Digestive System Development Flashcards
What week does body folding occur?
Week 4
What forms the innermost lining of the primitive gut tube?
Endoderm from the dorsal portion of yolk sac which is incorporated into the embryo
epithelial lining and glands of the GI tract
Endoderm
What does the yolk sac endoderm form?
Embryonic midgut- with temporary connection with yolk sac
3 regions of the primitive gut tube
Foregut, midgut and hindgut
What does the oropharyngeal membrane develop into
Mouth
What does the cloacal membrane develop into
Anus
Smooth muscle and connective tissue of the GI tract
Splanchnic (visceral) mesoderm
Organs which are completely enclosed in mesentery and connected to wall via mesentery
Intraperitoneal
Organs that lies against posterior body wall and is covered with peritoneum on anterior surface only
Retroperitoneal
The serous membrane lining the abdominal cavity (parietal) & organs (visceral)
Peritoneum
A double-layer of peritoneum that suspends an organ from can contain CT, fat, blood vessels, lymphatics, nerves)
Mesentery
Formed from somatic mesoderm
Parietal
Formed from splanchnic mesoderm
Visceral
What are the caudal part of the foregut, the midgut, and major part of the hindgut suspended from?
Posterior body wall via the dorsal mesentery
Extends from lower end of esophagus to cloacal region of hindgut
Dorsal Mesentery
Formed via visceral mesoderm layers meeting and fusing in midline
Dorsal Mesentery
The connecting tissue bridge has narrowed and the caudal part of the foregut, the midgut, and a major part of the hindgut are suspended from the posterior abdominal wall via the dorsal mesentery by what week
5
Dorsal mesentery in region of the stomach
Dorsal mesogastrium (greater omentum)
Dorsal mesentery in region of the duodenum
Mesoduodenum
Dorsal mesentery in region of the colon
Dorsal mesocolon
Dorsal mesentery of jejunal and ileal loops
Mesentery proper
What are the division of the dorsal mesentery
- Dorsal mesogastrium (greater omentum)
- Mesoduodenum
- Dorsal mesocolon
- Mesentery proper
Fuse in midline, runs for dorsal end of esophagus to hindgut
Dorsal from visceral mesoderm-
Divides that runs the entire length of the GI tract
Dorsal Mesentery
Holds small intestine to internal body wall
Mesentery proper
Mesodermal tissue that gives rise to central tendon of diaphragm and connective tissue in the liver
Septum transversum
Derived from the septum transversum
Ventral Mesentery
Where does ventral mesentery exist?
terminal esophagus, stomach, and upper part of duodenum
What will the portion of the septum transversum, consiting of densely packed mesoderm form?
Central tendon of diaphragm
What is ventral mesetery associated with?
Foregut
Extends from lower portion of esophagus, stomach, & upper portion of duodenum to liver
Lesser Omentum
Extends from liver to ventral body wall
Falciform ligament
Liver grows in the mesenchyme of the septum transversum, dividing ventral mesentery into
Lesser omentum & falciform ligament
Forms the peritoneal connection between the foregut and the ventral abdominal wall
Ventral mesentery
Mesoderm on the surface of the liver differentiates into visceral peritoneum except where?
Cranial surface
Stomach into liver
Lesser omentum
Holds liver to anterior body wall
Falciform ligament
Free inferior margin of falciform ligament
Round ligament of the liver
Contains obliterated umbilical v
Round ligament of the liver
Free margin of lesser omentum connecting duodenum & liver
Hepatoduodenual ligament
Contains portal triad (bile duct, portal v., & hepatic a.)
Hepatoduodenual ligament
What happens to the umbilical vein?
Obliterated after birth
Neural crest cells form the enteric nervous system (brain of the gut) functions without innervation of the brain
Ectoderm
Derived from ectoderm & ectodermal contribution of GI tract
Enteric Nervous System
What artery does the foregut supply?
Celiac (trunk) Artery
What artery does the midgut supply?
