I disagree. I took the Anatomy and Physiology course this past year at BU and I used the 11th edition textbook when the 14th edition was the recommended textbook to buy. Of course, I'm not sure what the course is like taking it online at ACC. You should email your prof to see if the 8th edition will work just fine! The prof is the best person to answer your question IMO.
Between the three editions there was only minor changes, otherwise all the general information was in both. Not only did I have an older edition of the textbook that I used on a daily basis, but I ended up getting a fantastic mark in A&P. Regurgitating word for word on a test isn't the best method to study. Understanding the material will help you out in the long run, especially for a tough course like A&P. But if you stay on top of studying you should do fine!