Lecture 14: Embryology of the Gut Flashcards
What are the two foldings involved in primitive gut formation
Later folding and cephalo-caudal folding
What primary get layers makes up the gut?
Endoderm
What are structural derivatives of the ectoderm?
Skin and nervous system
What are structural derivatives of the mesoderm?
CT, cartilage, muscle, bone, and blood
What are the directions for the cephalic-caudal and lateral plate mesoderm folds?
Cepalo-caudal- inwards
Lateral plate mesoderm- lateral
both form the body wall and body because the head and tail region become distinct from one another
As these two folds in the embryo occur, a big space develops, what is that called?
Intraembryonic coelomic cavity
What are the 3 body cavities derived in the intraembryonic coelomic cavity in the adult
Pleural cavity, pericardial, peritioneal cavity
Compare the size of the embryo peritoneal cavity to the adult
Embryo is much larger than the adult due to the growth of the organs
Significant structures that arise from the folding of the lateral plate mesoderm in the adult
Visceral and parietal paritoneum
How is the primitive gut separated from the yolk sac
Lateral and cephalo-caudal folding
Will a connection between the yolk sac and the primitive gut still exist after folding? If so how?
Yes because the yolk stalk (vitaline duct or omphalomesenteric duct) remains connected but continues to narrow with time
What structures will become a part of the forgut?
Forms pharynx, esophagus, stomach, proximal half duodenum, liver, pancreas, gal bladder, lower respirtory system
What structures will become a part of the midgut
Forms distal duodeum, jejunum, illeum, large intestine up to proximal 2/3 of transverse colon
What is the midgut region connected to in the embryo
Yolk sac
What structures will become a part of the hindgut
Forms the lateral 1/3 of transverse colon, descending colon, sigmoid colon, rectum, gut part of anal canal
Allantois
Membrane that becomes incorporated into the embryo (in the hindgut region) and participates in the formation of the cloaca
How is the gut attaches to the back body wall?
Dorsal mesentery
Describe how the dorsal mesentery is formed
The cephalo-caudal and lateral foldings divides the mesoderm into the somatic (on the body) and splanchnic mesoderm (on the gut). The dorsal mesentery is a double layer fold of splanchnic mesoderm
Other than the dorsal mesentery, what else is derived from the splanchnic mesoderm?
Smooth muscle of GI tract
What organs are suspended by the dorsal mesentery
Every gut organs
What is the space between the somatic and splanchnic mesoderm called
Intraembryonic coelomic cavity
The ventral mesentery grows very early, what happens to the ventral mesentery when the liver begins to grow
The liver divides the mesentery into 2 parts- the falciform ligament and lesser omentum
What are two structural derivatives of the dorsal mesentery
Falciform ligament and lesser omentum
Where is the ventral mesentery present?
forgut (unlike dorsal mesentery)
What mesoderm derive the parietal and viscera paritoneum
Parietal- Somatic mesoderm
Visceral- Splanchnic mesoderm
What does the diaphragm separate
Thorax from abdomen
Describe the role of mesenchymal cells in diaphragm and ventral mesentery formation
There is a sheet of mesenchyme cells (undiff. cells) with a top and bottom
-top part forms the diaphragm and the bottom part forms the ventral mesentary.
How many different parts form the diaphragm
4
What are the different parts that form the diaphragm
- Septum transversum
- Pleuroperitoneal folds
- Mesentery of esophagus
- Skeletal muscle cells
What portion of the diaphragm does the septum transversum create?
The anteriolateral region of diaphragm including central tendon
Describe the movement of the septum transversum with spinal/vertebral cord levels
Initially lies opposite to Spinal cord levels C3,4, and 5 in the embryo then descents to vertebral level L1, taking the phrenic nerve with it
Does the septum transverse completely close of the thorax and abdomen
no
Role of the pleuroperitoneal folds
Close off the posteriolateral gaps in the diaphragm (called pericardioparitoneal canals)
Where do the pleuroperitoneal folds originate and where do they extend?
