The core principles of physiology are those that physiology students should understand and be able to use. We have ‘unpacked’ three of the most important core principles (Flow Down Gradients, Homeostasis and Cell-Cell Communications) into their component ideas and thereby articulated a conceptual framework for each. Physiology faculty at 2- and 4-year colleges, universities and medical schools were surveyed and asked to identify the importance of each of the component ideas; the result of our first survey on ‘Flow’ was reported last year. Amongst the >40 responses to our survey on unpacking Homeostasis, there was strong agreement on the importance of the first level of component ideas within the conceptual framework. For example, ~80% agreed that the component idea that “Homeostatic processes require a sensor” was essential to understanding this core concept, however, less than a third responded that sub-component idea ‘Sensory receptors may be in different, distant locations in the body’ was essential. We have also identified misconceptions associated with some core principles and linked these to our unpacked conceptual frameworks. We are using the conceptual frameworks and the misconceptions to develop a conceptual assessment of physiology (CAP) instrument (i.e., a concept inventory). Supported by NSF grant DUE-1043443.