Lecture 3 - GI Development Flashcards
When does the embryo fold
4th week
Embryonic folding
Laterally
- creates ventral wall
- primitive gut becomes tubular
Craniocaudally
- creates cranial and caudal pockets from yolk sac endoderm
- beginning of primitive gut development
Gut tube
Endoderm lined tube covered by splanchnic mesoderm
Runs the length of the body
Blind ended caudocephalically
Opening at the umbilicus
Splanchnic mesoderm innervation and implication
Innervation by the visceral nervous system
- parasympathetic and sympathetic innervation
Therefore non localised pain
Derivatives of the foregut
Oesophagus
Stomach
Pancreas, liver and gall bladder
Duodenum - proximal to the entrance of the bile duct (at sphincter of Oddi)
Midgut derivatives
Duodenum Jejunum Ileum Caecum Ascending colon Proximal 2/3rds of the transverse colon
Hind gut derivatives
Distal 1/3rd of transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of bladder and urethra
Foregut blood supply
Coeliac trunk
Midgut blood supply
Superior mesenteric artery
Hindgut blood supply
Inferior mesenteric artery
Duodenal blood supply
Proximal to sphincter of oddi:
Gastroduodenal artery and superior pancreaticoduodenal artery from the coeliac trunk
Distal to sphincter of Oddi:
Inferior pancreaticoduodenal artery from the superior mesenteric artery
Pancreas blood supply
Superior and inferior pancreaticoduodenal artery from the coeliac trunk and superior mesenteric artery
Intraembryonic coelom
One large cavity formed during embryonic folding
The diaphragm splits the coelom into abdominal and thoracic cavities
Septum transversum
Indicates where the diaphragm will develop and separates the abdominal and thoracic cavities
Mesentery
Double layer of peritoneum suspending the gut tube from the abdominal wall
- allows mobility
- allows a conduit for blood vessels and nerves
What does the dorsal mesentery cover
Entire gut tube
What does the ventral mesentery cover
Foregut
Greater and lesser peritoneal sacs
In the foregut, the dorsal and ventral mesentery divides the cavity into left and right sacs
Left sac = greater sac
Right sac = lesser sac (behind stomach)
Omenta
Specialised regions of peritoneum
Greater omentum
Formed from the dorsal mesentery
Lesser omentum
Formed from the ventral mesentery
Free edge is a conduit for the portal triad
Connects the liver and lesser curve of stomach
Consequences of the rotation of the stomach
- Vague nerves move anterior and posterior to the stomach instead of left and right
- liver moves to the right of the stomach
- spleen moves to the left of the stomach
- shifts cardia and pylorus from the midline
- stomach lies obliquely
- formation of lesser sac and greater omentum
Peritoneal reflection
Change in direction of peritoneum I.e.
- parietal to mesentery
- mesentery to visceral
- visceral to parietal
Retroperitoneal
Never in the peritoneal cavity and never had a mesentery
Behind peritoneum
Secondarily retroperitoneal
Began development invested in the peritoneal cavity and had a mesentery but during development, lost its mesentery as it fuses with the posterior abdominal wall
E.g. duodenum and pancreas
Where does the foregut extend from?
From the lung bud to the liver bud
GI tract development
In the 4th week, a respiratory diverticula forms in the ventral wall of the foregut at the junction with the pharyngeal gut
- respiratory primordial - ventral
- oesophagus - dorsal
Abnormal positioning of the tracheaoesophageal septum
- proximal blind ended oesophagus
- tracheoesophageal fistula
Where does the liver and biliary system develop from
Ventral mesentery
Where does the pancreas develop from?
Uncinate process and inferior head = ventral mesentery (duct system)
Superior head, neck, body and tail = dorsal mesentery (gland portion)
Falciform ligament
Connects the liver to the abdominal chest wall
Duodenum development
Develops from the caudal foregut and cranial midgut
Shape is due to stomach rotation as pushed to the right and against posterior abdominal wall
Secondarily retroperitoneal
What creates the greater curvature of the stomach
Faster growth of the dorsal border
Where is the midgut connected to the yolk sac?
Midpoint of the midgut
Physiological herniation
The midgut grows faster than the abdominal cavity so by week 6, it protrudes through the abs minimal wall into the umbilical cord
Midgut rotation
Midgut rotates 90 degrees whilst in the umbilical cord
In total the midgut rotates 3x of 90 degrees
Umbilical hernia
If an abnormally large opening between the abdominal cavity and umbilical cord persists, an umbilical hernia can occur at birth
