Lecture 4 - Embryo (Reep!) Flashcards
after regional specification, the gut endoderm interacts with what two things to form specific structures?
surrounding mesenchyme and splanchnic mesoderm
when does regionalizationof endodermal gene expression occur?
early - prior to gut tube formation
what does transverse folding of tilaminar embryo form?
gut tube
head fold and tail fold create what?
foregut and hindgut
lateral body folds create what?
closure at midline
what are the major components of gut development
endoderm, splanchnic mesoderm and neural crest
how does the trachea begin?
as an outgrowth of the esophagus
when does the esophagus elongate?
during growth of cervical and thoracic regions
what are the 3 mechanisms of development of the stomach and describe each one briefly
displacement: caudally, due to elongation of esophagus
reorientation: rotation of stomach; creates greater and lesser omenta
differential enlargement: formation of fundus
describe the develoment of the compound stomach
initially develops like a simple glandular stomach
by the end of the first month:
rumen and reticulum develop from the fundic region
omasum and abomasum develop from the lesser curvature
describe the development of the liver
the hepatic diverticulum is an outgrowth of the foregut into the mesenchyme os the septum transversum
where do hepatocytes derive from?
endoderm of foregut
where does the gall bladder originate from
buds off hepatic diverticulum
which animals do not have a gall bladder?
horse and rat
what induces the hepatic diverticulum to begin branching? what does the branching form?
under the inductive influence of the surrounding mesenchyme.
the branching forms hepatic buds that differentiate into hepatocytes and biliary cells that form the biliary duct system
endoderm is induced to become hepatic buds by what 3 structures and associated signals
- cardiac mesoderm via FGF
- septum transversum mesoderm via BMP
- endothelial cells via an unknown signal
how do the hepatic buds develop into hepatoblasts?
the hepatic buds interact with surrounding mesenchyme and proliferate as hepatoblasts
what does Notch signaling do?
it transforms some hepatoblasts into biliary epithelial cells.
without the presence of Notch signaling, they develop into hepatocytes
what do hepatoblasts differentiate into with the presence of Notch signaling?
absence of Notch signaling?
presence of Notch: hepatoblasts differentiate into biliary epithelial cells
absence of Notch: hepatoblasts become hepatocytes
describe the development of the intra and extra hepatic portions of the biliary system?
they develop independently initially and eventually anastomose
what two things seen together imply a common genetic dysfunction?
- biliary cysts
2. polycystic kidneys
what does the dorsal pancreatic diverticulum arise from? what does it form?
arises from duodenum to form left lobe and accessory pancreatic duct
what does the ventral pancreatic diverticulum arise from? what does it form?
arises from hepatic diverticlum and forms the right lobe and pancreatic duct
describe the development of the small intestine
- loss of yolk sac
- evagination of cecum
- rapid elongation of small intestine into umbilical stalk
- rotation of intestinal loop about cranial mesenteric artery
- withdrawal of small and large intestines from umbilical stalk
describe the shape of the large intestine, ascending colon for the dog, horse, cattle, and pig
dog: straight
horse: sharply bent (volvulus can occur at bend)
cattle: flatly coiled
pig: spiral
what can occur at the bend of the horse’s large intestine, ascending colon?
volvulus - a twisting of the intestine; constriction and atrophy
what separates the cloaca into the rectum and urogenital sinus?
the urorectal septum
define stenosis
local narrowing of gut lumen
define atresia
closure of gut lumen; becomes critical at birth
what are the 4 most common examples of stenosis and atresia?
atresia ani (imperforate anus)
rectal atresia
esophageal stenosis or atresia - often accompanied by tracheoesophageal fistula
intestinal stenosis or atresia
where is atresia most commonly seen in the cow?
jejunum, colon, rectum
where is atresia most commonly seen in the pig?
rectum
where is atresia most commonly seen in the cat?
colon
where is atresia most commonly seen in the foal?
colon
where in the dog is stenosis rarely seen?
the jejunum
where in the cow is stenosis rarely seen?
the jejunum
where in the lamb is stenosis rarely seen?
the colon
where in the cat is stenosis rarely seen?
the colon
describe and define blind diverticulum
its an outpocketing of the gut tube
often see diverticulum of yolk stalk - an outpocketing of intestine into patent yolk stalk
what do neuromuscular abnormalities usually involve and what are two examples of such conditions?
usually involve neural crest and enteric nervous system
two examples: megaesophagus and lethal white syndrome
what is a fistula?
an opening with another system
what are 3 examples of fistulas?
- tracheosophageal fistula - often accompanies esophageal atresia
- urorectal (rectourethral) fistula
- umbilical fistula
what happens in a urorectal (rectourethral) fistula?
- urorectal septum fails to complete development.
- fecal material gets into urogenital system.
- females may survive
- often accompanied by rectal atresia - always critical
what happens in an umbilical fistula?
entire yolk stalk remains patent, connecting intestinal lumen with opening at navel
what are two examples of hernias?
- omphalocele
2. umbilical hernia
what is an omphalocele?
failure of gut to return to abdominal cavity from umbilical cord; covered by amnion
what is an umbilical hernia?
gut returns, but then herniates again through defect in muscular wall around umbilicus; covered by amnion AND peritoneum
what is situs inversus?
- lateral transposition of viscera (right/left reversal)
2. often accompanied by “immotile cilia syndrome”
