## Hormonal Control in Mammals

12.1 Hormonal Regulation

The hallmark of vertebrate physiology is the fine control of physiological states by negative feedback systems. For this to be effective, there must be mechanisms to turn off operating processes and to turn on dormant processes. This requires that there be body-wide communication among system components that signals the state of operating processes. The coordinated interaction of the central nervous system and hormones is one of the most important mechanisms by which negative feedback is achieved. Hormones are chemicals that are transported long distances via the blood and that are capable of turning on and off processes occurring at the site of hormone action. This chapter describes a mathematical model of one of these feedback systems that causes the level of glucose in the blood to be regulated within relatively narrow bounds.

The model illustrates a number of principles developed in Part I. First, it demonstrates the trade-offs required in model construction to balance mechanistic realism against mathematical simplicity and the need to minimize data requirements. Because the model is relatively complex, this chapter also illustrates the utility of Forrester diagrams for model exposition. As the model structure is explicated, principles of quantitative model formulation are revisited when we introduce a new, flexible mathematical function for representing nonlinear biological processes. Finally, the use of models to address interesting, practical questions is illustrated here by investigating the effects of eating on the blood sugar levels of diabetic and obese medical patients. These simulations demonstrate the potential practical value of mathematical models for patient diagnosis and treatment.

### 12.2 Glucose and Insulin Regulation

It's inconvenient to have to eat continuously, Superbowl Sunday not withstanding. Eating, while generally an enjoyable experience, can interfere with other worthwhile activities, such as changing channels or escaping from predators. Moreover, with the exception of a few ungulates and laboratory mice in feeding experiments, a predator's

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## Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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