11- Development of GI System Flashcards
During the 4th week, embryonic folding pulls the endoderm of the yolk sac into the cranial and caudal ends of the embryo forming the ________, ________, and _______ with narrow opening to yolk sac forming the ________ _______ (yolk stalk).
Foregut
Midgut
Hindgut
Vitelline Duct
The gut tube is closed on both ends by the __________ (cranial) and ________ ________ (caudal). Here, the endoderm and ectoderm are in direct contact with one another.
Buccopharyngeal
Cloacal Membranes
What portion of the primordial gut forms the following?
- Oral Cavity
- Pharynx
- Lower respiratory tract
- Esophagus
- Stomach
- Liver
- Gallbladder
- Pancreas
- Upper Duodenum (proximal to bile duct)
Foregut
***Just remember mouth to upper duodenum is foregut!
What is the arterial supply to the foregut structures below the diaphragm?
Celiac Trunk
What portion of the primordial gut forms the following?
- Lower Duodenum
- Jejunum
- Ileum
- Cecum
- Appendix
- Ascending Colon
- Proximal 2/3 of Transverse Colon
Midgut
What is the arterial supply to the midgut structures?
Superior Mesenteric A. (SMA)
What portion of the primordial gut forms the following?
- Distal 1/3 of Transverse Colon
- Descending Colon
- Sigmoid Colon
- Rectum
- Upper Anal Canal
Hindgut
What is the arterial supply to the hindgut structures?
Inferior Mesenteric A. (IMA)
This germ layer forms the epithelial lining and associated glands of the GI tract (except for lower 1/3 anus).
Endoderm
This germ layer generates CT, vasculature, and smooth muscle walls.
Splanchnic Mesoderm
This germ layer forms the enteric ganglia, nerves, and glia of the GI tract (via NCCs) as well as the epithelium of lower 1/3 of the anus.
Ectoderm
Maturation of the GI gastroepithelium is well underway by ________ weeks and peristaltic contractions begin as early as week ________.
8-10
10
By the end of the 4th week, the gut tube caudal to the developing diaphragm is suspended from the posterior abdominal wall by a _________ _________. This extends from the lower esophagus to the caudal end of the hindgut.
Dorsal Mesentery
What are the adult derivatives of the dorsal mesentery?
– Greater Omentum (forming Gastrosplenic, Gastrocolic, and Splenorenal Ligaments)
– Small intestine mesentery
– Mesoappendix
– Transverse mesocolon
– Sigmoid mesocolon
This is the term for a double fold of peritoneum.
Mesentery
A ________ ________ develops between the ventral body wall and the foregut running from the septum transversum and stomach to the umbilicus.
Ventral Mesentery
What are the adult derivatives of the ventral mesentery?
– Lesser Omentum (forming Hepatoduodenal and Hepatogastric Ligaments)
– Falciform Ligament of Liver
– Coronary Ligament of Liver
– Triangular Ligaments of Liver
__________ organs are suspended by a mesentery, while __________ organs are those organs excluded from the peritoneal cavity.
Intraperitoneal
Retroperitoneal
_________ _________ organs were initially suspended within the mesentery but later in development become fused with the body wall. These include the ascending and descending colon, duodenum, and bulk of the pancreas.
Secondarily Retroperitoneal
While suspended by both ventral and dorsal mesenteries, the developing stomach elongates and rotates…
90 degrees
In the rotation of the stomach, the left stomach surface becomes (VENTRAL/DORSAL) and the right stomach surface becomes (VENTRAL/DORSAL).
Ventral
Dorsal
***Ventral border of stomach moves to the right, and dorsal border of stomach moves to the left!
The portion of the dorsal mesentery between the body wall and stomach is referred to as the ________ ________. As the stomach enlarges and rotates, this also enlarges forming a large draping double-fold of mesentery that eventually anteriorly overlies the lower abdominal contents forming the ________ ________.
Dorsal Mesogastrium
Greater Omentum
The stomach rotation also divides the abdominal cavity into a _______ _______ lying behind the stomach, and a ________ ________ laying anteriorly and continuous with the greater abdominal cavity.
Lesser Sac
Greater Sac
Rotation of the stomach also changes the orientation of the right and left vagus nerves to one consisting of anterior/posterior vagal trunks. Which vagus nerves form which vagal trunks?
