GI development pt 1 Flashcards
What is the key stage which forms the ventral body wall and gets the gut within a cavity?
• Embryonic folding
What happens when the embryo folds laterally?
- Creates ventral body wall
* Primitive gut becomes tubular
What happens when the embryo folds cranicaudally?
• Creates cranial a caudal pockets from yolk sac endoderm (beginning of primitive gut development)
What are the three embryonic divisions of the gut?
- Foregut
- Midgut
- Hindgut
What does the division of the regions of the foregut determine?
• It’s blood and nerve supply
Where is only opening in the developing embryo?
• Mid gut
How do the divisions of the gut tube help us?
• Gives us structures for blood supply and lymphatic drainage in the adult
What is the stomatodeum?
• Future mouth
What is the proctodeum?
• Future anus
What is the opening into the yolk sac?
Vitelline duct
What is the internal lining of the gut derived from?
• Endoderm
What is the external lining of the gut derived from? What does it become?
• Splanchnic mesoderm
○ Future musculature
○ Visceral peritoneum
Where is the primitive gut tube found?
• In intraembryonic coelom, suspended by a double layer of splanchnic mesoderm
Give 7 structures found in foregut
- Oesophagus
- Stomach
- Foregut
- Pancreas,liver&gallbladder
- Duodenum(proximaltoentranceofbileduct)
What is the blood supply of the foregut?
• Celiac trunk
Give 6 structures found in midgut
- Duodenum(distaltoentranceofbileduct)
- Jejunum
- Midgut
- Ileum
- Cecum
- Ascendingcolon
- Proximal 2/3 transverse colon
What is the blood supply of the midgut?
- Superior Mesenteric Artery
* Superior Mesenteric Vein
Give 7 structures found in hindgut
- Distal1/3transversecolon
- Hindgut
- Descendingcolon
- Sigmoidcolon
- Rectum
- Upperanalcanal
- Internalliningofbladder&urethra
What is the blood supply of the hindgut?
- Inferior Mesenteric Artery
* Inferior Mesenteric Vein
Why is embryonic distinction important in terms of arterial blood supply?
• Each segment receives blood supply from a distinct branch of the abdominal aorta
What structures receive a mixed blood supply?
• Those which develop close to the junction between foregut and midgut
○ Duodenum
§ Proximal to entry of bile duct - Gastroduodenal & superior pancreaticoduodenal artery
§ Distal to entry of bile duct - Inferior pancreatic duodenal artery (SMA)
○ Pancreas
§ Head - Superior pancreaticoduodenal artery (CT)
§ Inferior pancreaticduodenal artery (SMA)
What are the most important arterial trunks for the GI tract?
- The celiac trunk
- The superior mesenteric artery
- Abdominal aota
- Inferior mesenteric artery
How is the intraembryonic coelom divided?
- By the diaphragm into abdominal and thoracic cavities
* Peritoneum and peritoneal cavity
What is the mesoderm of the gut split into?
- Somatic mesoderm
* Splanchnic mesoderm
What is the primitive gut surrounded by?
• Coelomic cavity
How is the abdominal wall formed?
- Two sides of the anterlateral wall meet in the linea alba
* One opening is left, at the umbilicus
What makes up the three layers of the anterolateral abdominal wall?
- The external oblique
- The internal oblique
- The transversus abdominis
What muscle is located on the anterior aspect of the abdominal wall?
• Rectus abdominis
What structure is deep to all of the muscles of the abdominal wall?
The transversalis fascia
What lines the external surface of the abdominal wall?
• The superficial fascia
What do the muscles and fascia of the abdominal wall develop from?
• Somatic mesoderm
What is the inguinal canal?
• An oblique passage through the layers of the abdominal wall
What does the inguinal canal allow in males?
• Allows the passage of the developing testis into the scrotum
What is a common condition in the inguinal canal?
Hernia
What is found in the inguinal canal in women?
• The round ligament of the uterus and the iliinguinal nerve
What is found in the inguinal canal in males?
• The spermatic cord and the iliinguinal nerve
What is an umbilical hernia?
• A congenital malformation where the intestines protrude through the abdominal wall
Why is umbilical hernia common in babies?
- Gut forms outside of the abdomen and later returns through an opening which becomes the umbilicus
- Abdominal contents can thus push against it and herniate outwards
What is an inguinal hernia?
• Inguinal canal a potential site of weakness through which the layers of the abdominal wall can herniate through
What is the coelomic cavity formed between?
• The somatic and splanchnic mesoderm
What is the intraembryonic coleom later subdivided by?
• The future diaphragm
What does the peritoneal membrane do?
• Lines the abdominal cavity and invests the viscera
Describe the attachments of the developing gut
- Attached to the roof of the abdominal cavity by the dorsal
- Attach to floor by the ventral mesentery
What do the dorsal and ventral mesentery become?
