I am a retired board certified plastic surgeon.
The skin is the body's biggest organ. After weight loss, there can be a great deal of loose skin
and hanging tissues. This is best visualized with pictures and videos, not with words. It can take 6 to 18 months for massive weight loss skin to adjust. Other organs fat component can shrink. The fat collected in the abdomen and omentum the structure of the intestine
that stores the fat, leaves the muscle fascia layer loose and stretched out. This one page below connect to hundreds of pages, photographs, and movies demonstrating this question that trying to summarize the topic with a few words only offers so much. This is an issue bothering so many that i even built a forum for discussion of the emotions and issues of this topic. The non fat components of the remaining organs do not change much to my knowledge. I have yet to see comparison of kidneys, liver or spleen after weight loss. The main changes to the volume of the stomach come from the internal fat reserves i described.
Hope this helps,
michael bermant, M.D.