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WEEK 1:
Embryology of abdominal viscera 1:
| Question | Answer |
|---|---|
| when does the primitive gut tube form | when dorsal part of yolk sac is incorporated into the embryo due to folding of the embryo |
| where does the primitive gut tube span | oropharyngeal membrane to the cloacal membrane |
| where are the mucosal lining and glands derived from in the primitive gut | endoderm (everything else are mesodermal derivatives) |
| what happens to the epithelial lining of the gut during early development | proliferates rapidly and partly or completely obliterates the lumen and the resultant solid-mass gut tube gets recanalized later |
| folding of embryo takes place during | 4th week |
| what happens at the 4th week | embryo folds turning it from flat disc into three dimensional shape |
| where does folding of embryo occur | all around periphery of embryonic disc (longitudinal and transverse) |
| flat region of endoderm is modified into | deep tube to become the primordial foregut |
| where does the embryo fold from | head (longitudinal/ cephalocaudal folding) |
| what happens at end of 4th week | visceral mesoderm layers are continuous with parietal layers as a double layered membrane (dorsal mesentery) |
| where does the dorsal mesentery extend from | caudal limit of foregut to end of hindgut |
| internalised yolk sac becomes | primitive gut |
| how are the foregut, midgut, and hindgut made | during folding the longitudinal plane, part of the yolk sac is pinched off and remains within the embryo |
| celiac artery supplies | foregut (distal oesophagus, stomach, and superior half of duodenum) |
| superior mesenteric artery supplies | midgut (inferior half of the duodenum, ileum, jejunum, caecum, appendix, ascending colon and 'half transverse colon') |
| inferior mesenteric artery supplies | hindgut (rest of the transverse colon, descending and sigmoid colon, rectum, and upper 2/3 of the anal canal) |
| where does the stomach lie at week 4 | in the midline with a body cavity on either side |
| how is the stomach joined to the body wall | via both a ventral and dorsal mesentery |
| where does the ventral mesentery end | more caudally |
| what type of mesentery does the midgut/ hindgut have | dorsal |
| another name for the dorsal mesentery of the embryonic foregut | dorsal mesogastrium |
| describe the growth of the liver bud | grows as an outpouching from the developing duodenum into the ventral mesentery |
| what is the liver bud composed of | gall bladder, system of bile ducts, and ventral part of the pancreas |
| describe the growth of the dorsal part of the pancreas | grows as a similar outpouching as liver bud into the dorsal mesentery |
| describe the growth of the ventral part of the pancreas | grows as an outpouching from the bile duct |
| describe the growth of the gall bladder (and cystic duct) | another bud coming from the bile duct, with the stalk becoming the cystic duct |
| describe the growth of the right and left hepatic ducts | the bile duct divides into the right and left hepatic ducts and these develop into the lobes of the liver, remainder of duct system, and hepatocytes of the liver |
| which part is the greater part of the pancreas | dorsal pancreas |
| explain what happens due to the differential growth of the duodenum | the ventral pancreas and bile duct are displaced behind (posterior) the duodenum, next to the dorsal pancreas and later fuse together |
| what does the ventral pancreas become | uncinate process of the pancreas |
| what does the dorsal pancreas become | head, neck, body, and tail of pancreas |
| describe the formation of the main pancreatic duct | during fusion, most of the original dorsal pancreatic duct joins the ventral pancreatic duct |
| describe the formation of the accessory pancreatic duct | remaining dorsal pancreatic duct becomes the accessory pancreatic duct |
| biliary atresia | failure of main bile duct to form a lumen which progressively leads to deepening jaundice after birth |
| function of cystic duct | connects the gall bladder to common bile duct to transport bile |
| what would happen if the gall bladder bud does not form during development | gall bladder and cystic duct does not form |
| congenital abnormalities that could occur with the liver | gall bladder bud does not form so gall bladder and cystic duct does not form, congenital absence of only the cystic duct so gall bladder opens directly into common hepatic duct , biliary atresia, and annular pancreas |
| what is a treatment/ management for biliary atresia | early surgery, which is critically important to avoid eventual liver failure |
| annular pancreas | occurs when ventral pancreas grows around both sides of gut (around duodenum) which leads to duodenal stenosis |
| what happens to the stomach during the 4th to 6th week | stomach rotates so that its left side becomes its anterior surface |
| the rotation of the stomach causes what | twists the ventral and dorsal mesenteries so that the liver develops on the right and the spleen on the left, helps to pull the duodenum into a 'C' shape, carries duodenum and pancreas against posterior abdominal wall making them (retroperitoneal) |
| the bare area of liver (no peritoneum covering it) results from | direct contact with septum transversum |
| development of liver divides the ventral mesentery into | falciform ligament in front and lesser omentum behind |
| development of spleen divides the dorsal mesentery into | gastrosplenic ligament and splenorenal ligament |
| how does the greater omentum form | from the elongation of the dorsal mesogastrium, which forms the floor of the lesser sac behind the stomach (and hangs down in front of inestines) |
| how does the midgut communication with the yolk sac | via vitelline duct |
| where is the midgut development | suspended from the dorsal abdominal wall |
| describe the speed of the midgut development and what it leads to | rapid elongation creates the primary intestinal loop |
| describe the rotation of the midgut loop | has a 270* counterclockwise rotation around the superior mesenteric artery and elongation of small intestines loop forms the jejunum and ileum as coiled loops |
| atresia meaning | absence of lumen |
| stenoses meaning | narrowing of lumen |
| congenital abnormalities of GIT | atresias, stenoses, abnormal rotations, anterior abdominal wall defects, malrotation eg situs inversus (organs are a mirror image/ flipped on the other side) |
| the commonest form of congenital duodenal stenosis is due to | failure of duodenum to become recanalized (typically occurring caudal to opening of bile duct and is cause of early persistent bile-stained vomiting in the neonate) |
| gastroschisis | congenital fissure in wall of abdomen which DOES NOT INVOLVE UMBILICUS meaning abdominal contents can spill through this defect |
| omphalocoele | congenital hernia in which the abdominal contents protrude into the umbilical cord and is usually associated with other defects |
| duplications of GIT** | abnormal extra segment of GIT developing alongside normal bowel (usually in ileum) which can cause intestinal obstruction, become infected, bleed, cause abdominal pain etc |
| Meckel diverticulum** | congenital pouch arising from ileum due to persistence of vitelline duct (does not disappear) which could lead to bleeding |
| malformations of the anus and rectum (ARMs)** | occurs when developing terminal intestine and anus do not form or separate normally eg normal anal opening is absent or blocked or rectum develops abnormal connection with urethra/vagina |
| aganglionosis (Hirschsprung disease)** | congenital disorder where segment of bowel lacks enteric ganglion cells leading to no normal enteric nervous system and failure of relaxation so bowel remains contracted creating obstruction and bowel contents accumulate above it (constipation, vomiting) |
| superior mesenteric artery (SMA) syndrome** | results from compression of third part of duodenum between SMA and abdominal aorta (where fat usually separates them, fat pad can be reduced leading to less cushioning) leading to post-meal abdominal pain, nausea, and vomiting etc due to low body weight |
Created by:
22tango
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