A living donor is one who decides to donate a pair organ or a segment of a single body which is not life-threatening to them. Only if the living donor is related by direct kinship, whether by blood, marriage or civil, is kidney donation a possibiltiy (because you can live with one kidney and we have two) and a segment of the liver (because it is regenerable) .
When it comes to bone marrow transplantation, which is a renewable tissue, the living donor may have no relationship to the recipient.
Organs and tissues that can be procured: