exam 4 GI system development Flashcards
time period of GI development
3-12 weeks
from what dermal layer do GI and respiratory come?
endoderm
from where does urogenital system originate?
mesoderm with distal most portion coming from endoderm
How does mesoderm expand between endoderm and ectoderm?
gastrulation
how does spherical nervous system form?
through dorsal folding of neural plate
how is tubular GI tract formed?
lateral folding of embryo, which results in pinching off of flat endoderm into a GI tube
What does GI tube form?
epithelial inner lining of the GI track
what does histogenesis of GI tube involve?
association of mesodermal cells around the endoderm GI tube to form the outer layers of the GI track
what are layers of GI track?
lamina propria, submucosa, and outermost layers
How do GI epithelial lining cells differentiate?
from a stem cell to the different specialized cell types of the crypts and villa
when does differential of epithelial cells happen?
in the fetal phase. it continues throughout adult life.
what is a crypt? villus?
crypt is a fossa. villus a process.
when does tubular gut begin to form? what happens with it?
at three weeks. induction of major digestive glands
when are primordial of liver, dorsal and ventral pancreas and trachea visible? what happens with that?
4 weeks. gut is mostly tubular. oropharyngeal membrane ruptures.
when is expansion and early rotation of stomach? what happens then?
5 weeks. intestinal loop begins to form. cecum and bile duct evident
when is intestinal loop prominent and rotation of stomach completed?
6 weeks. allantois and appendix appear; urorectal septum begins to subdivide cloaca.
when is herniation of intestinal loop? what else happens?
7 weeks. also, rapid growth of liver, fusion of dorsal and ventral pancreas; cloacal septation complete.
when is counterclockwise rotation of herniated int. loop?
8 weeks. recanalization of intestine, early penetration of parasympathetic neuronal precursors from cranial neural crest into gut.
when do epithelial types differentiate?
at nine weeks. the herniated gut returns to body cavity
when do villi appear in small intestine?
11 weeks, along with differentiation of goblet cells
by when do villi line entire intestine?
by week 16. includes colon.
by when are peyer’s patches seen in small intestine?
by week 20
first step of GI development
formation of gut tube (which is attached to the posterior body wall by the dorsal mesentery and to the ventral body wall by the ventral mesentery)
second step of GI development
development of a series of specialized regions of tube (stomach, SI, LI, etc.) Leads to one set of abnormalities.
third step of GI development
evagination of glands from gut tube (pancreas, liver, etc.) 2nd set of abnormalities.
what is gut tube developmentally divided into?
foregut, midgut and hindgut
derivaties of foregut
Pharynx, thoracic esophagus, abdominal esophagus, stomach, superior hall of duodenum (superior to ampulla of Vater)
derivaties of midgut
ineferior half of duodenum, jejunum, ileum, cecum, appendix, ascending colon, right two thirds of transverse colon
derivaties of hindgut
left one third of transverse colon, descending colon, sigmoid colon, rectum
what genes control the GI tract development?
Hox family
how does gut tube affect anatomy of abdominal cavity?
rotation of gut tube drags the dorsal and ventral mesentery with it.
where does stomach develop in relation to esophagus?
distal to it.
how does stomach rotate?
90 degrees to the right.
what forms as stomach rotates?
it drags the dorsal mesentery with it, and the omental bursa forms.
from where do liver and pancreas evaginate?
from foregut just distal to the stomach
how do blood vessels supply GI tract?
they grow through dorsal mesentery
what develops from the elongation of the duct from the foregut?
elongation of duct leads to developing liver, followed by evagination of the gall bladder from the Liver duct and subsequent evagination of the dorsal and ventral pancreas, each with their own ducts.
How do pancreas fuse?
ventral pancreas rotates (right turn) around the duodenum to fuse with the dorsal pancreas
to produce insulin, how many steps does it take from embryonic stem cells? adult stem cells?
8 embryonic. 4 adult.
how does 90 degree rotation of stomach affect liver, spleen and pancreas?
liver ends up on right side of abdominal cavity with spleen to left side and the pancreas being retroperitoneal.
what is falciform ligament of liver
ventral mesentery
small intestine development?
SI elongates and rotates 120 degrees counter clockwise around the axis of the superior mesenteric artery.
what happens to SI as it elongates?
it becomes herniated into the umbilical cord because abd. cavity has not expanded to its normal size to accomodate the faster lengthening intesting. The intestine laster retracts back to abd cavity.
how does rotation of SI affect LI?
it affects the distal positions of the GI tract, like LI. reposittioning of LI leads to cecum being intraperitoneal, ascending and descending colon being retroperitoneal, transverse and sigmoid colon being intraperitoneal, and rectum retroperitoneal.
what is formation of rectum/anus tied to?
division of hindgut and allantois and breakdown of cloacal membrane.
what are origins of anal canal?
hindgut and protodeum (epithelium of cloacal membranes. dual origins makes these regions have different blood and nerve supplies.
