Fig. 1.

Concept diagrams illustrating systems biological (left) and integrative physiological views (right) about organismic responses to an environmental or internal perturbation. Objects in blue are measurable, and objects in green are conceptual. In the integrative physiology model, there is a negative feedback loop that keeps levels of the monitored variable within bounds. In the systems physiology model, because positive (solid lines) and negative relationships (dashed lines) are embedded in the network, homeostasis is an emergent phenomenon resulting from a pattern of activation (thick solid lines) and inhibition (thick dashed lines).