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BIOL 1F25 (223)
Lecture 20

Lecture 20

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Brock University
Daniel Glenday

Outline of Lecture 20 Gastrointestinal System I. Development of the gut tube A) Gut tube forms from folding of lateral edges of endoderm - Three regions (foregut, midgut, hindgut) and associated openings - Gut tube is embedded in mesentery, which suspends it in the coelom, both of splanchnic mesoderm origin B) Morphogenesis of gut tube derivatives occurs in weeks 4 through 12 - Pharynx and lung bud appear early - Esophagus: becomes occluded then vacuoles reopen it - Stomach and intestine: rotations needed to result in final location - Each region (fore-, mid-, hindgut) specializes in craniocaudal direction (see chart, p. 4) - Following this, there is cellular differentiation and innervation (NCCs), then maturation to final form C) Shh/Ihh is responsible for radial patterning of gut tube - Epithelium (endoderm): Shh/Ihh expr throughout gut except for pancreas area - Lamina propria / submucosa (mesoderm): Shh/Ihh activates Ptc and BMP4 and inhibits diffn of smooth muscle from mesenchyme - Smooth muscle layer (mesoderm): outer most layer - Posterior Hox genes induced by Shh plays role in regionalization - Reciprocal induction of endoderm by mesoderm also plays role in regionalization II. Liver Development - Functions: metabolic, detox, homeostasis, hematopoiesis, bile synthesis - Liver development starts as outgrowth of foregut endoderm - BMP2,4 from septum transversum mesenchyme (from lateral plate meso.) and FGF from nearby cardiac region induce hepatic fate; default is pancreatic fate, which occurs distally - STM induces hepatoblast from endoderm to invade the STM - STM and endothelium produce BMP, HGF, VEGF needed for liver bud morphogenesis - Hex is required; prox1 regulates E-cadherin necessary for migration - Liver function requires a close association with vasculature - Angioblasts limit region of hepatocyte growth, requiring the endothelial VEGF receptor, flk1 - Hnf’s control differentiation of hepatoblast into hepatocyte or cholangiocytes (bile duct cells), the two functional cell types of the liver III. Pancreas Developme
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