Cestodes

• Characteristics feature of a tapeworm:

  • Doros-ventrally flattened
  • scolex, strobila
  • sensory, muscle and lococmotory systems
  • tegument
• how long is taenia saginata (beef tapeworm): 4-12m
• how long are Taenia solium (pork tapeworm)?

  4-8 m
• How long are echinococcus granulosus (dog tapeworm)?

  3-6mm
• what makes the body plan of a tapeworm?

  scolex and strobila
• What is the scolex?

  anterior attachment organ
• What is the strobila?

  Segmented part of the body of a tapeworm that consists of long of proglottids
• which systems are reduced in a tapeworm?

  sensory, muscle and locomotory. There is no gut
• What is the metabolically active layer through nutrients are absorbed?

  tegument or body wall
• describe the tegument

  secretion and waste material exported
• scolex:

  small attachmet organ that possesses eith hooks and suckers or only suckers to attach to host tissue
• Strobila: chain of proglottids, can grow 15-30cm a day

  proglottids bud sequenctially from the neck behind the scolex
• proglottids: grow continuously from neck, new proglottids replace old: immature, mature, gravid (50,000 -100,000 eggs)
• What does the scolex of T.solium look like?

  4 larger suckers and rostellum containing double row of hooks
• what does the scolex of T.saginata look like?

  4 large suckers - no rostellum and rostellar hooks
• Describe the proglottids

  monoecious

  fertilisation can occur between proglottids of same or a different tapeworm
• what does monoecious mean?

  Monoecious means having both male and female reproductive organs in the same individual.
• What occurs to the proglottids after fertilisation?

  Fill with eggs and gravid proglottids break off the chain and pass out in faeces or can crawl through anal sphincter
• What is a gravid proglottid?

  Egg-containing segment of a tapeworm
• what is the structure of gravid proglottids of T.solium?

  7-13 uterine branches
• what is the structure of T.saginata gravid proglottid?

  15-20 uterine branches
• how can you visualise the primary lateral branches of the uterus?

  carmine staining
• why would you want to visualised the primary lateral branches of the uterus?

  Differentiation of species and used for diagnosis
• why can't eggs be used to identify species of tapeworm?

  They are morphologically indistinguishable
• How do cestodes absorb nutrients?

  From host intestine directly through the tegument
• How are nutrients absorbed?

  through specialised membrane transport systems:

  • microvillous projections (microtriches) increase tegument surface area (3-6 fold)
• what is the functional unit of the excretory system called?

  protonephridium
• Why are flame cells so called?

  Due to the beating cilia looking like a flickering flame
• How does excretory waste leave the tapeworms body?

  Cilia on flame cells generate a current leading to excess water containig nitrogenous waste forced into tubule and eventually out of tapeworm body via excretory pores
• what is essential for tapeworm survival in the host intestines?

  conservation of water and elimination of salts
• what are the definitive host of T.saginata and T.solium?

  humans
• what is a T.saginata?

  beef tapeworm
• what is T.solium?

  pork tapeworm
• How are tapeworms passed onto the intermediate host?

  Eggs are ingested by intermediated host
• What occurs inside the intermediate host?

  A larval stage called the oncosphere penetrates through the gut wall through the mucosa of the duodenum - passes into blood and encysts within tissues
• What is a cysticerus?

  a thick membrane or wall (embryophore) - forming a highly protective structure around the oncosphere
• How long can a cysticerci infective for?

  7-10 weeks and remain viable for several months
• What occurs when a cysticerci is ingested?

  The scolex evaginates (activated by bile) and attaches to intestinal wall and develops into adult tapeworm
• When is meat declared safe for human consumption?


  if only a few cysticerci and meat is frozen for at least 20 days
• when is freezing lethal to cysticerci?

  withstand 70 days at 0