  Diabetes is a chronic condition, considered one of the civilization diseases,
that is characterized by sustained high blood sugar levels. There is no doubt
that more and more people is going to suffer from diabetes, hence it is crucial
to understand better its biological foundations. The essential processes
related to the control of glucose levels in the blood are: glycolysis (process
of breaking down of glucose) and glucose synthesis, both taking place in the
liver. The glycolysis occurs during feeding and it is stimulated by insulin. On
the other hand, the glucose synthesis arises during fasting and it is
stimulated by glucagon. In the paper we present a Petri net model of glycolysis
and glucose synthesis in the liver. The model is created based on medical
literature. Standard Petri nets techniques are used to analyse the properties
of the model: traps, reachability graphs, tokens dynamics, deadlocks analysis.
The results are described in the paper. Our analysis shows that the model
captures the interactions between different enzymes and substances, which is
consistent with the biological processes occurring during fasting and feeding.
The model constitutes the first element of our long-time goal to create the
whole body model of the glucose regulation in a healthy human and a person with
diabetes.
