[Computer simulation of cell renewal systems]

This paper deals with a block diagram which describes the structure of the control of erythropoiesis by negative feedback loops. The model is transformed into an adequate simulation program using a special block-oriented programming language called ASIM (Analoge SIMulation). For both normal and diseased states of the blood forming process the dynamic responses of the erythrocytes and reticulocytes are simulated by a digital computer analysis. The computer simulation includes different forms of anemia caused by parameter variations as well as by structural alterations. Rising oscillations are obtained too in multiloop control systems containing complex paths with minor loops, which for example take into account the erythrocytic chalones. The described model shows that rising oscillations, that are unstable control loops, can be produced by changing the control-loop structure as well as by parameter changes. In case of malignant disorders such failures becoming effective in oscillations are discussed as parts of disturbed homoeostasis. The results of these studies obtained by simulation should especially stimulate scientists working in the fields of biology and medicine to new test series to verify the proposed hypothesis.