I can't speak for the introverts, as I am about as extroverted as they come. But I will say that we have both kinds of people in my med school class. I would say 75-80% are pretty extroverted.
I have to say, that having worked as a nurses aid in a hospital for quite a while, I would say that communication skills are extremely important for physicians. And I was honestly a bit concerned about how some of my classmates would fare when confronted with actually interviewing patients. One girl in particular seemed painfully shy, but in my patient interviewing small group sessions, I watched her interview real patients and actors, and she did fine. I was pleasantly surprised.
I guess what I'm trying to say is that as long as you are able to communicate WELL with people, you'll be fine. Remember that doctor litterally means teacher, and the most important part of your job will be helping your patients and their families to understand their situation. That doesn't mean you need to be an extreem extrovert, but it means you should be comfortable speaking to people, patients, groups of family member, and groups of other students and physicians (ie at rounds).
Good Luck, and (in case you haven't heard it enough) just be yourself at your interviews.
