How do I hold back tears?

I will be attending training for Domestic violence hot line & crisis. I was asked if I were an emotional person. At the time I felt strongly about my answer which was no. I was concentrating so hard on wanting this position so I can help victims, that I didn't realize it, but that question plays a major role in crisis prevention. The truth is I cry on commercials, happy endings to movies, news editorials, sad endings, lost children, and Extreme Home Makeover. How can I overcome being so emotional at the time of need, when I need to be strong and supportive for the victims? What steps can I take to not get emotional along with the victim about the cirstances that will come before me?