Students then moved to computers, working in pairs using a STELLA model to see the effect of different glucose release rates on insulin secretion. When given the opportunity, they tried to see what level of glucose release over time the body could tolerate by keeping glucose release consistently high - the equivalent of consuming several cans of JOLT over a couple of hours. They were impressed with the body's ability to keep up. Once the role of the pancreas shifted to students, they developed a newfound reverence for the organ. "I wouldn't make a very good pancreas," one student remarked. The delicate balancing feedback system, imbued with delays, that exists to preserve homeostatic levels of insulin and glucose was becoming clearer to students. What crystallized this vision for them was comparing a healthy system to that of a diabetic. Here students were determining how much insulin is needed for a "patient" before a food is ingested. For example, if a diabetic patient wanted to eat an apple, and the apple contains a given amount of glucose, how much insulin should be taken prior to eating the apple? It was difficult enough for them to find the optimal level and injection rate of insulin when a diabetic was releasing glucose into the blood at a constant rate (which supports the diet recommendation that diabetics eat many small meals throughout the day instead of the cursory three). Once the diabetic was releasing glucose into the blood at varying rates over time, it became an arduous task to maintain homeostasis. Students were seeing how critical each adjustment is to maintain normal blood sugar in a person who has no built-in mechanism to control blood sugar. What we didn't have time for, but plan to include next year, is a final challenge for students: to develop an insulin pump that can continuously secrete insulin (like the pancreas), responding to ebbs and flows in glucose levels to more consistently maintain homeostatic levels of insulin and glucose than periodic injections of insulin.

Homeostasis is an abstract concept that some students have a difficult time visualizing. STELLA modeling provides a hands-on realistic manipulative that allows students to experience negative feedback and so homeostatic control mechanisms. Used as an introduction to homeostatic feedback mechanisms, STELLA modeling provides students with an enhanced level of understanding upon which teachers can build.