They originate from the caudal border of pleural cavities then grow to meet each other and the septum transversum
What entraps the dorsal mesentery of the esophagus
the pleuroperitoneal folds and septum transverse
What is another name for the dorsal mesentery of the esophagus
mesoesophagus
Where does the cura of the diaphragm develop
mesoesophagus
Where is most of the muscle on the diaphragm located
At there periphery
What is the embryonic derivative of the skeletal muscle in the diaphragm
mesenchymal cells
Where does all of the muscle on the diaphragm attach
Central tendon
How do Diaphragmatic hernias result?
Failure of closing the pleuorperitoneal folds
What’s the consequence of diaphragmatic hernias?
The pericardioperitoneal canals remain open, allowing abdominal visceral to move into the thorax interfering with lung maturation
What does the forgot form in the embryo
pharyngeal pouches, esophagus, trachea, lung buds, stomach, liver, bilary system, and pancreas
What is the blood supply for all forget organs
Celiac trunk
How does the esophagus develop?
Out pocketing of the respiratory or tracheobronchial divriticulum from its ventral wall
Why is out pocketing of the tracheobronchial divriticulum necessary
To ensure the completion of the esophagotracheal septum
What is the esophagotracheal septum
Separates the esophagus (pathway for food) from the trachea (pathway for air)
What is the last structure to form in the lungs
Alveoli (site of gas exchange)
How do the alveoli develop
The tracheobronchial divriticulum interacts with the mesoderm
Atrasia of esophagus
When the esophagus is not connected at the point where the esophagus is shut off from the trachea. Causing babies to spit up their food
Esophageotracheal fistula
The esophagus and trachea are not closed off from one another causing lots of gas to enter the stomach
Does the esophagus have a mesentary
Yes the dorsal mesentery of the esophagus or mesoesophagus
what structure develops in the dorsal mesentery of esophagus?
Diaphragmatic cura
What two mesenteries are contained within the stomach
The dorsal and ventral mesentery (called dorsal and ventral mesgastrum for stomach)
What is the ventral mesogastrum formed by
septum transversum
How is the mental bursa formed
In gut development- the rotation and uneven growth in the dorsal mesgastrum for the stomach to bend to the left making the mental bursa
How is the great omentum formed in embryonic development
The dorsal mesgastrum grows in the caudal direction as the stomach rotates along its anterior posterior axis to form greater omentum
Compare the great omentum in the embryo v.s the adult.
In the embryo the greater omentum is open to the mental bursa. In the adult the visceral layers of the greater omentum fuse and close off this connection (this occurs because the transverse colon is growing and pushes until the omental bursa is partially shut off)
What happens when the stomach rotates 90 degrees
Puts the left vagus n. on the anterior portion of the stomach and esophagus and the right vagus n. on the posterior esophagus and stomach (this is how it is in the adult)
What is the orientation of the 2 vagus nerves (left and right) on the embryonic gut?
They were on their respective sides (left and right)
After the stomach has undergone rotation how does it lay?
Horizontally
Where are the cardiac oriface and pyloric oriface oriented?
Cardiac oriface- Left
Pyloric oriface- Right
What does the forgot portion of the duodenum give rise to?
Hepatic diverticulum, bilary system, and pancreatic diverticulum
What causes the duodenum to loose its mesentery
The rotation of the gut causes the duodenum to be pushed against the posterior back wall
Difference between the duodenum in adult verse embryo (other than the fact that the embryo is a straight pole)
The duodenum in the adult is both forgut and hindgut- however, in the embryo that all act as a cohesive unit
What is another name for the hepatic diverticulum
liver bud
Where does the liver bud form from?
Caudal portion of forgut
How are liver cords formed
The liver buds invade the septum transversum
What gives rise to the gallbladder?
The attachment of the hepatic diverticulum to the duodenum then narrows to form the bile duct which in turn gives rise to the glalbladder
How is the ventral mesentery divided into the falciform ligament and the lesser omentum?
Growth of the liver into the septum transversum
How does the hepatic portal vein, hepatic artery, and common bile duct reach the liver?
