Digestive System Embryology Flashcards
In what week of development does gastrulation begin?
The third week of development
What marks the beginning of gastrulation?
The formation of the primitive streak on the surface of the epiblast
How many of the germ layers contribute to the formation of the digestive system?
All three germ layers
In the GI tract what does the ectoderm form?
Neural crest cells from the neuroectoderm become neurons of the enteric nervous system
In the GI tract what does the mesoderm form?
Connective tissues, muscular components, and peritoneal components
In the GI tract what does the endoderm form?
Epithelium of GI tract and parenchyma of glands
When does the gut tube initially form?
The 4th week of development
What are parenchyma?
the specific cells of a gland or organ held together by connective tissue called the stroma
The stroma of the glands of the GI tract is derived from what?
The visceral mesoderm
Describe neurulation?
The trilaminar embryonic disc forms the neural plate that rolls up into a tube to from the brain and spinal cord
The mesoderm layer of which holds the neural tube and gut tube together splits into two layers during the 3rd and 4th week and are called what?
Visceral (splanchnic) and parietal (somatic) layers
What does the visceral (splanchnic) layer of the mesoderm do in the 3rd and 4th week of development?
Rolls ventrally, and is intimately connected to the gut tube
What does the parietal (somatic) layer of the mesoderm do in the 3rd and 4th week of development?
Together with the overlying ectoderm, forms the lateral body wall folds, which move ventrally and meed in the midline to close the ventral body wall
What does the vitelline duct and yolk sac eventually get incorporated into?
The umbilical cord
When does the yolk sac typically degenerate?
Around 2 to 3 months of development
By the 4th week of development closure of the ventral body wall is complete except where?
At the connecting stalk
By the 4th week of development closure of the gut tube is complete except where?
At the vitelline duct (yolk sac)
What are the three regions of the gut tube?
Foregut, midgut, and hindgut
Define the each end of the foregut in the 4th week of development.
Oropharyngeal membrane to the liver outgrowth
When does the oropharyngeal membrane rupture?
The 4th week
What is connected when the oropharyngeal membrane ruptures?
The oral cavity and the primitive gut
Define each end of the midgut in the 4th week of development.
Begins caudal to liver and extends to proximal 2/3 of transverse colon
Define each end of the hindgut in the 4th week of development.
From distal 1/3 of transverse colon to cloacal membrane
When does the cloacal membrane break down?
The 7th week of development
What is mesentary?
A double layer of peritoneum that encloses an organ and connects it to the body wall
What is peritoneum?
Thin serous membrane that lines walls of abdominal cavity
Define intraperitoneal.
Organs which are completely enclosed in mesentary and connected to wall via mesentary
Define retroperitoneal.
Organ that lies against posterior body wall and is covered with peritoneum on an anterior surface only
Define serous membrane.
Membrane that lines body cavities (i.e. peritoneal cavity) and produces thin watery lubricating fluid (serous fluid)
Define dorsal mesentary.
This is mesentary that is formed via visceral mesoderm layers meeting and fusing in midline
At the fifth week of development what is suspended in the dorsal mesentary?
The caudal part of the forgut, the midgut, and major part of the hindgut are suspended from the posterior body wall via the dorsal mesentary
At the fifth week of development where does the dorsal mesentary extend from? (what to what)
The lower end of esophagus to cloacal region of hindgut
What are the divisions of the dorsal mesentary?
Dorsal mesogastrium, mesoduodenum, dorsal mesocolon, mesentary proper
Where is the dorsal mesogastrium located and what is it also called?
Located in dorsal mesentary region of the stomach and is also called the greater omentum
Where is the mesoduodenum located?
Dorsal mesentery region of the duodenum
Where is the dorsal mesocolon located?
Dorsal mesentery in region of the colon
Where is the mesentary proper located?
Dorsal mesentery of jejunal and ileal loops
What is the ventral mesentary derived from?
The septum transversum
The central tendon of the diaphragm and connective tissue in the liver is derived from what primary tissue?
The mesodermal tissue
The ventral mesentery exists only in what 3 regions?
Terminal esophagus, stomach, and upper part of duodenum
Specifically what is the central tendon of the diaphragm derived from?
A portion of the septum transversum, consisting of densely packed mesoderm
The developing liver grows in what?
The mesenchyme of the septum transversum
What does the developing liver divide the ventral mesentary into?
The lesser omentum and the falciform ligament
Where does the lesser omentum extend?
Extends from lower portion of esophagus, stomach, and upper portion of duodenum to liver
Where does the falciform ligament extend from?
Extends from liver to ventral body wall
What is the round ligament of the liver?
This is the free inferior margin of falciform ligament and contains obliterated umbilical v.
What is the hepatoduodenual ligament?
This is the free margin of lesser omentum containing duodenum and liver, and contains portal triad
What is the portal triad?
Bile duct, portal v., and hepatic a.
