Chapter Outline

 Photo A shows a tadpole. Photo b shows a frog that has developed legs but still has the tail of a tadpole. Photo C shows a fully grown frog.
Figure 28.1The process of amphibian metamorphosis, as seen in the tadpole-to-frog stages shown here, is driven by hormones. (credit "tadpole": modification of work by Brian Gratwicke)

An animal’s endocrine system controls body processes through the production, secretion, and regulation of hormones, which serve as chemical “messengers” functioning in cellular and organ activity and, ultimately, maintaining the body’s homeostasis. The endocrine system plays a role in growth, metabolism, and sexual development. In humans, common endocrine system diseases include thyroid disease and diabetes mellitus. In organisms that undergo metamorphosis, the process is controlled by the endocrine system. The transformation from tadpole to frog, for example, is complex and nuanced to adapt to specific environments and ecological circumstances.

The study of the endocrine system has led to many medical advances. Now scientists have discovered a hormone that mimics the effects of exercise by regulating metabolism and fighting insulin resistance.// email address is being protected from spambots. You need JavaScript enabled to view it.:POP8oZwe@10/Introduction#footnote1">1 You can read more about this exciting discovery at the Science Daily website.