Katsuyu is my slug summon. She is quite comfortable with others and is used to transporting the injured on her back very carefully. She's been my ally for decades, we have a close bond. I can heal through her as a medium by giving her my chakra.

[ In fact, Tsunade's power is directly tied to Katsuyu's strength. Their connection with each other went a little beyond most summon-master relations. ]

Hmm... it sounds like this one jutsu we have. We normally just focus chakra on the afflicted area, but if you're skilled enough to can flow the chakra to less accessible places. We're able to heal internal injuries. However, this one jutsu, using a person's bodily medium like hair or blood, heals through that medium. It's a technique that requires extreme precision and calculations based on the medium you're using, as if you apply the wrong amount of concentration through a certain medium you could end up putting the patient in a coma. [ This was a risk that came with all healing. Still, Tsunade loved talking about medicine and healing arts. She wants to learn all she can for more jutsus later. ]