The Development Of The Gi Tract Flashcards
What does the folding of the embryo in the 4th week create?
Laterally creates the ventral body wall and the primitive gut become tubular, craniocaudally creates cranial and caudal pockets from yolk sac endoderm beginning the primitive gut development
What are the emboryonic divisions of the gut?
Rh foregut the midgut and the hind gut foregut and the hindgut begin ass blind whereas the midgut is continuous with the yolk sac
When does the development of the primitive gut tube begin?
Begins in the third week where it pinches off from the yolk sav cavity
What is the internal lining of the gut tube dervived from?
Endoderm
What is the external lining of the gut tube dervived from?
The spalnic mesoderm, which forms the future musculature and the visceral perioteunum
How is the primitive gut tube suspended in the intraemobryonic colem?
By a double layer of spalhnic mesoderm
What are the adult derviatives of the foregut?
The oesphagus, the stomach, the pancreas the liver and the gall bladder and the duodenum(proximal to the entrance of the bile duct)
What are the adult deriviatives of the midgut?
The dudoenum, the jejunum, the ileum, the cecum, the ascending colon and the proximal 2/3 of the tranverse colon
What are the adult derviatives of the hindgut?
The distal 1/3 of the transverse colon, the descending colon, the sigmoid colon, the rectum, the upper anal canal and the internal lining of the bladder and the urethra
Where does foregut derivied organs get their blood supply from?
The celiac trunk
Where do midgut derivied organs get their blood supply from?
The SMA
Where do hindgut derivived organs get their blood supply from?
The IMA
What are the structures in the gut that may end up with a mixed blood supply?
The dudoenum, proximal to the entry of the bile, the gastroduogenal and the superior pancreaticodudoenal ateries and distal to the entry of the bile duct is the inferior pancretaiotideal, the head of the pancreas is supplied by the coliec tranc, and the SMA
What are the two parts of the mesoderm involved in development of the gut?
The somatic and the splanchic mesoderm
What is a mesentary?
A double layer of periotenum suspending the gut tube from the abdominal wall
How are mesentaries fromed?
The new primitive gut tube is suspended with the intraemobryonic ceoluem, the splanchnic mesoderm surround the new gut and the mesentery is formed from a condensation of this mesoderm
Where do you find the different mesentaries?
He dorsoal medsentary suspends the entire gut tube of the dorsal body wall whereas the ventral mesentery is only found in the foregut region
How do you form the greater and lesser peritoneal sacs?
The dorsal and ventral mesentays in the region of the foregut divide the cavity into left and right sacs in this region only, the left sace contributes to the greater sac whereas the right sac becomes the lesser sac that comes to lie behind the stomach
How is the greater omentum formed?
Formed from the dorsal mesentary and is the frist structure seen when the abdomen is opened anteriorly
How is the lesser omentum formed?
It is formed from the ventral mesentary and the free edge conducts the portal triad
What is the one proccess that leads to the formation of the greater and lesser sacs and the omenta?
Rotation
How does the rotation of the stomach occur?
The primitive stomach rotates in two directions, around the longitudinal axis and around the anteroposterior axis, adn the result is that the greater and lesser curvature come to lie first of the left and right side and the cardia and the plyrous move horizontally and pull the curvature inferiorly
What does rotation of the stomach result in?
Pulls the vagus nerves anterior and posterior to the stomahc instead of left and right, shifts the cardia and the pylorus from the midline so that the stomach lies obliquely, contributes towards moving the lesser sac behind the stomach and creates the greater omenum
What is a peritoneal refelction?
A change in direction from parietal peritoneum to mesentery, from mesentery to visceral peritoneum and from visceral peritoneum……
What happens when there is no mesentary?
Structures that are not suspened within the abdominal cavity are retroperitoneal
What are the two types of retropertioneal organs?
There are retropertionelal organs that were never in the periotneal cavity had a mesentary, and then there are secondary retropertioneal organs that began development invested by peritoneum and mesentary but with successive growth and devleopment the mesentary is lost throug fusion ret
How is the stomach formed emboryologically?
