Both organs and tissue can be transplanted, but there are some big differences.

Organs – heart, liver, kidney, lung, pancreas – must be used within hours or a few days of the donor’s death and must be handled in ways that keep them viable. They are tested extensively for germs, although some of the most conclusive take too long to be of use. The additional risk is considered small and acceptable because organs are used in lifesaving operations. Donors and recipients must be compatible tissue and blood types.

Organs are governed by a heavily regulated system run by the federal Health Resources and Services Administration.

Tissue – bone, skin, tendons, ligaments, heart valves, corneas – is removed from a cadaver, also shortly after death. Most tissues can be frozen for months and thawed when needed, allowing more time to test for disease. Blood-typing with the recipient is not necessary.

Tissue banking is a private enterprise, even though, as with blood and organs, its products start out as donations. The Food and Drug Administration is in charge of regulating tissue.

As for donating organs or tissue, signing a driver’s license or other document is simply an expression of intent. Permission still must be sought from the donor’s next of kin before organs or tissues are removed.