This effect gives vitamins and minerals plenty of time to absorb through intestinal walls, so they do not escape through waste. (healthyeating.sfgate.com)
They have teeth - like mouth parts that allow them to attach to intestinal wall where they feed off the host's blood. (blog.nhvnaturalpetproducts.com)
It's power to absorb nutrients decreases and the structure of the lining and intestinal wall changes. (2ndchance.info)