Through caudal margin of lesser omentum
What action displaces the stomach to the left
The downward growth of the liver
How many pancreatic diverticula develop and where
2 develop in the duodenal region
What are the names of the 2 pancreatic diverticulum
dorsal and ventral pancreatic buds
What embryonic events cause the dorsal and ventral pancreatic buds to fuse together
Growth of liver and stomach causes the duodenum to get pushed back to the posterior body wall (forming C-shaped loop) causing the buds to come together and fuse on to back wall (thus the pancreas becomes secondarily retroperitoneal)
What parts of the pancreas are derived from the ventral pancreatic bud
The head and uncinate process
What is the uncinate process
A part of pancreas that the superior and inferior mesenteric arteries pierce
What are the ventral and dorsal pancreatic buds attached to
Ventral- Common bile duct
Dorsal- Duodenum
What derives from the dorsal pancreatic bud
the body and tail of pancreas
Annular pancreas
When the ventral pancreatic bud constricts the duodenum by forming a ring around it
Is the spleen a forgot derivative?
No
How does the spleen develop
Forms from cells in the dorsal mesentery
Since the dorsal mesentery pushes the spleen against the posterior wall is it secondarily retroperitoneal?
No, it remains in the dorsal mesentery
How is the spleen suspended by the back wall?
Leinorenal ligament (splenorenal ligament)
How is the spleen attached to the stomach
Gatsrosplenic ligament
What ligaments for the lateral wall of the dorsal mesentery
The leinorenal (splenorenal) ligament and gastrosplenic ligament
Where does the midgut region begin
Just caudal to where the common bile duct enters the duodenum
Where does the midgut initially develop
In the extraembryoic coelomic space in the umbilical cord
Why does the midgut form in the umbilical cord?
Because of the rapid growth of the liver (needs more room)
What is it called when a structure (such as the intestines) leave the body (into say the umbilical cord)
Herniation
Midgut rotation sequence
The midgut rotates 90 degrees counterclockwise about the superior mesenteric a. allowing the cecum to develop at the junction of the large and small intestine (remains attached to yolk sac during this)
When is the connection between the midgut and yolk sac gone?
When the midgut is retracted into the abdomen
If the connection between the midgut and yolk sac is not eradicated properly, what abnormalities occur
Meckel’s Diverticulum, Vitelline fistula, and Vitelline cyst
What is the disorder vitelline fistula?
Persistent connection between the ileum and vitelline
What are Meckel’s Diverticulum and Vitelline cyst?
Presence of vitelline ligaments to umbilicus
When the midgut returns to the abdominal cavity, how many more degrees does it rotate
180 degrees counterclockwise around SMA
What portion of the midgut returns to the abdomen first
small intestine
Where does the small intestine go once it reaches the abdomen
To the left and under the SMA
Where does the cecum go once the small intestine has entered the abdomen
To the left (initially) then to the right to sit in the right iliac fossa
Omphalocoele
Results from the failure of the gut to return to the abdomen
Malformation in midgut rotations
Duodenum could be infront of the transverse colon, v.s behind
Where does the mesentery proper attach
Back wall in a left right fashion
Where does the terminal portion of the hindgut enter
cloaca
What is the cloaca
Common changer for feces and urine in the embryo
What are the 2 divisions of the cloaca
urogenital sinus and anorectal canal (purpose: urine and feces are separated)
What is the structure that divides the cloaca into its 2 divisions
urorectal septum
List the forgut derivatives
Pharynx, lungs, bronchi, trachea, esophagus, stomach, superior and descending duodenum, gallbladder, and pancreas
Arterial supply for all forget organs?
Celiac trunk
List all midgut derivatives
Horizontal and Ascending duodenum, jejunum, ileum, ascending colon, proximal 2/3 transverse colon
Arterial supply to midgut organs
Superior mesenteric a
List all hindgut derivatives
Lateral 1/3 of transverse colon, descending colon, sigmoid colon, rectum, anal canal to pectinate line
Arterial supply to hindgut
inferior mesenteric a
Derivatives of ventral mesentery
lesser omentum and falciform ligament
What are the two ligaments that make up the lesser omentum?
Hepatoduodenal ligament and hepatogastric ligament
Derivatives of the dorsal mesentery
- Greater omentum
- Lienorenal (splenorenal) ligament
- Mesentery of jejunum and ileum
- Transverse and Sigmoid mesocolon
- Mesoduodenum (lost in adult)
What are the 3 different ligaments that make up the greater omentum
Gastrocolic, gastrosplenic, Gastorphrenic ligaments
