Lecture 1 - Development of the Digestive System Flashcards
Foregut and hindgut form during which type of folding of the embryo
cranial and caudal folding
Endoderm from the dorsal yolk sac is incorporated into the embryo forming the
epithelial lining and the glands that are going to make up the inner most lining of our GI tract
the cranial fold with the oropharyngeal membrane as the hinge joint is incorporated as the embryologic ____
foregut
the caudal fold with the cloacal membrane as the hinge joint is incorporated as the emryologic __
hindgut
epithelial lining and glands of the GI tract
endoderm
During body folding (Week 4), endoderm from the ____ portion of yolk sac is incorporated into the embryo, forming the innermost lining of the primitive gut tube (the epithelial lining and glands of the G.I. tract).
dorsal
During lateral folding, yolk sac endoderm is incorporated as embryonic ___
midgut
forms the smooth muscle and connective tissue of the GI tract
Splanchnic (visceral) mesoderm
when we hear “peritoneum” think
abdomen
the serous membrane lining the abdominal cavity (parietal) & organs (visceral)
peritoneum
a double-layer of peritoneum that suspends an organ from the body wall
(can contain CT, fat, blood vessels, lymphatics, nerves)
mesentery
organs which are completely enclosed in mesentery and connected to wall via mesentery
Intraperitoneal
organ that lies against posterior body wall and is covered with peritoneum on anterior surface only
Retroperitoneal
somatic mesoderm or
parietal (body)
splanchnic mesoderm
visceral or dorsal (organ)
what is holding the midgut to the posterior body wall
dorsal mesentery
Formed via visceral mesoderm layers meeting and fusing in midline
dorsal mesentery
The caudal part of the foregut, the midgut, and major part of the hindgut are suspended from the posterior body wall via the
dorsal mesentery
Extends from lower end of esophagus to cloacal region of hindgut
dorsal mesentery
Divisions of dorsal mesentery:
(4)
Dorsal mesogastrium (greater omentum)
Mesoduodenum
Dorsal mesocolon
Mesentery proper
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
Derived from the septum transversum:
ventral mesentery
Mesodermal tissue that gives rise to central tendon of diaphragm and connective tissue in the liver
ventral mesentery
associate ventral mesentery with
foregut
Exists only in region of terminal esophagus, stomach, and upper part of duodenum
ventral mesentery
Liver grows in the mesenchyme of the septum transversum, dividing ventral mesentery into:
______– extends from lower portion of esophagus, stomach, & upper portion of duodenum to liver
____– extends from liver to ventral body wall
Lesser omentum – extends from lower portion of esophagus, stomach, & upper portion of duodenum to liver
Falciform ligament – extends from liver to ventral body wall
Free inferior margin of falciform ligament
Contains obliterated umbilical v.
Round ligament of the liver (Ligamentum teres hepatis)
Free margin of lesser omentum connecting duodenum & liver
Contains portal triad (bile duct, portal v., & hepatic a.)
Hepatoduodenual ligament
bile duct, portal v., & hepatic a. make up what
portal triad
enteric nervous system (no connecting to the brain, operates alone) is derived from
neuroectoderm neural crest cells
run from the pharynx and esophagus all the way down to the proximal half the the duodenum
foregut
run from the the distal half of the dueodenum all the way to the proximal 2/3 of the transverse colon
midgut
run from the distal 1/3 of the transverse colon all the way down out through the anus
hindgut
3 unpaired branches off the abdominal artery
celiac (trunk) artery
Superior mesenteric artery
inferior mesenteric artery
the 3 unpaired branches of the abdominal artery and what they supply
foregut?
midgut?
hindgut?
foregot - celiac trunk a.
midgut - superior mesenteric a.
hindgut - inferior mesenteric a.
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
foregut derivative that includes the pancreatic and bile duct papillae)
proximal 1/2 of the duodenum
Not a digestive organ but develops with foregut in mesoderm
spleen
develops as the portion of the foregut immediately caudal to the pharynx
esophagus
from the esophagus we get an endodermal outgrowth
respiratory diverticulum (or tracheobronchial diverticulum or lung bud)
During week 4, ____ appears on ventral side of foregut (will become the trachea, respiratory tree & lungs)
a respiratory diverticulum
Week 4: Appears as a fusiform dilation of the foregut.
stomach
As the stomach enlarges, its ___ side expands faster than the other sides and will become the greater curvature. The ____side of the stomach will become the lesser curvature.
