Hi Rosie,
I work with Bill Ryan at his school, Toward Harmony Tai Chi & Qigong. I ran your question by him, and this is what he said.
Tim is partially correct in that Dragon & Tiger is a meridian line qigong. It does not primarily work through the left and right side channels, which are located deep in the body. Rather, it works by stimulating the meridians which lie close the surface of the body. These are the same meridians that are used in acupuncture, and stimulating them can have effects deep inside the body, including in your internal organs. There are qigong sets that work with the particular meridians that correspond to the different organs of the body. However, the movements of Dragon & Tiger qigong stimulate broader pathways which include multiple meridians. It is designed to work your entire energetic system, including all your internal organs.
That said, certain movements in D&T do stimulate particular organs more strongly. For instance, movements 1 and 6 especially work with the liver and lungs, moments 3 and 5 with the kidneys, and movement 4 is particularly good for the heart. Bill mentions these correspondences in this you tube video:
https://www.youtube.com/watch?v=hBl72pEi6jc
I hope this is helpful, and best of luck with your practice.
Dan Winter