Birth Mother Needs a Kidney

We see lots of cases where adopted persons need transplants and seek out birth family in the hopes of a match. I'm sure there have also been cases where a birth mother (or some other birth family member) has needed a transplant and has, therefore, sought out a child relinquished for adoption, though I don't have any particular case in mind.  I'm curious as to what people think about that scenario.  Do you feel differently about those two scenarios -- the relinquished child seeking a transplant from birth family vs. the birth family seeking a transplant from the relinquished child?

I ask because of a discussion in my Adoption Law class;  the issue was similar, but not the same.  Under Texas law, a relinquished child can inherit from and through birth parents who died without a will (only a handful of states allow such an inheritance).  A birth parent whose legal rights in the child have been relinquished or terminated cannot inherit from or through that child.

No one in my class thought that a birth parent should be able to inherit from a relinquished child.  But a number of students in my class thought the child also should not be able to inherit from birth parents.  Here are the arguments they advanced: Birth parents are legal strangers to the child.  It seems that the child is getting an undeserved windfall from actual strangers (but then explain why it's okay to inherit from Great-Aunt Mildred whom you've never met?!).  It would diminish the inheritance of any other heirs of the birth parent, including children who were not relinquished but were raised by the birth parent. It seems almost punitive, a "tax" on relinquishing birth parents.

(Of course, all of this applies only to birth parents who do not leave a will. A birth parent can leave money to anyone they like, including a relinquished child, or exclude anyone they want, including a relinquished child.)

More than the legal issues, I'm curious about what people think about what I'll call the "reciprocity" issue.  Should it flow both ways?  To the extent there are moral obligations or connections that can't be severed by law, should birth parents inherit from birth children to the same extent that birth children should inherit from birth parents?  Should it be acceptable for birth family to seek out birth children for kidney/bone marrow/whatever transplants to the same extent it is acceptable for birth children to seek out birth family for the same?