My statement about "male to male" or "female to female" parts has nothing to do with gender or genitals. Men have thicker muscles, stronger tendons, more blood vessels and a different physiology than women. This is a very real issue in things like heart and lung transplants. 90% of the people on the heart transplant list are men, and men cannot use female hearts. Organ donors are split roughly 50-50; then you have to get into the tissue and blood type matching etc. Another example is female lungs don't fit into a male chest cavity. It works the other way as well, male hearts are not a good fit for female donors with a significant greater risk of rejection. Even kidneys, where the new kidney is inserted alongside the existing and the 'bad' organs left in the patient, need to be inserted into the same gender recipient as donor. The kidney thing shocked me. Kidneys sort of just sit there and if there was any organ that did not care about the size or gender of the recipient it should be kidneys. Article on hearts here Paper on Kidney gender mismatch here Composite tissue allotransplantation is fascinating. There is so much going on during the transplant and it all has to match and line up. The surgeries are long and done under a microscope to meld together the tiny blood vessels, stitch the tendons together and fuse the bones while preserving the channels for the bone marrow so that it does not die in the recipient.this does not have to be true. If there's enough donors, I can entirely see a market for transgender body-swap, which would have several advantages over current gender reassignment surgery - most notably working sexual organs of the desired gender (if everything goes well).