I am a physicist but I have always wanted to understand how my digestion takes place in as much detail as possible. I have no idea about books or reference on the subject of Gastro-intestinal and digestive physiology. Can you help me?
If you have no medical background at all, you will need a general text that teaches more than just digestive physiology. That is because you need to understand the function of other systems that have an influence over the digestive system (for example, the peripheral nervous system).
Here are a few good general references to get you started:
You can start by trying to read the digestive physiology chapters, and look up the knowledge you lack in other chapters.