"Charming intestines. As the most powerful organ governs us" Popular science book, which describes in detail the human digestive system. The text in it is easy to digest, sometimes even funny. There is also an audio format.
From the same series, a book about the cardiovascular system - "Knock, knock, heart! How to make friends with the most tireless organ and what will happen if you don't." Unfortunately, I haven't read it yet. I hope it will be just as interesting.
The science of physiology deals with the general structure of the body and the processes that occur in it. You can read these works, because they are recognized as some of the best:
1) Human Physiology, edited by V.M. Pokrovsky.
2) Human physiology. In 3 volumes. Ed. R. Schmidt and G. Tevs
3) Normal human physiology. Tkachenko BI
If you are interested in the human structure at the cellular level and a little higher, then you will need to find books on anatomy, but here I am not strong. Good luck learning)