The Tegument and Nutrition
- tapeworms absorb all their requited nutrients from the host, through the tegument
- don't have any digestive system at all - completely lost
- free-living ancestors did have a digestive system - but it is not needed in parasitic life-style
- the tegument is a living tissue with high metabolic activity
- the outer lining of the tapeworm has numerous finger-shaped projections called microtriches - these function to increase the absorptive surface area of the worm, much the same as microvilli do in human intestines
- tapeworms require a lot of carbohydrates - but can only absorb glucose and galactose
- also absorbed: amino acids, by active transport across the tegument, purines and pyrimidines by facilitated diffusion, lipids (method unknown) and vitamins (method unknown)
The tapeworm Diphyllobothrium latum can absorb so much vitamin B12 that it can cause pernicious anemia in its host.
This was featured in an episode of the television show House: http://en.wikipedia.org/wiki/Insensitive_%28House_episode%29
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