Endoderm Development

The epiblast and hypoblast (primitive endoderm) together form the

Bilaminar germ disc

The hypoblast cells that contact the epiblast are called the

________ contacts the cytotrophoblast

visceral endoderm

parietal endoderm

Gastrulation

The first epiblast cells that move through the primitive streak will displace the hypoblast (visceral endoderm) and from the definitive endoderm, or endoderm found in the embryo

Endoderm During Gastrulation

• During gastrulation the definitive endoderm intercalates with the visceral endoderm.

• Some visceral endoderm is trapped in the definitive endoderm and persists in the embryo, while most of the visceral endoderm is displaced to extraembryonic regions.

• The first cells moving through the primitive streak form

mesoderm

• High levels of Nodal signaling promote expression

of Sox17, a pioneer transcription factor for endoderm.

BMP and FGF promote

• Brachyury expression and a mesodermal fate.

As with ectoderm and mesoderm

BMP, FGF, and WNT promote development of posterior endoderm.

Lower levels of these factors leads to anterior endoderm

Three different regions of endoderm are generated based on paracrine factor concentration.

• Anterior foregut

• Posterior foregut

• Midgut-hindgut

• Each region of endoderm will generate different regions of the digestive tube and progenitors for specific organs.

• Anterior foregut produces __________

• Posterior foregut produces ________

• Midgut hindgut produces ________

• lung and thyroid progenitors

• liver and pancreas progenitors

• intestinal progenitors.

• WNT signaling is _________

• High CDX expression promotes_______

• Lower CDX expression promotes ________

• WNT signaling is inhibited in

• high posteriorly and induces expression of CDX1 and CDX2 in the endoderm 

• large intestine formation

• small intestine formation

• SOX2 expression and stomach and esophagus formation.

Body Folding

• The developing endoderm is initially open to the yolk sac

• Longitudinal folding at both ends of the embryo and lateral folding at the sides of the embryo bring the endoderm inside and form the gut tube.

The yolk sac is incorporated into the __________

The allantois is a blind tube projecting from the ________

• The bladder will form from the _______

• The allantois becomes ______

umbilicus and is connected to the gut tube via the vitelline duct

• hindgut that stores urine from the mesonephros and metanephros

  • hindgut endoderm connected to the allantois

  • incorporated into the umbilicus.

• A failure to close the body wall can result in _____

• omphalocele, where membrane covered bowel herniated through the umbilical ring

• The _______ _______ is a thick wedge of mesoderm adjacent to the heart tube that will separate the thoracic and abdominal cavities

septum transversum

• There are two locations where ectoderm and endoderm meet, the

• oropharyngeal membrane and the cloacal membrane.

• These locations are initially sealed, but break open to form the opening of the esophagus and the anus

Dorsal Mesentery

Splanchnic mesoderm surrounds the gut tube

• The______ is the thin bilayered ,mesoderm that suspends the gut tube in the intraembryonic coelom, which will become the _________

• dorsal mesentery

• peritoneal cavity

• Organs inside the peritoneal cavity are _______

• intraperitoneal viscera

• Organs, like the kidneys and bladder, that are outside of the peritoneal cavity and within the body wall are ______

• retroperitoneal

• Organs, like the ascending and descending colon and pancreas become fused to the body wall but are still inside the peritoneum are said to be

• secondarily retroperitoneal.

• The endoderm will generate the

• digestive tube, and associated organs, including liver, gallbladder, and pancreas

• The respiratory tube forms as an endoderm outgrowth the

• The ________ is a blind tube leading from a cavity.

• respiratory diverticulum, which will bifurcate and form the lungs.

• diverticulum

• The region of the gut anterior to the respiratory diverticulum is the

• pharynx.

• Foregut -

• Midgut -

• Hindgut -

• celiac artery

• superior mesenteric artery

• inferior mesenteric artery.

• The oral epithelium in the mouth and nasal cavity is derived from

• surface ectoderm, along with the teeth and Rathke's pouch ( the precursor to the pituitary anterior lobe)

• The posterior epithelium of the tongue (blue stain), some taste bud epithelium, and esophagus are

• endoderm derived.

• The internal lining of the pharyngeal region is

• endoderm

• In between each pharyngeal arch is an

• Specific structures and organs are derived from the

• endodermal pharyngeal pouch.
  pharyngeal pouches

• Pouch 1 -

• Pouch 2 -

• Pouch 3 -

• Pouch 4 -

• auditory tube

• tonsils

• parathyroid and thymus

• parathyroid and post branchial body, which contributes to thyroid.

• Derivatives of pharyngeal pouches 3 and 4 migration to locations in the

• neck and thorax

• The thyroid gland develops from a

• The thyroid migrates posteriorly and integrates the

• thickening on the ventral floor of the pharynx (foremen cecum)

• post branchial body from the 4th pouch.

The Digestive Tube

combination of endoderm and splanchnic mesoderm

only the epithelial lining of the digestive tube is endoderm derived

The splanchnic mesoderm develops into the

connective tissue and smooth muscle that generates the peristaltic movements of the gut.

• The thoracic foregut, which is caudal to the septum transversum, expands to from the ______

• The dorsal wall proliferative faster than the ventral wall, generating the _____

• stomach

• greater curvature of the stomach

• The stomach rotates 90 degrees.

Foregut Acessory Organs

The liver, gallbladder, and pancreas are derived from endodermal buds and associated splanchnic mesoderm.

Liver Development

The cardiogenic mesoderm and septum transversum are on the ventral side of the endoderm.

