Scheme of the <i>in vivo</i> model.

<p>The pancreas releases at any given time a total quantity <i>J</i>(<i>t</i>) of insulin, sum of the amounts <i>J</i>_<i>n</i>(<i>t</i>) secreted by the single controllers (represented as circles), depending, for the <i>n</i>-th controller, on the threshold <i>B</i>_<i>n</i>(<i>t</i>) and on the potentiation level <i>D</i>_<i>n</i>(<i>t</i>). Insulin flows from the pancreas through the portal vein (<i>Q</i>₁ compartment) to the liver (<i>Q</i>_<i>i</i> compartments), from which a part of the hormone is lost. Insulin then reaches plasma (<i>I</i> is the plasmatic insulin compartment) and stimulates the uptake of glucose by tissues. Glycemia (<i>G</i> compartment) is raised by glucose hepatic production <i>k</i>₃ and high glucemias stimulate the production of insulin, closing the cycle.