Alimentary, Hepatobiliary Systems, Pancreas and Spleen MCQs

The muscle of the upper portion of the esophagus is skeletal muscle, derived from branchial arch VI and innervated by recurrent laryngeal branches of vagus nerve, X. The lower part of the esophageal wall is smooth muscle from splanchnic mesoderm, like the rest of the gut wall. It is innervated by parasympathetics from vagus. Reference - Textbook of Langman's, 12th Edition, Digestive System Embryology Page number - 208

Pancreas forms from endodermal diverticula from the hepatic bud and the duodenum. The ventral bud develops into the uncinate process, but if it rotates abnormally it can cause an annular pancreas. Insulin secretion begins around the 5th month of development. Reference - Textbook of Langman's, 12th Edition, Digestive System Embryology Page number - 208

The spleen develops from the mesoderm in the dorsal mesogastrium. The mesenchymal cells in the dorsal mesogastrium form small lobular masses of splenic tissue called spleniculi. Later, these lobules fuse to form a single mass of the spleen. The capsule, septa, and connective tissue framework, including reticular fibers, develop from mesoderm. The mesenchymal cells also differentiate into lymphoblasts and other blood-forming cells. Reference - Textbook of Langman's, 12th Edition, Digestive System Embryology Page number - 219

Incomplete separation of cloaca by the urorectal septum causes anal agenesis. When the urorectal septum is formed, the cloacal membrane gets divided into urogenital membrane anteriorly and anal membrane posteriorly. The ectoderm in the region of the future anal opening is called proctodeum. The proctodeum invaginates and creates the anal pit. The anal membrane now separates the hindgut from the anal pit. Formation of the anal canal takes place as follows: The upper part of the anal canal is formed by the endodermal hindgut and the lower part by the ectodermal anal pit. The anal membrane in between breaks around the 9th week and the anal canal becomes continuous. The junction between the endodermal and the ectodermal region of the anal canal is marked by the pectinate line. Reference - Textbook of Langman's, 12th Edition, Digestive System Embryology Page number - 208

Duodenum develops from caudal foregut and cranial midgut. Except for the short first part and end of the fourth part, the duodenum becomes retroperitoneal after rotating to the right. Epithelial overgrowth temporarily obliterates the duodenal lumen, and duodenal stenosis or atresia may result from failed recanalization. Reference - Textbook of Langman's, 12th Edition, Digestive System Embryology Page number - 208

Meckel's diverticulum is from the vitelline duct. Urachal fistula is a persistent allantoic duct. Cystic kidney results from failure of the collecting ducts to meet the metanephric blastema. Spina bifida cystica is a herniation of the spinal cord through a defective vertebral arch. Reference - Textbook of Langman's, 12th Edition, Digestive System Embryology Page number - 211

The midgut rotates in a counterclockwise direction around superior mesenteric artery. Persistence of the vitelline duct may cause a vitelline fistula or cyst. Omphalocele results from a failure of midgut to return to the abdominal cavity, while congenital umbilical hernia is a later herniation of gut through abdominal wall. Reference - Textbook of Langman's, 12th Edition, Digestive System Embryology Page number - 222

Failure of the intestinal loops to return to the abdominal cavity during the 6th to 10th weeks results in omphalocele or exomphalos. Omphalocele is a congenital malformation in which the abdominal viscera protrudes through a wide umbilical defect. The bowel loops are covered by amnion. A small omphalocele contains only the intestines. A large omphalocele may contain other viscera such as the stomach, liver, spleen, and large intestine, along with the small intestine. Omphalocele is commonly associated with other congenital anomalies (e.g., trisomy 13, trisomy 18, or Beckwith-Wiedemann syndrome) and causes increased levels of a-fetoprotein. Reference - Textbook of Langman's, 12th Edition, Digestive System Embryology Page number - 219