I think if one is looking for professional help along the lines of holistic treatment of depression, it's necessary to leave the mainstream medical system. People like Psychiatrists, Therapists, conventional Physicians, specialist MDs, are by definition NOT looking at whole-body health. I know some are, but probably a tiny minority.

I have found the most help from the likes of Herbalists, TCM docs, Naturopaths, and Functional Medicine MDs. They are not narrowly focused on certain organs or body systems, but rather the whole person.

I don't think depression can be confined conceptually to any part of the body or person. It is social, spiritual, environmental, biological, emotional, psychological, etc.

Anyway, enough pretentious rambling. I think the biggest driver for me is lack of healthy relationships and healthy human connection. And early life trauma. But I think there are physiological issues layered on top.