In the introduction to Chapter 15, we noted that the same hormone often acts on several types of body cells to coordinate specific physiological responses. And each cell in the body has multiple types of hormone receptors on its surface and in its cytosol; different hormones binding to these receptors can induce similar or dissimilar cellular responses. In this section, we consider how multiple hormones and signal transduction pathways interact, focusing on one of the most important physiological control systems: regulation of the body’s needs for the metabolites glucose and fatty acids. Defects in these pathways lead to major diseases, including diabetes and cardiovascular disease; obesity itself can lead to these and other diseases, with dire consequences for the individual and increasingly for public health.

Cellular responses to changes in other nutrients, which are largely reflected in alterations in gene expression, are covered in Chapter 9.