Left Vagus N. = Anterior Vagal Trunk (ventral stomach)
Right Vagus N. = Posterior Vagal Trunk (dorsal stomach)
This defect in stomach development has an incidence of 1:500. There is a narrowing of pyloric lumen thereby obstructing food passage. There’s an inability of the sphincter to relax due to faulty NCC migration so ganglion cells of ENS are not properly populated.
Hypertrophic Pyloric Stenosis
In Hypertrophic Pyloric Stenosis, the muscularis externa in the region hypertrophies forming a palpable mass (“olive”) at the _______ _______ _______.
Right Costal Margin
T/F. Hypertrophic Pyloric Stenosis is associated with projectile non-bilious vomiting after feeding, fewer and smaller stools, and an excess gain in weight.
False. Hypertrophic Pyloric Stenosis is associated with projectile non-bilious vomiting after feeding, fewer and smaller stools, and failure to gain weight (may actually lose weight).
The liver begins as _________ from gut endoderm that grows into the septum transversum (liver not derived from septum transversum, just dependent on signals from it).
Diverticulum
Endoderm of the liver differentiates into what?
Hepatocytes
Bile Ducts
Hepatic Ducts
***Bile formation by hepatic cells begins week 12!
Splanchnic mesoderm of the liver differentiates into what?
Stromal Cells
Kupffer Cells
Stellate Cells
The liver functions as an embryonic _________ organ. Congenital anomalies of the liver are very rare.
Hematopoietic
In pancreas formation, endodermal buds sprout into the…
Dorsal and Ventral Mesenteries
In pancreas formation, what grows into the Ventral Mesentery and the Dorsal Mesentery?
Cystic Diverticulum and Ventral Pancreatic Bud grow into Ventral Mesentery.
Dorsal Pancreatic Bud grows into Dorsal Mesentery.
The pancreatic buds develop both ________ and ________ portions.
Exocrine
Endocrine
During the 5th week, the ventral pancreas migrates around posteriorly and fuses with the dorsal pancreas. What does the ventral pancreas and dorsal pancreas form?
Ventral Pancreas = Forms Uncinate Process
Dorsal Pancreas = Forms head, body, and tail
The Dorsal Pancreatic Duct connection to the duodenum is lost as it reconnects to the Ventral Pancreatic Duct. However, it may be retained as the…
Accessory Pancreatic Duct
***This is an anomaly that occurs in 33% of people!
This pancreatic anomaly is when a person has two totally separate ducts. Patients are prone to pancreatitis. Occurs in 4% of people.
Pancreas Divisum
This pancreatic anomaly is due to duodenal obstruction or stenosis. Bilious vomiting can occur if the annulus develops inferior to the bile duct. Born with low birth weight and occurs in 1:12,000-15,000.
Annular Pancreas
The gallbladder and bile ducts are formed by outgrowths from ________ ________. The bile duct is initially closed but opens via canalization.
Cystic Endoderm
In this anomaly, there are fetal and perinatal forms. It is defined as the obliteration of extrahepatic and/or intrahepatic ducts. The ducts are replaced by fibrotic tissues due to acute or chronic inflammation.
Biliary Atresia
What bile duct anomaly is being described by the following systems?
- Progressive neonatal jaundice with onset soon after birth
- White clay colored stool
- Dark colored urine
- 12-19 month average survival time
- Can be treated with liver transplant
Biliary Atresia
During the 4th week, a mesenchymal condensation develops in dorsal mesogastrium and is the site of _______ formation.
Spleen
Spleen is derived from _________ and will be eventually populated by _______ _______ cells.
Mesoderm
Myeloid Lymphoid Cells
Because of the limited size of the abdomen, the lengthening midgut loop has to do what?
Hernia out into the umbilicus (6 weeks) and be brought back in (10 weeks)
Explain what happens in the first 90 degree rotation of the gut.
There is a 90˚ CCW rotation at about 50 days, bringing the cecum and future ascending colon into the left side of the abdominal cavity.
Explain what happens in the second 180 degree rotation of the gut.
There is a second 180˚ CCW rotation at about 70 days as the gut loop is reentering the abdomen. It brings the cecum to the RUQ and the ascending colon anterior to the duodenum.
As the midgut returns into the cavity (at about 73 days), the cecum descends to the ________ (at about 77 days) carrying the ascending colon along with it so the ascending colon ends up along the ________ side of the abdomen and the _______ _______ overlies the duodenum and pancreas.