dorsal side - greater curve
Ventral side - lesser curve
first rotation of the development of the digestive system
occurs at the stomach
Stomach undergoes 90° clockwise rotation around its
longitudinal axis
during stomach rotation, Ventral side (lesser curvature) ends up on the __, dorsal side (greater curvature) ends up on the ___
ventral lesser curve ends up on the right
dorsal greater curve ends up on the left
As stomach rotates, the dorsal mesogastrium (dorsal mesentery of stomach) is carried to the left. This enlarges a space posterior to the stomach -
the omental bursa (lesser sac of peritoneum)
a mesodermal proliferation within the dorsal mesogastrium
spleen primordium
as the stomach rotates so does the spleen, Portion between spleen & dorsal midline swings to the left; fuses with peritoneum of posterior abdominal wall
Spleen remains ____
intraperitoneal
2 ligaments of the spleen:
______– connected to body wall in the region of the left kidney
_____ – connected to stomach
Lienorenal ligament – connected to body wall in the region of the left kidney
Gastrolienal ligament – connected to stomach
As a result of stomach rotation, dorsal mesogastrium extends inferiorly
Forms a double-layered sac that extends over the transverse colon & small intestine loops
The layers fuse to form a single (4 layer) sheet that hangs from the greater curvature of the stomach ____
the greater omentum
first portion of the small intestine
duodenum
As stomach rotates, the ____ becomes a C-shaped
Rotation, together with rapid growth of head of pancreas, swings ___(same) from midline to right side of abdomen
duodenum
Duodenum and head of pancreas press against dorsal body wall, become fixed in
retroperitoneal position
Dorsal mesoduodenum disappears completely except in region of ___, where small portion of duodenum retains its mesentery and is intraperitoneal
pylorus of stomach
In the middle of the 3rd week, ____ appears at the distal end of the foregut as an outgrowth of the endodermal epithelium
liver primordium
This outgrowth, known as ____, consists of rapidly proliferating cells that penetrate the septum transversum
the liver bud (hepatic diverticulum)
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
connection between the gallbladder and the bile duct is the
cystic duct
The pancreas is formed by 2 buds:
These buds originate from the endodermal lining of the duodenum
a dorsal pancreatic bud & a ventral pancreatic bud
Pancreas buds: The____ bud is within the dorsal mesentery; the __bud is an outgrowth of the bile duct
dorsal
ventral
Pancreas: As the duodenum rotates, the ventral bud swings with it in the clockwise direction until aligning and fusing with the ___
Fusion of the Main and Accessory Pancreatic Ducts
dorsal bud
Pancreas: Ventral bud comes to lie immediately below and behind the dorsal bud
___ bud: forms uncinate process and inferior part head of the pancreas
_____bud: forms all other parts of the pancreas
Ventral bud: forms uncinate process and inferior part head of the pancreas
Dorsal bud: forms all other parts of the pancreas
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
axis of all midgut rotations
superior mesenteric a.
Midgut forms a U-shaped loop around the superior mesenteric artery
The ____ is the temporary connection between the mid gut and yolk sac
vitelline duct
midgut: Rapid elongation of gut & its mesentery results in formation of the
primary intestinal loop
midgut: primary intestinal loop \_\_\_\_\_limb becomes: Distal part of duodenum Jejunum Proximal ileum \_\_\_\_limb becomes: Distal ileum Cecum Appendix Ascending colon Proximal 2/3 of transverse colon
Cephalic limb becomes:
Distal part of duodenum
Jejunum
Proximal ileum
Caudal limb becomes: Distal ileum Cecum Appendix Ascending colon Proximal 2/3 of transverse colon
Midgut: Due to rapid growth & expansion of liver, ___temporarily becomes too small to contain all the intestinal loops
abdominal cavity
In the 6th–10th weeks, these midgut loops enter the extraembryonic cavity in the umbilical cord forming __ to account for not enough space for development
Physiological Umbilical Herniation
1st midgut rotation: while things are being pushed out via the umbilical herniation, 90° Counterclockwise rotation (when viewed anteriorly) around the superior mesenteric artery
Initial growth and coiling of
the small intestine
2nd midgut rotation: As the intestines return into the abdominal cavity, ____ rotation brings them to their final position during week 10
a 180° counterclockwise
When ascending & descending colons obtain their final positions, their mesenteries press against peritoneum of
posterior abdominal wall
the ascending & descending colons are permanently anchored in a
retroperitoneal position (secondarily retroperitoneal)
The appendix, lower end of cecum, and sigmoid colon, however, retain their free mesenteries and are located
intraperitoneal
fuses with posterior wall of greater omentum, but maintains its mobility (intraperitoneal)
Transverse mesocolon
mesentery of the jejunoileal loops
Line of attachment extends from area where duodenum becomes intraperioneal, to the ileocecal junction
Mesentery proper
___ line of attachment extends from the hepatic flexure of ascending colon to splenic flexure of descending colon
Transverse mesocolon’s line of attachment extends from the hepatic flexure of ascending colon to splenic flexure of descending colon
midgut rotation summary
Total Rotation: 270° Counterclockwise
1st rotation: 90° CCW rotation while loop is in proximal umbilical cord
2nd rotation: 180° CCW rotation as intestines return to abdomen
Direction of rotation is assuming an anterior view
SMA is the axis of rotation
Proliferation of endodermal lining completely occludes the gut tube during 6th week of development
Gut tube ____ is completed by 9th week of development
recanalization
clinical correlation : A remnant of the vitelline (omphaloenteric) duct persists as a finger-like outpouching of the ileum ~40-60 cm from ileocecal junction
Diverticulum may contain pancreatic tissue/gastric mucosa that secretes acid, causing ulcers & bleeding
The most common GI malformation, occurring in 2% of population with a male predominance
Meckel’s (Ileal) Diverticulum
Distal 1/3 of the transverse colon Descending colon Sigmoid colon Rectum Superior portion of the anal canal
hindgut derivatives
Hindgut: A ____ grows inferiorly toward the cloacal membrane, dividing it into urogenital and anal membranes and partitioning the cloaca into the urogenital sinus (ventrally) and the anorectal canal (dorsally).
urorectal septum
End of 7th week, ___membrane ruptures, creating anal opening for the hindgut & ventral opening for the urogenital sinus
cloacal
Superior 2/3 of anal canal derived from ____ of hindgut
endoderm
Inferior 1/3 of anal canal derived from invaginating ____around proctodeum
ectoderm
Ectoderm in region of the anus proliferates & invaginates to create
anal pit
The____degenerates
Establishes continuity between upper & lower parts of anal canal
anal membrane
Junction between endodermal & ectodermal regions of anal canal is delineated by _____,
pectinate line
in the anal canal, between the pectinate line and white line what is happening with epithelium
Epithelium changes from columnar to stratified squamous epithelium
