As Berkeman said, the human bodies are voluntarily donated to science. A lot of stuff comes from slaughterhouses (think cows eyes), but true, some things like frogs are rounded up and (let's say) "put down" for use in schools. You don't kill them though...
Also, not to be rude, but do you actually subscribe to one of these religions?
How does the Karma thing work (for you, if you believe in it) for say, a doctor who must learn and practice his skill on cadavers and animals before being able to act as a practicing doctor who helps people (or animals if he becomes a Vet) day in and day out?
Yea, but you can't learn to operate on living things without first practicing on the dead ones. I imagine it would be more of a karmic penalty to operate ignorantly on a live subject that had a chance at life and kill it by malpractice, than to practice first on already-dead or dying animals first in order to hone your skill so that you could save lives. Maybe not.
As for you, if you don't want to be a medical practitioner, and you really do subscribe to a religion which denounces the handling of dead creatures, then discuss it with your teacher/professor.