What is the epiploid foramen of Winslow?
This is an opening that connects omental bursa (lesser sac) with the rest of peritoneal cavity (greater sac)
What major artery supplies the foregut?
Celiac (trunk) aftery
What major artery supplies the midgut?
Superior mesenteric artery
What major artery supplies the hindgut?
Inferior mesenteric artery
At the 4th week of development what does the foregut divide into?
Respiratory primordium (ventral), and esophagus (dorsal)
The upper 2/3 of the esophagus has what kind of muscle and is innervated with what?
Striated muscle and Vagus n.
The lower 1/3 of the esophagus has what kind of muscle and is innervated with what?
Smooth muscle and splanchnic plexus
What is the fusiform dilation of the foregut (4th week)?
The stomach
How does the stomach “move” during its development?
It rotates along longitudinal andanteroposterior axis
The Left Vagus nerve eventually innervates what part of the stomach?
The anterior wall
The Right Vagus nerve eventually innervates what part of the stomach?
The posterior wall
During stomach development how far in degrees does the stomach rotate?
90 degrees
What leads to the development of the greater and lesser curvatures of the stomach?
The original posterior wall grows faster than the original anterior portion
Where is the pylorus of the stomach?
Caudal part, towards the end
Where is the cardia of the stomach?
Cephalic part, towards the beginning
What is the omental bursa?
A space created behind stomach from the dorsal mesogastrium being pulled to the left
What is the lienorenal ligament?
This connects the spleen to the body wall in the region of the left kidney
What is the gastrolinal ligament?
This ligament connects the spleen to the stomach
What is the duodenum formed from?
The terminal part of the foregut and cephalic part of the midgut. So simply the foregut and midgut
The duodenum and head of pancreas eventually end up in what peritoneal position?
They become fixed in a retroperitoneal position
What and where is the duodenal cap?
This is a small portion of the duodenum near the pylorus of stomach and is intraperitoneal
Where does the blood supply of the duodenum come from?
Both the celiac a. and superior mesenteric a.
When and how does the liver begin to form?
At the middle of the third week a liver bud appears.
What does the liver bud consist of and where do they penetrate?
Rapidly proliferating cells that penetrate the septum transversum
What forms the (common) bile duct?
The connection between the liver bud and foregut
A small ventral outgrowth is formed by the bile duct and gives rise to what?
The gallbladder and the cystic duct
The pancreas is formed by what two things?
The dorsal pancreatic bud, and a ventral pancreatic bud
Where is the dorsal bud of the pancreas originally found?
Within the dorsal mesentery
Where is the ventral bud of the pancreas originally located?
Close to the bile duct
The ventral bud of the pancreas eventually becomes what?
The uncinate process and inferior part of the head of the pancreas
What is the duct of Wirsung?
The main pancreatic duct
What is the major duodenal papilla?
This is where the main pancreatic duct and bile duct enter the duodenum
What is the Santorini of the pancreas?
An accessory pancreatic duct
When does insulin start to secret from the pancreas?
Approximately 5th month of development
What are the pancreatic islets (islets of Langerhans)?
They are part of the hormonal component of the pancreas
In an adult where does the midgut extend?
Begins just distal to the entrance of bile duct into duodenum and terminates at junction of proximal 2/3 of transverse colon with distal 1/3
What are the three parts of the cephalic limb of the primary intestinal loop?
Distal part of teh duodenum, jujunum, and part of the ileum
What are the five parts of the caudal limb of the primary intestinal loop?
Lower portion of the ileum, cecum, appendix, ascending colon, proximal 2/3 of transverse colon
What is the physiological umbilical herniation?
This is where the abdominal cavity becomes too small for the growing intestinal loops so they herniate into an extraembryonic cavity in the umbilical cord
What are the three most common vitelline duct abnormalities?
Meckel diverticulum, vitelline cyst, and vitelline fistula
The ascending and descending colons are permanently anchored in what position?
Retroperitoneal position (secondarily retroperitoneal)
The appendix, lower end of the cecum and sigmoid colon retain their free mesenteries so they are in what position?
Intraperitoneal
What is the mesentery proper?
Mesentery if the jejunoileal loops
The hindgut gives rise to what?
Distal 1/3 of transverse colon, sigmoid colon, rectum, and upper part of anal canal
The endoderm of hindgut forms what?
internal lining of bladder and urethra
What artery supplies the hindgut?
Inferior mesenteric artery
What is the cloaca?
An endoderm-lined cavity covered at its ventral boundary by surface ectoderm
What is the urorectal septum?
Wedge of mesoderm that separates the region between the allantois and hindgut
What is the proctodeum
AKA the anal pit and is an ectodermally-lined pit in the terminal portion of the hindgut that invaginates to form the lower 1/3 of the anal canal
What is the pectinate line?
This line divides the part of the anal canal in halves derived from the anal pit and the hindgut
