Development Of The Gut Flashcards
What is gastroschisis?
It is when the lateral body folds do not completely meet and fuse correctly. There is weakness of the anterior abdominal wall which leads to gastroschisis, leading to an open communication between abdominal cavity and outside environment.
What is Ileal (Meckel’s) Diverticulum?
What is fibrous cord, vitelline sinus, vitelline fistula, and vitelline cyst conditions?
The vitelline duct connects the gut tube to the yolk sac.
Normally, the vitelline duct fuses and degrades.
ileal diverticulum (Meckel’s) is just not completely degraded and only present in 2-3% of population and asymptomatic unless is enflamed and presents like appendicitis.
More serious ones…
Fibrous cord: there is fusion of the duct but it doesn’t disappear. It tethers the GI tract to the wall and can become twisted on itself.
Vitelline sinus: there is fusion proximally but there is an opening in the wall because the distal part doesn’t and can communicate with external environment.
Vitelline cyst: somewhere in the middle of the duct doesn’t fuse
Vitelline fistula - open communication with the gut tube and outside environment, fecal material can escape the umbilicus through this passage.
List the members of the foregut, midgut and hindgut
Along with blood supplies that branch off the aorta which is covered by the parietal peritoneum.
Foregut-Celiac trunk artery
- Esophagus
- Stomach
- Duodenum (celiac)
Collateral circulation
Midgut - Superior mesenteric artery
- Duodenum (superior mesenteric)
- Jejunum
- Ileum
- Cecum
- Appendix
- Ascending colon
- Transverse colon (superior mesenteric)
Hindgut - Inferior mesenteric artery
- Transverse colon (inferior mesenteric)
- Descending colon
- Sigmoid colon
- Rectum
- Anal canal
Describe the development of the liver + gallbladder
It starts as an evagination of the gut tube at the level of the 2nd duodenum known as the hepatic diverticulum going into the ventral mesentary.
The distal part of the endoderm will form the liver and gallbladder so it expands and the mesentary expands with it to become known as the visceral peritoneum.
The lesser omentum connects the gut tube to the developing liver and contains the common bile duct along with the vessels
The common bile duct splits into the cystic duct - gallbladder
And the common hepatic duct - liver
The falciform ligament connects the liver to the ventral abdominal wall.
Describe development of the pancreas.
What is a condition in abnormal development?
It is also at the level of the 2nd duodenum.
There are two outpocketing into both the ventral and dorsal mesentary as (pancreatic buds) However the ventral mesentary gets degraded so it must move.
Ventral pancreas bud moves dorsal, slightly more distal to the dorsal pancreas bud. They are both connected to the gut tube at the dorsal and ventral pancreatic ducts. The buds fuse.
The difference is that the ventral pancreas is connected to the common bile duct so it drags with it.
After fusion, the minor pancreatic duct (connected to the dorsal pancreas) is smaller than the major pancreatic duct (connected to ventral pancreas) for the reason that it also contains the common bile duct.
Abnormality - the ventral pancreas bud splits in two and both goes in different directions dorsally. This surrounds the secondary portion of the duodenum in pancreatic tissue known as ANULAR PANCREAS and this can compress the duodenum. Since it is right under the stomach, the stomach can’t be emptied fast enough and vomiting occurs.
In the fused pancreas, the ventral portion is the head of the pancreas,
Neck body and tail is the dorsal pancreas.
Describe the formation of the spleen.
It forms in the dorsal mesogastrium and isn’t an outpocketing.
Mesoderm cells are peeling away from the mesogastrium and aggregating together to form the organ between the dorsal mesogastrium to form the spleen.
The spleen gets bigger and the layers expand. At that point it’s the visceral peritonium of the spleen.
The aorta branches off artery to the spleen known as the splenic artery. The connection between the spleen and the dorsal body wall is the splenorenal ligament.
The connection between the stomach and the spleen was the gastrosplenic ligament.
There is no duct because its not an evagination.
What is ligamentum teres
It is the only vessel to transverse the ventral mesentary and is a remnant of the umbilical vein which allowed only a specific part of the ventral mesentary to survive.
It is in the falciform ligament.
Which organs can be referred as major secondary retroperitoneal organs?
PS: secondary retroperitoneal organs are always in front of primary secondary retroperitoneal organs.
That means they were peritoneal organs and is a result of the visceral peritonium fusing with the parietal peritonium and the visceral peritonium becomes known as parietal peritoneum and the vessles within the dorsal mesentary is renamed secondarily retroperitoneal.
Organs:
- Spleen
- Most of duodenum
- Most of pancreas
- Ascending colon
- Descending colon
- Upper rectum
The region of the fusion between the mesentary/visceral peritonium and parietal peritonium used to be peritoneal cavity so there is nothing there so it is known as the WHITE LINE OF TOLDT (avascular)
Describe foregut rotations.
The axis rotation is the long axis of the gut tube and it is a 90 degree rotation, ventral moves to the right side and the dorsal moves to the left side.
Liver is on the right side of the body and the spleen is on the left side of the body.
Most of the dorsal mesogastrium will fuse with the parietal peritoneum giving the appearance that the connection of the spleen is directly to the kidneys after rotation. This is why it is called the splenorenal ligament.
The lesser omentum at the level of the spleen does not include the liver. It is the superior free edge of the lesser omentum.
So on the right side there is a little space connecting the greater and lesser sacs. This is known as the EPIPLOIC FORAMEN OF WINSLOW.
Describe the midgut rotation.
Its the anterior posterior axis of the superior mesenteric artery into the midgut.
So during development, the abdomen is not growing fast enough the accomodate the elongating midgut so the midgut forms a loop into the umbilical cord and carries the superior mesenteric artery with it.
So imagine with me…
The jejunum is proximal (so superior)
Ileum/cecum/appendix is distal (so inferior), You are facing the stomach and it rotates 90 degrees counterclockwise from your perception. Then another 180 degrees. The jejunum will be on your right but the patient’s left. Ilium/cecum/appendix will be on the right.
The colon is dragged up the right side, across (transverse) and down (descending colon)
Describe the positions of organs regards to right and left and rotation. .
Right - ileum, ascending colon, liver
Left - jejunum, descending colon, spleen
What are the major primary and secondary retroperitoneal organs.
Primary:
- kidneys + adrenal glands
- ureter
- lower rectum
- aorta
- inferior vena cava
Secondary:
- most of duodenum
- Ascending colon
- Descending colon
- Upper rectum
- most of pancreas
What is the triad in the lesser omentum?
- Bile duct to the right
- Proper hepatic artery to the left
- Portal vein behind both of them
What is an omphalocele?
During development of the fetus, the midgut grows longer much faster than the abdomen grows large enough to accomodate it.
The midgut will go into the umbilical cord (do its 270 degree rotation around the superior mesenteric artery) and when the abdomen is large enough, it will retract.
If it doesn’t retract, it forms an omphalocele, small bowel will be in the umbilical cord.
What are astresias?
It is when the epithelial plugs are not vacuolized so a segment of the gut tube doesn’t have a lumen (most commonly in the duodenum)
Esophageal atresia results in inability to swallow amniotic fluid resulting in abd=normally high volume of amniotic fluid (polyhydramnios)
