Great question!
I feel that a knowledge of anatomy both western and eastern is beneficial when doing healing work such as reiki. Not for diagnosis as we cannot do that, but for a general idea of what chakras effect what areas. Many people know the chakras but have no idea where the pancreas is located or spleen. Usui talked much about working over certain organs. If you don't know where to find them you can't use Usui's healing guide correctly.
I was an EMT for 15 years, took anatomy and physiology as well. Perhaps you can take a college a&p course locally or get a book about basic anatomy. I would also pick uip a book on meridians.
Hope this helps,
Tracey