You can Physiology PreTest Self-Assessment and Review 14th edition by Patricia J. Metting free in pdf format.
About Book
PreTest is the closest you can get to seeing the test before you take it
Great for course review and the USMLE Step 1! Physiology: PreTest asks the right questions so you’ll know the right answers. Open it and start learning what’s on the test.
– 500 USMLE-type questions and answers
– What you really need to know for exam success
– Detailed explanations for right and wrong answers
– Tested and reviewed by students who recently passed their exams
Note: PDF is converted from other format so style is good.