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=== Rexeneración ===
A [[ RegenerationRexeneración ( biologybioloxía)| Regenerationrexeneración]] indicatesindica thea abilitycapacidade tode regrowvolver a missingfacer cfrecer unha parte do corpo partperdida.<ref>Carlson, B.M. (2007) Principles of Regenerative Biology. Academic Press, Burlington MA.</ref> ThisIsto isé verymoi prevalentpatente amongstnas plantsplantas, whichque showpresentan continuousun growthcrecemednto continuo, ande alsotamén amongen colonialanimais animalscoloniais suchcomo asos hydroids[[hidroide]]s ande ascidiansas [[ascidias]]. ButPero mosto interestmaior byinterese developmentalpara biologistsa hasbioloxía beendo showndesenvolvemento iné thea regenerationrexeneración ofde partspartes inen freeanimais livingde animalsvida libre. InEn particular fourcatro modelsmodelos haveforon beenos themáis subject of much investigationinvestigados. TwoDous ofdestes thesemodelos haveteñen thea abilitycapacidade tode regeneraterexenerar wholeo bodiescorpo completo: a ''[[Hydra ( genusxénero)|Hydra]]'', whichque canpode regeneraterexenerar anycalquera partparte ofdo thepólipo polypa frompartir adun smallpequeno fragmentfragmento,<ref>Bosch, T.C.G. (2007) Why polyps regenerate and we don't: Towards a cellular and molecular framework for Hydra regeneration. Developmental Biology 303, 421-433.</ref> ande os vermes [[ planarianplanaria]] wormss, whichque canpoden usuallyxeralmente regeneraterexenerar bothtanto headsas and"cabezas" coma as tailscolas.<ref>Reddien, P.W. and Alvarado, A.S. (2004) Fundamentals of planarian regeneration. Annual Review of Cell and Developmental Biology 20, 725-757.</ref> BothAmbos ofos theseexemplos examplesdestes haveexemplos continuousteñen cellun turnovercontinuo fedrecambio bycelular [[stema cells]]partir de andcélulas nais e, atpolo leastmenos innas planariaplanarias, atpolo least some ofmenos thealgunhas stemdas cellscélulas havenais beense shownsabe toque beson [[ cellpotencia potencycelular| pluripotentpluripotentes]].<ref>Wagner, D.E., Wang, I.E. and Reddien, P.W. (2011) Clonogenic Neoblasts Are Pluripotent Adult Stem Cells That Underlie Planarian Regeneration. Science 332, 811-816.</ref> TheOs otheroutros twodous modelsmodelos showmostran onlysó a rexeneración distal regenerationdos ofapéndices, appendages.comom Theseson areos theapéndices insectde appendagesinsectos, usuallyxeralmene theas legspatas ofdos hemimetabolousinsectos insectshemimetábolos suchcomo aso the cricket[[grilo]],<ref>Nakamura, T., et al. (2008). Dissecting insect leg regeneration through RNA interference. Cellular and Molecular Life Sciences 65, 64-72.</ref> ande theos limbsmembros ofde [[ urodeleurodelos|anfibios amphibiansurodelos]].<ref>Simon, A. and Tanaka, E.M. (2013) Limb regeneration. Wiley Interdisciplinary Reviews-Developmental Biology 2, 291-300.</ref> ConsiderableDisponse informationdunha isconsiderable nowcantidade availablede aboutinformación amphibiansobre limba regenerationrexeneración andde itpatas isde knownanfibios thate eachcada celltipo typecelular regeneratesse itselfrexenera a si mesmo, exceptagás forno connectivecaso tissuesdos where[[tecido conectivo|tecidos conectivos]], onde therehai isunha considerable interconversioninterconversión betweenentre cartilage[[cartilaxe]]s, dermis[[derma]] ande tendons[[tendón]]s. InEn termstermos ofdo thepatrón patternde of structuresestruturas, thisisto isé controlledcontrolado bypor aunha re-activation ofreactivación signalsde activesinais inactiva theno embryoembrión. ▼
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Aínda se debate sobre a vella cuestión de se a rexeneración é unha propiedade "prístina" ou "adaptiva".<ref>Slack, J.M.W. (2013) Essential Developmental Biology. Chapter 20. Wiley-Blackwell, Oxford.</ref> Se é certo o primeiro caso, coñecendo mellor os procesos, podería esperarse conseguir mellorar a capacidade rexenerativa en humanos. Se é correcto o segundo caso, entón cada exemplo de rexeneración teríase orixinado por selección natural en circunstancias particulares de cada especie, polo que non se esperarían regrass xerais para o proceso.
▲[[Regeneration (biology)|Regeneration]] indicates the ability to regrow a missing part.<ref>Carlson, B.M. (2007) Principles of Regenerative Biology. Academic Press, Burlington MA.</ref> This is very prevalent amongst plants, which show continuous growth, and also among colonial animals such as hydroids and ascidians. But most interest by developmental biologists has been shown in the regeneration of parts in free living animals. In particular four models have been the subject of much investigation. Two of these have the ability to regenerate whole bodies: ''[[Hydra (genus)|Hydra]]'', which can regenerate any part of the polyp from a small fragment,<ref>Bosch, T.C.G. (2007) Why polyps regenerate and we don't: Towards a cellular and molecular framework for Hydra regeneration. Developmental Biology 303, 421-433.</ref> and [[planarian]] worms, which can usually regenerate both heads and tails.<ref>Reddien, P.W. and Alvarado, A.S. (2004) Fundamentals of planarian regeneration. Annual Review of Cell and Developmental Biology 20, 725-757.</ref> Both of these examples have continuous cell turnover fed by [[stem cells]] and, at least in planaria, at least some of the stem cells have been shown to be [[cell potency|pluripotent]].<ref>Wagner, D.E., Wang, I.E. and Reddien, P.W. (2011) Clonogenic Neoblasts Are Pluripotent Adult Stem Cells That Underlie Planarian Regeneration. Science 332, 811-816.</ref> The other two models show only distal regeneration of appendages. These are the insect appendages, usually the legs of hemimetabolous insects such as the cricket,<ref>Nakamura, T., et al. (2008). Dissecting insect leg regeneration through RNA interference. Cellular and Molecular Life Sciences 65, 64-72.</ref> and the limbs of [[urodele amphibians]].<ref>Simon, A. and Tanaka, E.M. (2013) Limb regeneration. Wiley Interdisciplinary Reviews-Developmental Biology 2, 291-300.</ref> Considerable information is now available about amphibian limb regeneration and it is known that each cell type regenerates itself, except for connective tissues where there is considerable interconversion between cartilage, dermis and tendons. In terms of the pattern of structures, this is controlled by a re-activation of signals active in the embryo.
There is still debate about the old question of whether regeneration is a "pristine" or an "adaptive" property.<ref>Slack, J.M.W. (2013) Essential Developmental Biology. Chapter 20. Wiley-Blackwell, Oxford.</ref> If the former is the case, with improved knowledge, we might expect to be able to improve regenerative ability in humans. If the latter, then each instance of regeneration is presumed to have arisen by natural selection in circumstances particular to the species, so no general rules would be expected.
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=== Metamorfose ===
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