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28 Cards in this Set
- Front
- Back
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Outline the development of the primitive gut tube stating its tissue of origin.
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In 3rd week of development the primitive gut tube is formed by cephalocaudal and lateral folding, when part of the endoderm lined yolk sac is incorporated into the embryo.
- Lateral folding – primitive gut tube becomes tubular, creates ventral body wall. - Cranialcaudal folding – creates cranial and caudal pockets from yolk sac endoderm. The gut tube is a blind ended tube comprising of the foregut at the cephalic end, the hindgut at the caudal end and the midgut in the middle which is still attached to the yolk sac via the vitelline duct (yolk stalk – the umbilicus.) The internal lining of the gut tube is endoderm, surrounded by visceral (splanchnic) mesoderm. The gut tube is suspended within the intraembyonic cavity by a double layer of splanchnic mesoderm – mesentery. |
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What does splanchnic mesoderm, the external lining of the primitive gut, develop into?
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- Visceral peritoneum
- Smooth muscles and blood vessels of viscera |
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Describe mesenteries
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A Mesentery is double layer of peritoneum that encloses an organ and connects it to body wall. These organs are called intraperitoneal organs whereas those that lie against the posterior abdominal wall and are only covered by peritoneum on their anterior surface are retroperitoneal. Mesenteries can pass from one organ to another as well as to a body wall. They carry nerves, blood vessels and lymphatics to and from abdominal viscera.
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Describe dorsal and ventral mesenteries
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By the 5th week the lower part of the foregut, the midgut and most of the hindgut are suspended from the abdominal wall by the dorsal mesentery. The dorsal mesentery extends from the lower part of the oesophagus to the cloaca.
- In the region of the stomach it forms the greater omentum ( dorsal mesogastrium) - in the region of the duodenum it forms the dorsal mesoduodenum - in the area of the jejuna and ileal loops it forms the mesentery proper - At the part of the colon it forms the mesocolon. The ventral mesentery only exists for the foregut from the lower end of the oesophagus to the upper part of the duodenum. It is derived from the septum transversum. The liver grows into the mesenchyme of the septum dividing it into the lesser omentum ( between the stomach and liver) and the falciform ligament between the liver and the ventral body wall. The dorsal and ventral mesenteries divide the cavity into left and right. The left sac contributes to the greater sac and the right sac becomes the lesser sac behind the stomach. |
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What does the foregut comprise of and what is its blood and nerve supply?
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The foregut comprises of the oesophagus, stomach, pancreas, liver, gall bladder, duodenum proximal to entrance of bile duct.
The foregut is supplied by the celiac trunk. Parasympathetic innervations is via vagus nerve and sympathetic innervation is via the greater splanchnic nerve ( T5-T9) |
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What does the midgut comprise of what is its blood supply and nerve supply?
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The midgut comprises of the duodenum distal to the entrance of the common bile duct, the jejunum, ileum, caecum, appendix, ascending colon and the proximal 2/3 transverse colon.
It is supplied by the superior mesenteric artery. It is innervated by the parasympathetic branch via the vagus nerve and sympathetic innervation by the middle splanchnic nerve ( T10-T11) |
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What does the hindgut comprise of what is its blood supply?
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The hindgut comprises of the distal ½ of the transverse colon, the descending colon, the sigmoid colon and the rectum and supplies the endoderm lining of the bladder and urethra.
It is supplied by the inferior mesenteric artery and innervation is from the inferior mesenteric plexus. The sympathetic innervation is via lumbar splanchnic nerves ( L1-L2) and parasympathetic innervations is from S2-S4). |
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Which structure of the gut are likely to have mixed blood supply and why?
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Structures which develop close to the borders between forefut and midgut will have mixed blood supply.
The 1st part of the duodenum and the head of the pancreas have mixed blood supply. The head of the pancreas lies within the curve of the duodenum. The superior pancreaticoduodenal artery, a branch from the gastroduodenal artery lies in the gap between the duodenum curve and the head of the pancreas along with the inferior pancreaticoduodenal artery, a branch of the superior mesenteric artery. There is mixed blood supply from foregut ( celiac trunk – gastroduodenal artery) and midgut derivatives ( superior mesenteric artery). |
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Define stomatodeum and proctodeum.
