Model block diagram. State variables are represented with circles, solid arrows represent mass transfers, while dashed arrows indicate stimulations. The model is here schematically represented: the path of ingested glucose (Mi) from the stomach (S) through duodenum (D) and ileum (L), and absorption in the plasmatic compartment (G) is along the central set of compartments (bottom-down). The insulin compartment (I) is on the bottom right of the figure, while the incretins (W and U) and DPP4 (P) are represented in between glucose compartments and insulin. Finally, on the left side, anti-incretin (A) and ghrelin (H) are represented. All the compartments are linked with dashed arrows, indicating stimulation of the entry rates or of the elimination rates, showing the relationship between state variables.