Superior mesenteric artery
What artery does the hindgut supply?
Inferior mesenteric artery
What does each gut region suppy?
One of three major arteries off abdominal aorta
- Pharynx
- Lower respiratory system
- Esophagus
- Stomach
- Proximal ½ of duodenum (includes the pancreatic and bile duct papillae)
- Associated organs (liver, gallbladder, biliary system, pancreas, spleen*)
Foregut derivatives
Not a digestive organ but develops with foregut
Spleen
Develops as the portion of the foregut immediately caudal to the pharynx
Esophagus
Endodermal outgrowth from the esophagus
Respiratory diverticulum
Grows out from the ventral side of the foregut & develops respiratory system
Respiratory diverticulum
What week does the respiratory diverticulum appear
During week 4
At what week does a fusiform dilation of the foregut appear?
Week 4
As the stomach enlarges, its dorsal side expands faster than the other sides and will become the
Greater curvature
The ventral side of the stomach will become the
Lesser Curvature
What side of the developing stomach expands faster?
Dorsal
What turn does the stomach take
90 deg clockwise around its longitudinal axis
After the stomach takes a turn, where is the lesser curvature?
On the right
After the stomach takes a turn, where is the greater curvature?
On the left
Where does the Caudal part (Pylorus) of the stomach move?
Upward and to the right
Where does the Cephalic part (cardia) of the stomach move?
Slightly downward and to the left
What happens right after stomach development?
Formation of the omental bursa
As the stomach rotates, what is carried to the left?
Dorsal mesogastrium
Lesser sac of the peritoneum
Omental Bursa
What forms the omental bursa
Dorsal mesogastrium
A mesodermal proliferation within the dorsal mesogastrium
Spleen primordium
What is the spleen location
Intraperitoneal
- Dorsal mesogastrium lengthens
- Portion between spleen & dorsal midline swings to the left; fuses with peritoneum of posterior abdominal wall
Spleen development
Connected to body wall in the region of the left kidney
Lienorenal ligament
Connected to stomach
Gastrolienal ligament
The layers fuse to form a single (4 layer) sheet that hangs from the greater curvature of the stomach
Greater Omentum
What forms the greater omentum
Dorsal mesogatrium extension inferiorly
As stomach rotates, the duodenum becomes
C-shaped
Rotation, together with rapid growth of head of pancreas, swings duodenum from
Midline to right side of the abdomen
Press against dorsal body wall and become fixed in retroperitoneal position
Duodenum and head of pancreas
What appears in the middle of the third week at the distal end of the foregut?
Liver primordium
Appears as an outgrowth of the endodermal epithelium
Liver bud (hepatic diverticulum)
Consists of rapidly proliferating cells that penetrate the septum transversum
Liver bud
Mesodermal plate between pericardial cavity and stalk of the yolk sac
Septum transversum
Hepatic cells invade the septum transversum, the connection between the liver bud and foregut (duodenum) narrows, forming the
Common bile duct
A small ventral outgrowth from the bile duct
Forms gallbladder and the cystic duct
Common bile duct
Connection between liver and bile duct
Cystic duct
What 2 buds form the pancreas?
a dorsal pancreatic bud & a ventral pancreatic bud
Where do pancreatic buds originate from?
Endodermal lining of the duodenum
Within the dorsal mesentery
Dorsal bud
An outgrowth of the bile duct
Ventral bud
What direction does the ventral bud swing as the duodenum rotates?
Clockwise, aligning and fusing with the dorsal bud
Ventral pancreatic bud and Dorsal pancreatic bud fuse forming
Main pancreatic duct
Lies immediately below and behind the dorsal bud
Ventral bud
Forms uncinate process and inferior part head of the pancreas
Ventral bud
Forms all other parts of the pancreas
Dorsal bud
- Distal ½ of the duodenum (just after the major duodenal papilla)
- Jejunum
- Ileum
- Cecum and appendix
- Ascending colon
- Proximal 2/3 of the transverse colon
Midgut derivatives
Forms a U-shaped loop around the superior mesenteric artery
The vitelline duct is the temporary connection between the mid gut and yolk sac
Midgut
Rapid elongation of gut & its mesentery results in formation of the
Primary intestinal loop
What does the Cephalic limb become?