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Future mouth and future anus
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Describe Oesophagus formation!
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At 4 weeks the respiratory diverticulum appears on the ventral wall of the foregut at the pharynx. The tracheoesophageal septum gradually separates the trachea from the oesophagus. The trachea lays ventral and the oesophagus dorsal. The oesophagus lengthens with descent of the heart and lungs and in an adult is 25cm long. The skeletal muscular walls in the upper 2/3 of the oesophagus, which are formed by splanchnic mesenchyme, are innervated by the vagus nerve. The lower 1/3 is smooth muscle which is innervated by splanchnic plexus.
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Describe some oesophageal abnormalities.
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If the oesophagus fails to lengthen fully, the stomach will be pulled up into the thorax, through the oesophageal hiatus of the diaphragm producing a congenital hiatal hernia.
Oeophageal atresia is the closing of the oesophagus so that normal passage of amniotic fluid cannot pass into the intestinal tract and this results in polyhydramnios. In addition the lumen of the oesophagus may narrow, oesophageal stenosis. Tracheoesophageal fistula are connections remaining between the trachea and oesophagus. Oesophaegeal atresia and tracheoesophageal fistula may form from spontaneous posterior deviation of the septum or from a mechanical factor pushing the dorsal wall of the foregut anteriorly. |
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Describe Stomach formation!
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The stomach originates as a fusiform swelling of the foregut in week 4. It rotates 90 clockwise around its longitudinal axis so that the original left side faces anteriorly and the original right side faces posteriorly. Therefore the left vagus nerve innervates the anterior stomach surface and the right vagus nerve innervates posterior stomach surface. The original posterior wall grows faster than the original anterior wall forming the greater and lesser curvatures. The stomach then rotates along its anterioposterior axis so that the caudal/pyloric end rotates to the right and up and the cephalic/cardiac end moves to the left and down. The rotation of the stomach takes its ventral and dorsal mesenteries with it. The dorsal mesogastrium (greater omentum) is pulled to the left in the longitudinal rotation, creating a space behind the stomach called the omental bursa (lesser peritoneal sac). The greater momentum hangs down from the greater curvature in front of the transverse colon and the duplicated layers of the greater ometum fuse. The posterior surface of the greater omentum fuses with the mesentery of the transverse colon. The ventral mesogastrium is pulled to the right.
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Describe the positioning of the spleen.
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The spleen arises within the dorsal mesogastrium. During longitudinal and anteroposterior rotation of the stomach, the dorsal mesogastrium lengthens and the part between the spleen and the dorsal midline swings to the left and fuses with the peritoneum of the posterior abdominal wall. The spleen remains intraperitoneal and is connected to the body wall in the region of the left kidney by the spleenorenal ligament (lienorenal) and to the stomach via the gastrolienal ligament.
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Describe the positioning of the pancreas.
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The pancreas lies in the mesoduodenum but during longitudinal and anteroposterior rotation of the stomach, as well as the extreme growth of the liver in the ventral mesogastrium, the pancreas’s tail extends into the dorsal mesogastrium. It is pushed against the body wall and the peritoneum disintegrates on the posterior wall so it becomes a secondary retroperitoneal structure.
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Describe the future of the ventral mesogastrium
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The ventral meogastrium derives from the septum transversum. Liver cords grow into the septum from hepatic bud, it thins to form the peritoneum of the liver, the falciform ligament attaching the liver to the abdominal wall and the lesser omentum attaching the liver to the stomach. The falciform ligament contains the umbilical vein which after birth becomes the ligamentum teres hepatis. The free margin of the lesser omentum connecting the liver and duodenum ( hepatoduodenal ligament) contains the portal triad –the bile duct, portal vein, hepatic artery and lymphatics. The free margin also forms the roof of the foramen of winslow which is the opening of the omental bursa (lesser sac) with the rest of the peritoneal cavity (greater sac).
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What is the lesser sac?
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The lesser sac is a pouch of the peritoneal cavity behind the stomach. It communicates with the rest of the peritoneal cavity via the epiploic foramen (of Winslow); the foramen is also called the entrance to the lesser sac.