• Various peritoneal folds and reflections that suspend gut and give passage to vessels and nerves in the adult
What is the peritoneal membrane?
• Lines abdominal cavity and wraps around the viscera
What is the peritoneal cavity?
• A potential space, which contains nothing under normal conditions
What is a mesentery?
• A double layer of peritoneum suspending the gut tube from the abdominal wall
What is the purpose of a mesentery?
- Allow a conduit for blood and nerve supply
* Allow mobility where needed
What do the dorsal and ventral mesenteries divide the foregut into?
• Left and right sac
What does the left sac contribute to?
• The greater peritoneal sac
What does the right sac contribute to?
• The lesser peritoneal sac
Where is dorsal mesentery present?
• All the way along the gut wall
Where is the ventral mesentery found?
• Only in the foregut
What are the greater and lesser peritoneal sacs?
• Formed by the dorsal and ventral mesenteries, which divide foregut cavity into left and right
What are the omenta?
• Specialised regions of peritoneum
What is the greater omentum?
- Formed from the dorsal mesentery
* First structure seen when the abdominal cavity is opened anteriorly
What does the greater omentum connect?
• The greater curve of the stomach to the transverse colon
What does the lesser omentum connect?
• The lesser curve of the stomach to the liver
What is the lesser omentum?
- Formed from the ventral mesentery
* Free edge conducts the portal triad
How are the greater and lesser sacs formed, and how are the omenta formed?
• Rotation of the stomach
How does the primitive stomach rotate?
- Around the longitudinal axis
* Around the enteroposterior axis
What does rotation of the stomach cause? (6)
- Putsthevagusnervesanteriorandposteriortothestomachinsteadofleftandright
- Shiftscardiaandpylorusfromthemidline - stomach lies obliquely
- Contributestomovingthelesser sacbehindthestomach
- Createsthe greateromentum
- Original left side anterior
- Original right side becomes posterior
What is the peritoneal reflection?
• A change in direction
○ From parietal peritoneum to mesentery
○ From mesentery to visceral peritoneum
Where does the foregut extend to and from?
• The lung bud to the liver bud
What parts of the GI tract continue to possess mesenteries and why?
• The jejunum and ileum remain suspended from the posterior abdominal wall
What is retroperitoneal?
• Were never in the peritoneal cavity and never had a mesentery
What does secondarily retroperitoneal mean?
• Began development surrounded by peritoneum and had a mesentery, but mesentery is lost over time through fusion at posterior abdominal wall
What happens to the duodenum during development to make it retroperitoneal?
The duodenum and its mesentery is pushed against the posterior abdominal wall during development due to the rotation of the stomach and the large size of the liver
What is fusion fascia?
• Peritoneum of posterior abdominal wall squished together with the duodenum and its mesentery
Why is it easy to remove fusion fascia?
• It is avascular
What is formed in the ventral wall of foregut at the junction with the pharyngeal gut in the 4th weak?
• A respiratory diverticulum
What can form from an abnormal positioning of the tracheoesophageal septum?
• Oesophageal abnormalities
What creates the greater curvature of the stomach?
• Faster growth of dorsal curvature
What does the respiratory diverticulum becomes ventrally and dorsally?
- Ventrally - Respiratory primordium
* Dorsally - Oesophagus
What are the respiratory primordium and the oesophagus divided by?
• The tracheoesophageal system
What organs (or organ parts) are formed in the ventral mesentery?
- Liver
- Biliary system
- Part of the pancreas
What organs are formed in the dorsal mesentery?
Pancreas
What does the liver develop from?
• The hepatic bud within the ventral mesentery
What happens to the lumen of the duodenum?
- It is obliterated due to the lining growing so quickly
* Recanalised by the end of the embryonic period
What does the rotation of the stomach do to the duodenum?
• Pushes it right and then back again against the posterior abdominal wall
Dilation of what indicates stomach primordium?
• Distal foregut
What does rotation of the stomach and changing of the positions of the dorsal and ventral mesenteries form?
- Omental bursa formed
* Lesser sac displaced posteriorly from right
In terms of glandular development, where is the liver, biliary system and uncinate process and inferior head of pancreas formed?
• In the ventral mesentery
What is formed in the dorsal mesentery?
• Pancreas (superior head, neck body and tail)
What does the duodenum develop from?
- Caudal foregut
* Cranial midgut
How does the duodenum grow?
• Rapidly, forming a C-shaped loop when the stomach rotates
How does the lumen of the duodenum develop?
- In 5th and 6th week lumen is obliterated, then recanlised by the end of the embryonic period
- Rotation of the stomach pushes duodenum to right, then against posterior abdominal wall
Define secondarily retroperitoneal
•Astructurethatdevelopedintraperitoneally whosemesenterywaslosttofusionwithposteriorabdominalwallparietalperitoneumduetomassive massiveexpansion expansionofGItractduringdevelopment
