13.+Cestodes - Cestodes (Tapeworms) Cestodes(Tapeworms)

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Cestodes (Tapeworms)
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•phylum  Platyhelminthes , class  cestoidea   all are parasitic in GI track of vertebrate hosts  flat, segmented worms composed of  •scolex  ( head )    suckers, hooks or grooves ( aid attachment contains nerves terminate in ganglia  neck region   metabolically active  site where new proglottids form •proglottids  ( segments ) together proglottids are referred to as  strobila   segments only contain nerves  no functional gut segments enclosed in specialized  tegument   Cestodes (Tapeworms)  Tegument : the protective outer body covering of helminths
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nutrient acquisition across tegument  membrane microvilli cover surface active transport to obtain nutrients  anatomically independent segments   common nervous system connects segments  emanates from cerebral ganglia in scolex    mating  within  segment is unusual  sperm transferred between adjacent proglottids  Proglottid Segments
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gravid  proglottids develop after mating  contains  100s to 1000s  of embryonated eggs   some species   proglottids exit  intact   some species   segments  disintegrate   eggs usually passed embryonated ( immediately infectious contain a hexacanth  larva referred to as oncosphere   eggs viable for weeks to months in soil  hatch in small intestine of intermediate hosts  onchosphere penetrates gut track  stage is ingested by definitive hosts  transforms into adult in lumen of small intestine Proglottid Segments Hexacanth : tapeworm larva having 6 hooks Oncosphere : tapeworm larva in egg casing Metacestode : larval stage prior to adult Gravid :containing eggs
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Cestode Replication Eggs (in environment)  ingested by intermediate host Muscle of intermediate host  (containing metacestodes) is  eaten by definitive host 1 st  host supports oncosphere  development  to cysticercus(i) , then metacestode(s)  in  muscle. Metacestodes released in stomach of  definitive host, migration to small  intestine, development of adults Intermediate host cattle – pigs - etc. Oncosphere : embryo form Cysticercus/i : larval form Metacestode : last larval stage Definitive host humans – dogs –etc. Worms are hermaphroditic ; segments from adults with eggs are  shed in feces.
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Adult tapeworms do not cause pathology in human intestine when humans are intermediate hosts, cestodes cause morbidity  
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Taenia saginata (Goeze  1782)
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•commonly referred to as “ beef tapeworm •one of largest parasites to infect humans ( 8-10 m long ) •lives in upper half of small intestine (
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This note was uploaded on 12/13/2011 for the course BIOSCI m143 taught by Professor Staff during the Fall '11 term at UC Irvine.

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13.+Cestodes - Cestodes (Tapeworms) Cestodes(Tapeworms)

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