The Liverwort Lunularia cruciata from Botany photo of the Day website. I'd say if your liver looks like this you've got a pretty serious problem.
Wort derives from the Old English wyrt, which simply meant plant! It was often used in the names of herbs and plants that had medicinal uses, the first part of the word denoting the complaint, or area of the body, against which it might be specially effective.
Although some of these names were acquired because the plants actually did contain substances that helped others were acquired because the plant, or part of the plant, merely resembled part of the body. This relationship of plant form to function was based in the "Doctrine of Signatures" and probably had its basis in natural theology: "it was reasoned that the Almighty must have set his sign upon the various means of curing disease which he provided."
Examples include Spleenwort (thought to be useful in treating the spleen), Liverwort (thought to be useful in treating the liver), Toothwort (thought to be useful in treating tooth ailments0 and Lungwort (thought to be useful in treating pulmonary infections). There are also lots of examples where plant in some way resembled the symptoms of a disease. So, for example, Poplar or "Quaking Aspen" leaves were used for shaking or uncontrollable body movements (medically known as palsy).