RLQ
Right
Transverse Colon
This is the term for when herniation of the gut into the umbilicus remains and is still covered by peritoneum. There is increased risk of this seen with trisomy 13 and 18. Occurs in 2.5 in 10,000 births.
Omphalocele
What are the possible etiologies of Omphalocele?
– Herniated bowel just does not fully retract
– Lateral body folding and fusion is abnormal creating a wall weakness allowing the bowel to herniate
– CT of skin and hypaxial musculature of body wall do not form normally thereby creating a wall weakness
This is a herniation of abdominal contents through abdominal wall and into the exterior. There is no peritoneal covering. Occurs in 1:10,000.
Gastroschisis
This is due to the failure of the yolk stalk (vitelline duct) connection to the midgut to regress, so the midgut remains connected to the umbilicus. Can lead to abdominal swelling, intestinal obstruction, bowel sepsis, and GI bleeding.
Meckel’s Diverticulum
What is the “Rule of 2’s” for Meckel’s Diverticulum?
- 2% incidence
- 2X’s more common in males
- 2% have medical symptoms
- Usually 2 feet proximal to terminal ileum
- Usually 2 inches long
- Usually 2 years of age
This is the term for rolled up, twisted intestines. Symptoms include acute abdominal pain, vomiting, and GI bleeding. Increased risk with gut rotation anomalies.
Volvulus
This occurs when the gut completes the first 90˚ CCW rotation but does not do the remaining 180˚ CCW rotation. Ends up with left-sided colon and right-sided small intestines. Occurs in 1:500 births.
Non-Rotation of Midgut Loop
This occurs when the gut completes the first 90˚ CCW rotation but then does a 180˚ CW rotation (rather than CCW) resulting in a net 90˚ CW rotation. Now the Transverse Colon ends up posterior to the Duodenum.
Reverse Gut Rotation
During the 5th-6th month the lumen of the intestines become nearly completely obliterated due to endodermal proliferation and villi formation. Later, vacuoles form as endodermal cells degenerate. This reopens the lumen (canalization). ________ _______ is the partial occlusion of the duodenum due to ineffective recanalization, usually involving horizontal and/or ascending parts.
Duodenal Stenosis
________ ________ is the complete occlusion of the duodenal lumen. Commonly associated with trisomy 21.
Duodenal Atresia
The ________ ________ partitions the cloaca into a dorsal anorectal canal and a ventral urogenital sinus.
Urorectal Septum
The Urorectal Septum develops fork-like extensions (infoldings) of the lateral cloacal walls that grow toward one another, dividing the cloaca into _______ _______ and ________ ________.
Urogenital Sinus
Anal Canal
The ________ ________ ruptures, thereby opening both the Urogenital Sinus and Anal Canal to the exterior.
Cloacal Membrane
The anal rectal lumen is temporarily closed by epithelial…
Anal Plug
Mesenchyme surrounding the anal canal proliferates forming an _______ _______ with ectodermal lined walls.
Anal Pit
The anal plug eventually opens via _________ death.
Apoptotic
The superior 2/3s of the anal canal is the ________ and is composed of _________ epithelium.
Rectum
Endodermal
The rectum has a separate BV supply and innervation (hindgut). What provides the blood supply?
Superior and Middle Rectal arteries and veins
The inferior 1/3 of the anal canal is the ________ and is composed of _________ epithelium.
Anus
Ectodermal
The anus has a separate BV supply and innervation (anal pit). What provides the blood supply?
Inferior Rectal arteries and veins
This is the line that divides the origin of the hindgut and the anal pit.
Pectineal Line
This is the term for a persistent anal membrane. Various types are distinguished on whether they are low, intermediate, or high relative to the levator ani and pelvic landmarks. Occurs in 1:5000 births.
Imperforated Anus
This disease is due to the absence of ganglionic plexus due absence of migration of NCCs. There is an increased wall thickness due to hypertrophy in the intestine proximal to the aganglionic segment. Lack of peristalsis (colon fails to relax), and abnormal colonic dilation or distention (megacolon).
Hirschsprung’s Disease (Congenital Aganglionic Megacolon)
How can we treat Hirschsprung’s Disease?
Surgical removal of constricted distal segment of intestine
