We model the following capabilities of the body:

• "Living" -- existing and changing over time
• Experiencing physical states (e.g., hunger, pain)
• Experiencing physiological and pathological processes, notably, disease and healing
• Responding to external interventions (drugs, surgery - but also food, lifestyle habits, etc.) whenever they may happen

Diseases are modeled as changes in key property values over time. For each disease, a set number of conceptual stages is established, and typical values (or ranges of values) for each property are associated with each stage. Values at the start or end of each stage are recorded explicitly, with values between stages being interpolated.

If the physiological causal chains underlying disease and healing are understood, they are incorporated into the model. If not, knowledge "bridges" encapsulate clinical observations.

In the gallery is a schematic representation of our disease model of Gastroesophageal Reflux Disease (GERD), which contains the central causal chains but, of course, not the level of detail needed to run the simulation (that would be too complex to represent in such a figure).