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Lecture 10

Study Questions for Lecture 10 Study question answers for lecture 10.

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McGill University
Biology (Sci)
BIOL 303
Dragana Miskovic

1. Which organ systems are affected by amphibian metamorphosis? Describe briefly the changes in these systems between larval and adult forms. What is initiating those changes? All changes are initiated by thyroid hormones thyroxin (T4) and triiodothryonine (T3). Travel through blood to reach larva. 2. How would you define ‘regionally specific development programs’ (=organ specific programmed response)? Give an example. There are different tissue responses and timing of expression of various derivatives of thyroid hormones. T3 or T4 hormones instruct limb bud muscles to grow and tail muscles to undergo apoptosis. Organ specific programmed response is when there is specific responses to thyroid horomone – tail transplanted onto trunk is still sensitive to apoptosis and re-absorption. 3. List and briefly describe three types of metamorphosis in insects. Insect metamorphosis involves the destruction of larval tissues and replacement by entirely different population of cells. Ametabolous- no larval stage, direct development Hemimetabolous- gradual metamorphosis Holometabolous- larva, pupa, adult 4. List and briefly describe three main types of imaginal cells in insects. What is their role in metamorphosis? Imaginal discs- form wings, legs, antennae, eyes, head, thorax, and genitalia Histoblast nests- form adult abdomen Imaginal cells within each organ-develop as larval organs degenerate 5. What are the four major regeneration mechanisms? Briefly (one sentence) describe each of them. Epimorphosis- dedifferentiation into an undifferentiated mass followed by respecification Morphallaxis- regeneration through re-patterning of existing cells Compensatory regeneration- intermediate form Stem cell mediated regeneration- regrowth of certain organs or tissues that have been lost (continual replacement of blood cells) 6. Salamanders can reconstruct a complete limb, if necessary. Which parts of the limb are getting reconstructed after amputation? How do we call this type of regeneration? It only forms those parts that are missing none other. It is called dedifferentiation, proliferation, and respecification. 7. Describe the process of limb regeneration in salamander. Right after amputation a plasma clot forms. After the surrounding epidermis covers the wound, wound epidermis. Wound epidermis is a single layer, it proliferates to form apical ectodermal clot. No scar formation and no dermal closure like in mammals. Under cap dedifferentiation and proliferation results in the regeneration blastema. Cell subsequently redifferentiate to form new structures. 8. What are the similarities between apical ectodermal ridge and apical ectodermal cap? What are the differences? (Define both of them first.) Apical ecotdermal cap require fgf10 9. What is the role of nerves in salamander’s limb regeneration? Apical ectodermal cap is necessary: mesenchyme intergral to regeneration of limbs. Nerves release factors that drive the proliferation of blastema cells 10. Explain the following statement: Blastema is heterogeneous population of restricted progenitor cells. Muscle cells only arise from old muscle cells and dermal cells only from old dermal cells.And finally, cartilage from old cartilage or dermal cells. Blastema cells retain their specification. 11.What are the major steps in mammalian liver compensatory regeneration? If a lobe from the liver is removed, it does not grow back; however, the remain tissue gets bigger to compensate for the lost lobe. It is regeneration by proliferation and no dedegeneration. Five type of liver cells divide to produce more of themselves, but they retain their function. After the removal of the lobe the Hepatocytes that are connected to one another do not respond to HGF (responsible for cells to return to cell cycle to produce of themselves). The trauma activates metalloproteases that digest the ECM this leads to the separation and the proliferation of hepatocytes. Liver stops growing at a certain size (unknown). There is a second line of rengerative ability through oval cells which are prognitive cell populations. They are activated once hepatocytes fail to regenerate the liver. 12.Define maximum life span. Define maximum life expectancy. Maximum life spa
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