ch 22 pt 1

• what does the endoderm form in general?

  the epithelium of the gut and respiratory tubes
• what are the 3 early functions of the endoderm?

  1. induce the formation of several organs
  2. construct the linings of two tubes within the vertebrate body
  3. form the epithelium of several galnds
• what is the endoderm critical for instructing?

  the formation of the notochord, heart, blood vessels and brain
• buds from the digestive tube form the

  liver, gallbladder, and pancreas
• besides the digestive function, what else does the digestive tube do?

  a major coordinator of the immune system
• the respiratory tube forms as what and "bifurcates" into what?

  the respiratory tube forms as an outgrowth of the digestive tube and eventually bifurcates into the two lungs.
• name the region of the digestive tube anterior to the point at which the respiratory tube branches off

  pharynx
• where do the tonsils arise from? (as well as thymus, thyroid, and parathyroid glands)

  epithelial outpockets of the pharynx
• what are the two sources of endodermal cells

  1. primitive endoderm- forms the yolk sac
  2. definitive endoderm- intercolate into the primitive endoderm layer
• which transcription factor marks the endoderm in many species?

  sox17
• high levels of nodal induce sox17, while BMPs and FGFs act against nodal and specify the migrating cells to become mesoderm
• MG-HG cells-

  • midgut-hindgut
  • exposed to high levels of Wnts, BMPs & FGFs
  • generates the intestines
• PFG cells

  • posterior foregut
  • exposed to somewhat lower levels of the paracrine factors
  • precursors of the liver and pancreas
• AFG cells

  • anterior foregut
  • very low level of the paracrine factors
  • precursors of the lung and thryroid gland