To understand how physics faculty design and teach their Introductory Physics for Life Sciences (IPLS) courses, we analyzed interviews with faculty to learn about their ideas about their students. We focused specifically on the narratives faculty use to reason about their students as future professionals and how that related to their learning goals for such courses. We found that faculty reason about their students' needs when describing curricular design decisions in a range of ways, including with a strong sense of personal responsibility towards students' preparation, justification about what students have an interest in or will need in the future, and imagined relations between the faculty's self and professionals in the students' field of study. To better support physics faculty in teaching interdisciplinary physics courses, we aim to help faculty become more aware of their stances toward their students. This analysis suggests ways of broadening the narratives that faculty use to understand their life science students.