• Heart mesoderm secretes ____ and the septum transversum secretes ___

• A hepatic diverticulum forms that grows towards the septum transversum

• The hepatic diverticulum will branch and differentiate into hepatocytes, the precursor cells for the liver parenchyma.

• When the stomach rotates, the liver also rotates, moving from the midline to the right side.

• FGFs

• BMPs that promotes liver formation

• A _______ forms that grows towards the septum transversum

• The hepatic diverticulum will branch and differentiate into ____

• hepatic diverticulum

• hepatocytes, the precursor cells for the liver parenchyma.

• When the stomach rotates, the liver also

• rotates, moving from the midline to the right side.

Gallbladder Development

A cystic diverticulum will bud from the base of the hepatic duct and form the gallbladder.

Pancreas Development

• SHH is expressed throughout the digestive tube

• In the region where the pancreas buds, FGF2 and activin signals from the notochord inhibit SHH expression, making the region competent to form pancreas

• In the competent region, contact with major blood vessels induces expression of

• The dorsal pancreatic bud forms the _____

• The ventral pancreatic bud forms the ____

• PDX1, a key transcription factor for pancreas development.

• dorsal pancreas

• ventral pancreas. Which migrates to the dorsal side and fuses with the dorsal pancreas.

• Two ventral pancreatic buds can form that

• Two buds will encircle the intestine and form an _____ ______

• migrate in opposite direction to join the dorsal pancreas

• annular pancreas and cause an obstruction, or duodenal stenosis.

• B-cells in the pancreas secrete

• Type 1 diabetes result from a

• insulin, which regulates blood glucose levels

• loss of B-cells

Midgut Development

• Growth of GI tract exceeds volume of abdominal cavity, so the midgut region herniates into the umbilicus and forms a primary intestinal loo

• While herniated the primary intestinal loop rotates 90 degrees positioning the

• The abdominal cavity expands with growth of the fetus, drawing the gut tube back inn while rotating an additional 180 degrees, positioning the

• Growth of the colon pushes the

• appendix on the left.

• appendix on the right

• appendix to its final position in the lower right quadrant.

Meckel’s Diverticulum

• Occurs when the vitelline ducts fails to completely regress

• Mostly asymptomatic

• In the mature small intestine, epithelial cells are constantly lost form the tips of the villi through an apoptotic mechanism, called _____

• anoikis

• Lost cells need to be replaced.

• _____ are deep recesses in the intestinal epithelium

• Crypts

• The base of the crypt houses a stem cell population.

• Stromal cells adjacent to the crypt secrete WNT2B, which promotes proliferation

• ____ signaling from cells further up the crypt promote differentiation

• WNT2B, which promotes proliferation

• BMP

______ in the intestine shows the progression of stem cell descendants from the crypt to the top of the villus.

LacZ lineage tracing

Loss of ____ shifts balance of cell types in the intestine, such that more goblet cells are made.

Itch

Hindgut Development

• The large intestine is derived from the hindgut

• Does not have the villi found in the small intestine.

Hirschsprung's Disease

• Insufficient innervation of the colon by the enteric nervous system

• Results in aganglionic (no neurons) segment and a constriction.

Defects in neural crest migration and proliferation.

• The _____ is an expansion of the hindgut, cranial to the cloacal membrane

• The urorectal septum divides the cloaca into

• cloaca

• a urogenital sinus and an anorectal canal.

• The urogenital sinus forms the bladder

• An _____, forms at the border of the anal opening

• The boundary between ectoderm from the anal pit and endoderm from the hindgut occurs at the

• anal pit, or proctodeum

• pectinate line

• The lungs develop from

• pharyngeal endoderm in combination with splanchnic mesoderm

• A _________ forms in the ventral floor of the pharynx between the 4th pharyngeal pouches.

• laryngotracheal groove, or respiratory diverticulum,

• The groove bifurcates to form the paired bronchi and lung buds

• Separation of the respiratory diverticulum from the pharynx forms

• the trachea and esophagus.

• The mesenchyme adjacent to the endoderm induces its fate.

• _____ signaling on the ventral side promotes ______ and _______

• Dorsal mesenchyme secretes

• WNT, tracheal development and formation of the ciliated epithelium

• sFRP, which inhibit WNT, promoting esophageal formation

• Failure to separate the trachea from the esophagus results in a

• tracheal-esophageal fistula.

• If tracheal mesenchyme, instead of lung mesenchyme is placed next to developing bronchus,

• Branching in the lung is not random, but follows a

• branching is inhibited.

• stereotypical pattern

• _____ signaling in the lung mesenchyme promotes epithelial growth

• _____signaling in the epithelium inhibits proliferation

• ____ from the epithelium inhibits _____

• _____ is then expressed laterally, leading to two new branches

FGF10

• BMP4

• SHH, FGF10

• FGF10

• The primitive heart tube is surrounded by a _____

• ______ grow out from the body wall towards the midline to separate the pericardial cavity from the pleural cavity. 

• pericardial cavity

• Plueropericardial folds

• The septum transversum divides the primitive pericardial cavity from the peritoneal cavity, leaving

• _____ grow ventrally from the dorsal body wall to meet the septum transversum and close the pericardioperitoneal canals, separating the peritoneal cavity from the pleural cavity.

• pericardioperitoneal canals dorsally.

• Pleuroperitoneal folds

• The pleuroperitoneal folds form the

• Myoblasts migrate across the connective tissue to form the ______

• connective tissue of the diaphragm

• musculature.

Congenital Diaphragmatic Hernia

• Failure to form the diaphragm completely allows the abdominal viscera to bulge into the pleural cavity

• Can inhibit lung growth.