Mid week four slight dilation of the distal foregut indicates the position of the stomach primodrium, and faster growth of the dorsal border creates the greater curvature of the stomach, and then rotates changing the positions of the dorsal and the ventral mesentaries, and forming the omental burs and making sure that the lesser sac is displaced posteriorly
What are the glands formed in the ventral mesentary?
Liver, the biliary system and parts of the pancreas such as the uncinate process and the inferior head
What are the glands derived from the dorsal mesentery?
Pancreas, the superior head and the neck, body and tail
What does the liver from from?
The hepatic bud within the ventral mesentery
What does the duodenum develop from?
Develops from the caudal foregut and the cranial midgut, and grows rapidly and forms a c shaped loop when the stomach rotates
What are the second degree retropertineal structures of the foregut?
The duodenum (except the duodenal cap) and the pancreas
What is the primary intestinal loop?
The midgut elongates enourmasly and runs out of space in the abdominal cavity, makes a loop that has a cranial and caudal limb and the superior mesenteric artery as the axis, and is connected to the yolk sace by the vitelline duct
What is physiological herniation?
During the 6th week the growth of the primary intestinal loops is very rapid, as well as the liver adn therefore the abdominal cavity is not large enough to accomadat both, and therefore the intestines herniate into the umbilical cord.
What is roatation of the midgut?
3 x 90 defgress counterclockwise rotations around the axis formed by the SMA, during herniation and the return of the gut to abdominal cavity
What is the consequence of rotation of the midgut?
The cranial limb returns to the abdominal cavity first
What are some of the features of retraction of the herniated loop?
During the 10th week the herniated loops return to the abdomianl cavity, the proximal part of the jejunum is the first return, and the caceal bud is the last, it lies in the right upper quadrant at first and therefore has to descend back to the pelvic region
What structures are dervived from the cranial limb of the midgut loop?
Distal duodenum, jejunum and the proximal ileum
What sturctures are dervived caudal limb of the midgut?
The distal ileum, cecum, the appendix, descenindg colon adn the proximal 2/3 of the traverse colon
What is the result of incomplete rotation?
Where the midgut makes only one 90 degree rotation, you get a left sided colon
What is the result of reveresed rotation?
If it rotates only 90 degrees clockwise, the tranverse colon will pass postetrior to the ileum
What is a vitelline cyst?
Boths ends of the vitelline ducts are firbous cords but it remains patent in the middle, the loops may twist and become straungulated
What is a vitelline fistula???
The vitelline duct remains patent over its entire length, therefore there is a communication between the umbilicus and the gi tract, and therefore fecal dischargee may be found at the umbilicus
What is a meckels diverticulum?
This is an outpuching of the ileum caused by some of the vitelline duct remaining patent, is normal asymptomatic unless it contains ectopic tissue such as pancreatic tissue
Why does the process of recanalisation occur?
In some sturctures, such as the osephagus the bile duct and the small intestine, the growth occurs so rapidly that the lumen of the primitive gut tube is obliterated, and therefore recanalisation occurs to restore the lumen
What can occur if rencanlisation is incomplete?
An atresia or a stenosis
What is a pyloric stensois?
This is not a stenosis that occurs as a result of rencanalisation failure, rathe of heterotrophy of the circular muscle in the region of the pyloric spinther, that therefore results in characterisitc projectile vomiting
Wha tis a gastrochisis?
A failure of closure of the abdominal wall during folding of the emborying, cuaisng gut contents not covered in aminon to come out
What is a ompahlocele?
A persostance of physiological herniation
What is the cloaca and what happens to it diring development?
At 6 weeks the hindgut ends in the cloaca, and is seperated from the outside by the cloacal membrane, and is subject to antero posterior divisioning, as a wedge of mesoderm foes down into the cloaca
What are the features of the anus above the pectinate line?
Coloumnar epithelium, IMA S2, 3 4 parasymaptheic.
What are some of the features of the anus below the pecinate line?
Is a stratifed epithelium,
What are some hindgut abnormalities?
An impeforate anus, which is a failure of the anal membrane to perforate, anal or anorectal agenesis and hindgut fistuale