Developmental changes in the abdomen result in the formation of the lesser sac. The stomach which is symmetrical to begin with enlarges and expands unevenly, mainly towards the left. (It also rotates so that its original left side becomes anterior and the right side comes to lie posteriorly.) Expansion and rotation of the stomach draws its dorsal mesentery into a sac (or “pouch”), the lesser sac or omental bursa; this becomes the greater omentum. The ventral mesentery becomes the lesser omentum. |
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What are superior, inferior and posterior relations of the entrance of the lesser sac?
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Superior – caudate lobe of the liver
Inferior – superior part of the duodenum Posterior – peritoneum covering the inferior vena cava and right crus of the diaphragm; the abdominal aorta lies left of these structures |
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Which structures lie in the free border of the lesser omentum?
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The structures that lie in the free border are those that are supplying blood to the liver and transporting the secretions (bile) of the liver into the duodenum. The blood vessels are the hepatic artery (a branch of the common hepatic artery originating from the coeliac trunk) and the hepatic portal vein conveying the venous portal blood from the gut to the liver. The bile is transported to the duodenum by the common bile duct.
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Describe the forgut derived glands
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Ventral mesogastrium – liver from hepatic bud, billary system, uncinate process and inferior head of pancreas
Dorsal mesogastrium – superior head of pancreas, tail and body |
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Which structures of the foregut are secondary retroperitoneal.
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Structures which begin life as intraperitoneal surrounded by a peritoneum with mesentery but during their development are pushed close to the posterior abdominal wall that they lose their posterior peritoneum, becoming retroperitoneal.
As the stomach rotates the duodenum becomes a C shaped loop and rotates to the right. The duodenum and head of the pancreas push against the dorsal body wall and the right surface of the dorsal mesoduodenum fuses with the adjacent peritoneum and disappear. The duodenum and head of the pancreas become fixed retroperitoneal structures. The dorsal mesoduodenum disappears entirely except in the region of the pylorus of the stomach where a small portion of the duodenum (the duodenal cap) retains its mesentery and remains intraperitoneal. |
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What happens to the lumen of the duodenum during development?
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The lumen of the duodenum is obliterated by proliferation of cells in its walls and then recanalised.
Name the retroperitoneal structures. Kidneys, adrenal glands, ureters, aorta, vena cavae, 2nd and 3rd part of duodenum, pancreas, ascending and descending colon, oesophagus and upper portion of rectum |
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What is the Peritoneal cavity?
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The peritoneal cavity is a potential space than exists between the two layers of peritoneum. It only contains a small amount of fluid (no organs). Ascites is a pathological condition where the amount of fluid contained within the peritoneal cavity increases. The peritoneal cavity in men is a closed space, while in women it communicates with the reproductive organs through the infundibulum of the fallopian tubes
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List the functions of the peritoneum.
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o To reduce the friction between various abdominal viscera as they move, eg during persistalsis
o To reduce the spread of infection within the abdominal cavity o Suspend the viscera o Pathway for neurovascular structures |
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What is the difference between the Visceral and Parietal peritoneum?
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Although actually one continuous sheet, the Visceral peritoneum invests viscera while the parietal peritoneum lines the internal surfaces of the abdominopelvic wall.
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What factors may distend the abdomen?
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The 6 Fs:Fat, flatus, faeces, fluid, fetus, food and malignant states of the abdominal viscera.
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The peritoneal cavity is a space that normally contains only a few millilitres of fluid. To what volume may that space be distended by pathological conditions?List the common substances that may occupy or distend the peritoneal cavity as a result of a pathological process.
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Over 3 litres of fluid can accumulate in the cavity. The fluid is a transudate (a protein free filtrate of blood plasma) e.g. from portal hypertension or an exudate (a protein containing fluid) which usually exudes from malignant surfaces.
The common substances that distend the peritoneal cavity are Fluid, blood, urine, pus, contents of perforated bowel, air (gas). |
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What are the subphrenic spaces and why are they important?
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These are spaces (anterior and posterior) between the liver and diaphragm on the right side of the body. They are sites of collection of inflammatory fluids that may go undetected. Fluids collect there when a patient is lying supine in bed.
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At what vertebral level does the oesophagus, IVC and aorta enter the abdominal cavity?
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IVC - T8
oesophagus - T10 Aorta - T12 I ate ten eggs at 12 |
