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GI-1,2 Introduction and Overview, Embryo crc
Pancreas. Produces HCO3-
What portion of the GI tract is important for neutralizing stomach acid?
Glycogen, vitamin B12, vitamin A
The liver is important for storing what?
Remove gut-derived bacteria from the blood
What does the liver clear from the blood?
Removes last bit of extra water
Stores residual stool until convenient to discharge
Prevents bacterial and parasitic invasion.
Why is the colon important?
Stomach, liver, pancreas, duodenum
What is the top circle, and what does it supply?
Small bowel, proximal colon
What is the middle circle, and what does it supply?
What is the bottom circle, and what does it supply?
How is the portal venous system connected to the systemic venous system?
Endoderm-lined yolk sac folds into embryo at wk 4.
When does the gut form, and from what?
What connects the primitive gut to the yolk sac?
What supplies the foregut?
Superior mesenteric artery
What supplies the midgut?
Inferior mesenteric artery
What supplies the hindgut?
What portion of the gut only gives rise to gut (not other organs)?
Gut epthelium, glands
What gut structures are derived from the endoderm?
Undifferentiated endodermal cells proliferate and occlude gut lumen
Then it recanalizes over the next 2 weeks
Definitive mucosal epithelium differentiates by week 9.
What happens to gut development at week 6?
Abnormal recanalization of the gut lumen following occlusion. This usually happens at the level of the duodenum
Duodenal atresia may be due to what?
Abnormal recanalization of the gut lumen following occlusion.
Intestinal duplication may be due to what?
Splanchnic mesoderm (from lateral mesoderm) gives rise to muscularis, lamina propria, submucosa, vessels, connective tissue
How does the mesoderm contribute to the gut?
Week 10, after the innervation of gut smooth muscle begins.
When does peristalsis begin?
Neural crest cells
What gives rise to the enteric ganglia, and what are the enteric ganglia?
What happens if the innervation of the gut does not happen correctly?
Liver, biliary tree
What structures are derived from the foregut?
4th week, off of the caudal foregut endoderm.
When do the liver, biliary, tree, pancreas arise from the ventral buds, and off of what?
Septum transversum (mesoderm between the heart and the midgut)
What does the hepatic diverticum grow into?
Endoderm-derived hepatocytes, biliary tree.
Mesoderm-derived connective tissue, hematopoietic, and Kupffer cells
What does the cranial part of the hepatic diverticulum grow into?
What is the major hematopoietic organ of the embryo?
The stalk that connects liverbud to duodenum becomes common bile duct.
The caudal and proximal parts of the hepatic diverticulum become what?
From dorsal and ventral buds
Ventral bud moves dorsally and the two buds fuse
How does the pancreas form?
What germ layer contributes to pancreatic acinar and islet tissue?
Early fetal peroid
When does insulin secretion begin?
Upper part of the head
Contributes to the accessory duct (of Santorini)
Dorsal bud of the pancreas gives rise to what structures of the pancreas?
Lower part of the head, uncinate process (lower left portion of head)
Main duct (Wirsung)
Ventral bud of the pancreas gives rise to what structures of the pancreas?
Like a napkin ring of pancreas surrounding the duodenum.
Result of bilobed ventral buds that rotate dorsally on both sides of duodenum and fuse with dorsal bud
Can cause duodenal obstruction, pancreatitis, peptic ulcer.
What is an annular pancreas?
Small intestine from distal duodenum
Ascending and proximal transverse colon
What portions of the GI system do the midgut give rise to?
Not known for sure, but perhaps because hematopoietic liver is so huge that there is simply no room.
Why does the midgut under umbilical herniation at week six?
Attached to yolk sac via yolk stalk (vitelline duct)
What is attached to the leading edge of the herniating midgut?
At week six, midgut herniates in U-shaped "primary intestinal loop" into the cord.
When does the midgut undergo herniation?
Duodenal obstruction, peptic ulcer disease, pancreatitis
What diseases is this process associated with?
At week six, midgut herniates in U-shaped "primary intestinal loop" into the cord. Loop attaches to the yolk sac via vitelline duct.
When out in the cord, gut rotates 90 degrees CCW
What is happening here?
What happens right afterward?
From weeks six to 10-11.
During what weeks is the midgut herniated into the umbilicus?
Week 10-11. When it returns, it rotates another 180 degrees CCW.
When does the midgut return to the abdomen after herniation?
This is unclear.
Why does the gut return to the abdomen?
What happens if the gut doesnt return to the abdomen?
You get something called "nonrotation," in which there is small bowel on the right side and colon on the left.
This increases the risk of volvulus and obstruction
What happens if the gut doesn't rotate?
90 degrees CCW while herniated
180 degrees CCW right after herniation
How much does the gut rotate during development?
What happens if the omphalomesenteric (vitelline) duct persists?
Omphalocele, in that the herniated midgut did not return to the abdomen
What is happening here in this ultrasound?
Omphalocele in a term baby
Small bowel on the right and colon on the left
Increased risk of volvulus and obstruction.
What sort of bowel distribution is there in a case of failure of gut rotation?
Gut twists and cuts of blood supply, usually resulting in a red infarct
What happens in the case of volvulus?
Volvulus resulting in a red infarct and then necrotic, dead bowel.. This can occur especially in a "nonrotated" gut.
Abnormal persistence of the vitelline (omphalomesteric) duct leads to Meckel's diverticulum
What happens if the circled structure here persists?
Meckel's diverticulum, due to abnormal persistence of the vitelline duct (omphalomesteric duct). This can be connected to the umbilicus via a fibrous cord.
This is a section of midgut at the level of the ileum. What might this be, and what created this?
Where in the gut does a Meckel's diverticulum occur?
Distal transverse colon
Descending sigmoid colon
Superior anal canal
Lining of urinary bladder
Most of the urethra
What does the hindgut give rise to?
Portion of the endoderm of the cloaca that is in contact with the ectoderm. Otherwise, the cloaca is divided from the ectoderm by mesoderm.
(Thin light pink area in the diagram)
What is the cloacal membrane?
Urorectal septum, a wedge of mesoderm that will divide cloaca into rectum and bladder
What will divide the cloaca into what?
Contribute small porttion of endoderm to bladder
Lumen disappears, becomes fibrotic cord, forms urachus (median umbilical ligament)
What structures are derived from the allantois?
Urine leakage from umbilicus
Urinary tract infection
What are some complications of a failure of the urachus lumen to obliterate?
If the lumen of the median umbilical ligament fails to obliterate, what kind of structures can you have?
Tourneaux and Rathke folds
Tourneaux comes in from median, while Rathke come in from the sides.
What folds are included in the urorectal septum?
Divided by urorectal septum into two parts: urogenital membrane and the anal membrane
What eventually happens to the cloacal membrane?
Mesoderm around anal membrane proliferates, creating the proctoderm (anal pit). This gives rise to the anal pit. The anal membrane breaks down around week 8
What eventually happens to the anal membrane?
If anal membrane fails to break down, or if urorectal septum position is abnormal.
What might give rise to an imperforate anus?
Imperforate anus, due to either a failure of the anal membrane to break down, or if the urorectal septum position is abnormal.
Pretty much right where the anal membrane was, i.e. where the junction was between endoderm and ectoderm.
Embryological origin of the pectinate line?
Microscopic view of the pectinate line. Area of irregular mucosal folding in anorectal canal.
What is this?
Inferior mesenteric artery
Blood supply above pectinate line?
Internal iliac artery
Blood supply below pectinate line?
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