ABSTRACT
This chapter argues that new principles arise to allow organs to work robustly, keep the right functional size and resist mutants. Robustness must involve additional processes beyond the minimal model's glucose-insulin loop. Glucose causes beta cells to secrete the hormone insulin that is carried by the blood to all tissues. In dynamical compensation, tissue size grows and shrinks in order to precisely buffer the variation in parameters. Insulin is sensed by receptors in the cells of many tissues, and instructs the cells in the muscle, liver and fat to take up glucose from the blood, reducing blood glucose concentration. Pregnancy decreases mom's insulin sensitivity and hence diverts more glucose for the growth of the fetus – in pathological cases placing the mother at risk for diabetes. The circuit has a negative feedback loop similar to insulin-glucose, but with inverted signs: PTH causes increase of calcium, and calcium inhibits PTH secretion.
