Endoderm Development

the epiblast and hypoblast together form the

bilaminar germ disc

the hypoblast cells that contact the epiblast are called

visceral endoderm

parietal endoderm contacts the

cytotrophoblast

the first epiblast cells that move through the primitive streak will dispace the hypoblast (visceral endoderm) and form the

definitive endoderm (found in embryo)

during gastrulation, the definitive endoderm intercalates with the

visceral endoderm

some visceral endoderm persists in the embryo while most is

displaced into extraembryonic regions

the first cells moving through primitive streak form

mesendoderm

high levels of Nodal signaling promote

Sox17 expression which is a pioneer transcription factor for endoderm

BMP and FGF promote

Brachyury expression and a mesodermal fate

BMP, FGF and WNT promote

development of posterior endoderm

anterior foregut produces

lung and thyroid progenitors

posterior foregut produces

liver and pancreas progenitors

midgut hindgut produces

intestinal progenitors

WNT signaling is high

posteriorly

WNT signaling induces expression of

CDX1 and CDX2 in the endoderm

high CDX expression promotes

large intestine formation

lower CDX expression promotes

small intestine formation

WNT signaling is inhibited by anterior regions, resulting in

SOX2 expression and stomach and esophagus formation

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 umbilicus and is connected to the gut tube via the

vitelline duct

a blind tube projecting from the hindgut that stores urine from the mesonephros and the metanephros

allantois

the bladder will form from

the hindgut endoderm connected to the allantois

the allantois becomes

incorporated into the umbilicus

omphalocele

a failure to close the body wall can result in this, where membrane covered bowel herniates through the umbilical ring (1 in 5k births)

septum transversum

thick wedge of mesoderm adjacent to the heart tube that will separate the thoracic and abdominal cavities

2 locations where ectoderm and endoderm meet

oropharyngeal membrane and the cloacal membrane

oropharyngral membrane becomes

esophagus

cloacal membrane becomes

the anus opening

what kind of mesoderm surrounds the gut tube

splanchnic

dorsal mesentary

thin, bilayered mesoderm that suspends the gut tube in the intraembryonic coelomth

the intraembryonic coelom becomes

peritoneal cavity

intraperitoneal

organs inside the peritoneal cavity

retroperitoneal

organs like the kidneys/bladder outside of peritoneal cavity but within the body wall

secondarily retroperitoneal

organs like ascending and descending colon and pancreas, that become fused to body wall but are still inside the peritoneum

the endoderm will generate the

digestive tube and associated organs (liver, gallbladder and pancreas)

the respiratory tube forms as an

endoderm outgrowth, the respiratory diverticulum

the respiratory diverticulum bifurcates and forms

lungs

pharynx location

region of the gut anterior to the respiratory diverticulum

foregut artery

celiac

midgut artery

superior mesenteric artery

hindgut 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 (precursor the the pituitary anterior lobe)

the posterior epithelium of the tongue and some taste bud epithelium and esophagus are derived from

endoderm

the internal lining of the pharyngeal region is

endoderm

inbetween each pharyngeal arch is an

endodermal pharyngeal pouch

pouch 1

auditory tube

pouch 2

tonsils

pouch 3

parathyroid and thymus

pouch 4

parathyroid and postbranchial body, contributes to thyroid

thyroid gland development

develops from a thickening on the ventral floor of the pharynx (foramen cecum)

the thyroid gland migrates

posteriorly and integrates the postbranchial body from the 4th pouch

only the epithelia 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 expands to

form the stomach

the dorsal wall proliferates faster than the ventral wall generating the

greater curvature

the stomach rotates

90 degrees

heart mesoderm secretes _ and the septum transversum secreates _ to promote liver formation

FGFs; BMPs

hepatic diverticulum

is an outgrowth of the foregut endoderm that develops into the liver and biliary system during embryonic development

the hepatic diverticulum branches and differentiates inot

hepatocytes

hepatocytes

the precursor cells for the liver parenchyma

gallbladder development

a cystic diverticulum will bud from the base of the hepatic duct to form it

FGF2 and activin signals from the notochord inhibit (in pancreas buds)

SHH expression

low SHH expression (in pancreas buds)

promote pancreatic development

PDX1 is a key transcription factor for

pancreas development

mutations in Indian Hedgehog are associated with

annular pancreas and duodenal stenosis

B-cells secrete

insulin to regulate blood glucose

loss of B-cells results in

Type 1 diabetes

one potential T1D therapy

cell replacement therapy of B-cells derived from iPS cells

midgut development

GI tract growth exceeds abdominal cavity so midgut herniates into umbilicus to form primary intestinal loop, the loop rotates 90 deg to position appendix on the left, the cavity then expands with the fetus drawing gut tube back in and rotating it addition 180 deg to position appendix on the right, the colon growth causes appendix to push to the right lower quadrant of the abdomen

Meckel’s diverticulum

congenital anomaly that occurs when the vitelline duct fails to completely regress (2% of population), mostly asymptomatic

the mature small intestine loses epithelial cells through

anoikis

crypts are deep recesses in the intestinal epithelium that

house a stem cell population to replace cells lost during anoikis

stromal cells adjacent to the crypt secrete

WNT2B to promote proliferation

BMP from cells further up the crypt promote

differentiation

stem cell descendants leaving the crypt become

transit amplifying cells before differntiating into mature intestinal cells

LacZ lineage tracing in the intestine shows

progression of stem cell descendants from the crypt to the top of the villus

the large intestine is derived from

hindgut

does the large intestine have villi found in the small intestine

no

Hirschsprung’s Disease

insufficient innervation of the colon by the enteric nervous system that results in an aganglionic (no neurons) segment and constriction, occurs 1 in 5000, defects in neural crest migration and proliferation

the cloaca is an expansion of the

hindgut

the urorectal septum divides the cloaca into

urogenital sinus and an anorectal canal

the urogenital sinus forms the

bladder

an anal pit or proctodeum forms at the

border of the anal opening

the pectinate line

the boundary between ectoderm from anal pit and endoderm from hindgut

the lungs develop from

pharyngeal endoderm in combo with splanchnic mesoderm

laryngotracheal groove or respiratory diverticulum forms

in the ventral floor of the pharynx between the 4th pharyngeal pouches

the laryngotracheal groove bifurcates to form

the paired bronchi and lung buds

separation of the respiratory diverticulum form the pharynx forms the

trachea and esophagus

WNT signaling on ventral side promotes (lung development)

tracheal development and formation of a ciliated epithelium

dorsal mesenchyme secretes sFRP which

inhibits WNT to promote esophageal formation

tracheal-esophageal fistula

failure to separate the trachea from the esophagus (1 in 3k births)

branching in the lung is __ random

NOT

the mesenchyme adjacent to the paired bronchi causes

branching

FGF10 signaling in the lung mesenchyme promotes

epithelial growth

BMP4 signaling in the epithelium inhibits

proliferation

SHH from the epithelium inhibits

FGF10

FGF10 is expressed laterally leading to

2 new branches

constriction of smooth muscle promotes

branch formation

combo of FGF10 signaling and smooth muscle contraction results in

mammalian branching behavior

the primitive heart tube is surrounded by

pericardial cavity