Development of GI Tract Flashcards
Foregut blood supply
Celiac trunk
Midgut blood supply
SMA - superior mesentaric artery
Hindgut blood supply
IMA - inferior mesenteric artery
Narrowing of the opening to the yolk sac during embryonic folding creates?
Vitelline duct
What creates the mucosal epithelium and GI glands (minus lower 1/3 of anus)?
Endoderm
What creates the CT, vasculature and smooth muscle wall of GI tract?
Splanchic mesoderm
What creates the ganglia, nerves, glia, and epithelium of lower 1/3 of anus?
Ectoderm
What lines the peritoneal cavity?
Parietal peritoneum
What lines the abdominal organs?
Visceral peritoneum
Space between the parietal and visceral peritoneum?
Peritoneal cavity
Double fold of peritoneum that connects organs to body walls so they are not floating around aimlessly?
Mesentary
Connects organs to dorsal body wall and runs entire GI tract
Dorsal mesentary
Connects organs to ventral body wall and runs from ventral stomach to umbilicus
Ventral mesentary
What does the Dorsal mesentary give rise to?
Greater omentum Small intestine mesentary Mesoappendix Transverse mesocolon Sigmoid mesocolon
What does the Ventral mesentary give rise to?
ALL THINGS LIVER: Lesser omentum Falciform ligament of liver Coronary ligament of liver Triangular ligament of liver
Greater omentum includes?
Gastrosplenic, Gastrocolic and Splenorenal ligaments
Lesser omentum inlcudes?
Hepatoduodenal and Hepatogastric ligaments
Organs suspended by mesentary
Intraperitoneal
Organs excluded from peritoneal cavity
Retroperitoneal
What are the retroperitonal organs?
SADPUCKER: suprarenal glands aorta duodenum - 2nd and 3rd parts pancreas - except tail ureters colon - ascending and descending kidneys esophagus rectum
Organs initially suspended within mesentary that later fused with body wall
Secondarily retroperitoneal
Examples of secondarily retroperitoneal organs
Ascending and descending colon
Bulk of pancreas
Duodenum
What does the Foregut create?
Esophagus Stomach Liver Gallbladder Pancreas Upper duodenum
The stomach is suspended by both the dorsal and ventral mesentaries, describe its rotation
It elongates and rotates 90 degrees and takes vagus nerve and mesentaries with it, then the dorsal edge expands to make greater curvature
As the stomach rotates, the dorsal mesogastrium becomes?
Greater omentum
As the stomach rotates, the ventral mesentary becomes?
Lesser omentum
Once the stomach rotates, what is the alignment of the vagus nerve?
LARP
- left vagus anterior
- right vagus posterior
After stomach rotation, what is the greater sac?
Greater space of peritoneal cavity
After stomach rotation, what is the lesser sac?
Space behind the stomach
Faulty migration of NCC, inability of sphincter to relax
Hypertrophic pyloric stenosis
Hypertrophic pyloric stenosis
Narrowing of pyloric lumen (opening btwn stomach and duodenum) due to thickened muscle
- Presents after birth, palpable “olive” mass
- Non-bile vomit, lesser stools and loss of weight
Describe the liver formation
Begins as hepatic diverticulum from foregut endoderm via connection of common bile duct
- By 10th week in utero, takes over hematopoiesis
Endoderm liver cells
Hepatocytes, hepatic ducts and bile ducts
Mesoderm liver cells
Stromal, Kupffer and stellate cells
Describe the gallbladder formation
Begins as cystic diverticulum; a secondary outpouching off common bile duct and grows into ventral mesentary
Bile formed by hepatic cells beginning in week ___
12
The gallbladder is connected to the common bile duct what?
Cystic duct
Biliary Atresia
Obliteration of bile duct or it is replaced by fibrotic tissue
- Jaundice, white clay stool, dark urine
Describe the pancreas formation
2 buds (ventral and dorsal) sprout inferior to the cystic diverticulum on the foregut - Ventral bud migrates posteriorly and fuses with the Dorsal bud and duct
The ventral pancreatic bud creates
Uncinate process
The dorsal pancreatic bud creates
Pancreas head, body and tail
Main pancreatic duct?
Ventral
Accessory pancreatic duct?
Dorsal
Pancreas Divisum
Ventral and Dorsal pancreatic buds fail to fuse
- Mostly asymptomatic
Annular pancreas
Poor migration of ventral pancreas
- Creates a pancreatic ring around 2nd part of duodenum
- Can cause obstruction, bilious vomit and low birth weight
Where does the spleen form and what is it derived from?
It forms in the dorsal mesogastrium
It is derived from MESODERM
What does the midgut create?
Lower duodenum Jejunum Ileum Cecum Appendix Ascending colon Proximal 2/3 transverse colon
What is unique about the midgut formation?
It herniates out of umbilicus at week 6 and returns to abdomen at week 10
Describe the midgut formation between week 6-10
- Midgut grows out of umbilicus and makes a 90 degree counterclockwise turn so the proximal gut is on the right side
- Proximal side becomes convoluted and distal side forms cecum
- Proximal side returns to abdomen and passes under distal portion, completing another 90 degree turn
- Distal portion returns and makes a 3rd 90 degree turn
Herniated midgut does not fully retract like it is supposed to through umbilicus
- Covered by parietal peritoneum
Omphalocele
Abnormal lateral body folding/fusion - defect in abdominal wall causes wall weakness
- Bowel herniates out
- Not covered in parietal peritoneum
Gastroschisis
Failure of vitelline duct connect to midgut to regress
- Midgut remains connected to umbilicus
- Rule of 2’s
Meckel’s Diverticulum
- 2% population and symptoms
- 2x more likely in males
- presents in first 2 years of life
Midgut only rotates 90 degrees, end up with a left sided colon
Malrotation/non-rotation of midgut loop
Midgut rotates a NET 90 degrees CLOCKWISE, end up with duodenum anterior to transverse colon
Reverse gut rotation
Twisting of bowel around its mesentary
“coffee bean sign”
- abdominal pain, vomiting, bleeding
Volvulus
What does the Hindgut create?
Distal 1/3 transverse colon Descending colon Sigmoid colon Rectum Superior 2/3 anal canal
Portion of hindgut during development that separates into rectum and urogenital sinus
Cloaca
What develops fork-like extensions that grow inward to separate the cloaca?
Urorectal septum
The urorectal septum separates the cloaca into?
Urogenital sinus and anorectal canal
What ruptures to open the urogenital sinus and anorectal canal to the exterior?
Cloacal membrane
The urogenital sinus will eventually become what?
Bladder and urethra
Rectum is derived from what?
Endoderm
Anus is derived from what?
Ectoderm
What blocks the rectal lumen from the anal opening?
Anal plug that will eventually undergo apoptosis
____ surrounding anal opening proliferates outward to form _____
Mesoderm
Anal pit
The anal pit is lined with?
Ectoderm
What divides the origin of the hindgut and the anal pit?
Pectineal line
Pectineal line seperates the rectum and anus; thus seperating what type of origin derivation?
Endoderm (rectum) and Ectoderm (anus)
Imperforate anus
Opening to anus is missing or blocked due to persistent anal membrane
Abnormal urorectal septum
Urorectal septum does not properly separate the urogenital sinus and rectum
Hirschsprung’s Disease
Failure of NCC migration which causes absent ganglionic plexus; and then colon fails to relax
Signs seen with Hirschsprung’s Disease
Intestinal wall hypertrophy proximally
Abnormal colonic dilation
Failure to pass meconium
