the septum transversum and forms the falciform ligament of the liver and the lesser omentum

Question 11

Development of the Esophagus (Elongation, Occlusion, Recanalization)

Answer 11

After the trachea separates from the esophagus, the esophagus continues to grow in length to keep up with the overall growth of the embryo. This growth is known as elongation and is responsible for the repositioning of the stomach in the abdomen. Around the 5th week of development, proliferation of the endoderm results in occlusion of the esophagus. Recanalization of the esophagus occurs around the 9th week of development resulting in the formation of a hollow tube

Question 12

Anatomy of the Stomach

Answer 12

The stomach is a digestive organ located between the esophagus and the duodenum
It is made up of four anatomical regions continuous with the esophagus and duodenum: the cardia, fundus, body, and pylorus

Question 13

Development of the Stomach

Answer 13

The stomach appears as a gastric dilatation in the foregut during the fourth week of development. During subsequent weeks, the stomach grows and rotates along a longitudinal and anteroposterior axis

Question 14

Longitudinal Rotation

Answer 14

Initially, the stomach is oriented in the median plant and is suspended from the dorsal wall of the abdominal cavity. During development, the stomach rotates right 90 degrees about the longitudinal axis . Concurrently with this rotation, differential growth along one border of the gastric dilation causes it to elongate more rapidly than the other, producing the greater curvature of the stomach and the smaller lesser curvature

Question 15

Anteroposterior Rotation

Answer 15

With increased growth, the stomach rotates about its anteroposterior axis; the pylorus moves cranially and the cardia moves caudally

Question 16

Stomach Rotation on the Mesentery

Answer 16

Rotation of the stomach carries its dorsal border (and its mesentery) to the left. - The rotation pulls the dorsal mesogastrium (greater omentum) to the left, thereby creating the omental bursa (lesser sac). The dorsal mesentery thus forms the greater omentum and the gastrosplenic and splenorenal ligaments
The ventral mesentery or septum transversum forms the capsule and peritoneal coverings of the liver and the ligaments of the liver: lesser omentum and triangular, coronary, falciform ligaments.

Question 17

Development of the Liver and Gallbladder

Answer 17

The development of the liver and gallbladder are closely linked as they both arise from the hepatic diverticulum

Question 18

Hepatic Diverticulum

Answer 18

The liver develops from cells that form the hepatic diverticulum. The hepatic diverticulum grows from the distal end of the foregut (middle part of duodenum) and penetrates the septum transversum (which forms the diaphragm). As it grows, the hepatic diverticulum divides into a cranial part, which forms the parenchyma of the liver and the caudal part, which will layer give rise to the gallbladder and cystic duct. As hepatic cells continue to penetrate the septum transversum, the connection between the diverticulum and the foregut narrows, forming the hepatic duct. Forms the hepatic duct, an outgrowth gives rise to the gallbladder and the cystic duct; the hepatic and cystic ducts together form the bile duct. During further development, epithelial liver cords differentiate (from endoderm) into the liver parenchyma (functional hepatocytes) and form the lining of the biliary ducts (including bile, cystic, and hepatic ducts). The connective tissue capsule of the liver is derived from the septum transversum

Question 19

Development of the Pancreas and Duodenum

Answer 19

The pancreas develops from two outgrowths of the gut tube endoderm: the dorsal pancreatic bud which originates from the duodenum, and the ventral pancreatic bud which develops from the bile duct. The ventral pancreatic bud migrates dorsally (clockwise) to come into close contact with the dorsal pancreatic bud. The proximal duodenum also rotates clockwise with the pancreas, both resting retroperitoneally. Each bud has its own duct. The duct of the ventral pancreatic bud is connected to the bile duct. The ventral bud fuses with the dorsal bud and the ventral bud becomes the uncinate process of the pancreas. The dorsal pancreatic bud makes up the main body of the pancreas The ducts of the pancreatic buds also fuse causing the main pancreatic duct and the biel duct to unite