Transplantation to replace such diseased or defective tissue as corneas and hearts necessarily requires a dead donor; paired organs such as kidneys, or large or regenerating organs or tissues such as skin, bowel, lung, liver, or blood, can be donated by live donors (see blood transfusion). Skin autografts, employing skin from the patient's own body, are used to replace lost skin; autograft transplants are also done with bowel, bone, cartilage and other connective tissue, and ovarian tissue. Replacement skin for autografts is now also grown in laboratories, and autograft bladders have been laboratory grown and implanted. In 2008 Spanish surgeons implanted a trachea in which autograft tracheal and adult stem cells had grown over the connective tissue scaffold from a donated trachea. Bone marrow transplants can come either from a donor or from stored host bone marrow. Controversial fetal tissue implants have been used for some neurodegenerative diseases and experimentally for fetus-to-fetus transplants in certain genetic disorders. In addition to transplanted human tissues and organs, artificial parts ranging from heart valves to hip sockets are routinely implanted. See also heart, artificial.