Distal part of duodenum, Jejunum, & proximal ileum
What does the Caudal limb become?
Distal ileum, Cecum, Appendix, Ascending colon, Proximal 2/3 of transverse colon
Why does the abdominal cavity temporarily become too small to contain all the intestinal loops?
Rapid growth and expansion of the liver
Loops enter the extraembryonic cavity in the umbilical cord
Physiological Umbilical Herniation
When does Physiological Umbilical Herniation occur?
6th-10th week
When is the first midgut rotation?
Week 6
What happens in the 1st midgut rotation?
90 deg counterclockwise rotation around the superior mesenteric artery
Initial growth and coiling of the small intestine
1st midgut rotation
What happens in the 2nd midgut rotation?
As the intestines return into the abdominal cavity, a 180° counterclockwise rotation brings them back to their normal position
When does the second midgut rotation occur?
Week 10
What brings the cecum down?
Cecal swelling
Where are the ascending & descending colons permanently anchored?
Retroperitoneal position
What happens when ascending and descending colons obtain their final positions?
Their mesenteries press against peritoneum of posterior abdominal wall
Fuses with posterior wall of greater omentum, but maintains its mobility
Transverse mesocolon
Mesentery of the jejunoileal loops
Mesentery proper
Line of attachment extends from area where duodenum becomes intraperioneal, to the ileocecal junction
Mesentery proper
Meseteries are named for..
What they surround
Line of attachment extends from the hepatic flexure of ascending colon to splenic flexure of descending colon
Transverse mesocolon
Total rotation
270 deg Counterclockwise
90° CCW rotation while loop is in proximal umbilical cord
1st rotation
180° CCW rotation as intestines return to abdomen
2nd rotation
Proliferation of endodermal lining completely occludes the gut tube during what week of development
during the 6th week
When is the gut tube recanalized completely?
By 9th week of development
A remnant of the vitelline (omphaloenteric) duct persists as a finger-like outpouching of the ileum ~40-60 cm from ileocecal junction
Meckel’s (Ileal) diverticulum
May contain pancreatic tissue/gastric mucosa that secretes acid, causing ulcers & bleeding
Diverticulum
The most common GI malformation, occurring in 2% of population with a male predominance
Meckel’s (Ileal) Diverticulum
When vitelline duct doesn’t close properly
Meckel’s (Ileal) Diverticulum
GI tract completely open to outside world
Fistula
Tissue remains in what was vitalline duct
Cyst
- Distal 1/3 of the transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Superior portion of the anal canal
Hindgut Derivatives
Grows inferiorly toward the cloacal membrane, dividing it into urogenital and anal membranes
Urorectal septum
What does the urorectal setpum divide the cloaca into?
Urogenital sinus (ventrally) & anorectal canal (dorsally)
When does the cloacal membrane ruptures, creating anal opening for the hindgut & ventral opening for the urogenital sinus?
End of 7th week
Gives rise to urinary and anal canal
Urogenital sinus
Mesodermal proliferation
Ureoctal septum
Superior 2/3 of anal canal derived from
Endoderm of hindgut
Inferior 1/3 of anal canal derived from
Invaginating ectoderm around proctodeum
Proliferates & invaginates to create anal pit
Ectoderm in region of the anus
Known as anal pit
Proctodeum
An ectodermally-lined pit in the terminal portion of hindgut that invaginates to form the lower 1/3 of the anal canal
Proctodeum
Establishes continuity between upper & lower parts of anal canal
Anal membrane
Junction between endodermal & ectodermal regions of anal canal is delineated by
Pectinate line
What does epithelial in the anal membrane change
Columnar to stratified squamous epithelium
