51 Endocrine System Introduction

Maintaining homeostasis within the body requires the coordination of many different systems and organs. Communication between neighboring cells, and between cells and tissues in distant parts of the body, is done through either the nervous system or the endocrine system. The nervous system utilizes electrochemical impulses to regulate muscles and glands. These signals, carried by neurons, elicit responses in target cells within milliseconds. However, the duration of those responses is very brief unless neuronal signalling continues. The endocrine system regulates biological processes through the release of chemicals called hormones. Hormones are released into body fluids—usually blood, which carries these chemicals to their target cells, where they elicit a response. The responses elicited by hormones usually take several seconds to several days to occur, and the duration of the response can last just as long without further signalling. Unlike nearly instantaneous nerve impulses, hormones of the endocrine system can regulate functions of the body on longer time scales to maintain homeostasis.

The major function of the endocrine system is to participate in homeostatic feedback loops by acting as a means of communication between integrators and effectors, and sometimes acting as the sensor as well. Since the function of the endocrine system is to maintain homeostasis, there will be many system level examples at the end of this chapter. This is an excellent time to review the concept and formal structure of homeostasis:

The endocrine system is also involved with growth, development and adaptation. Within all of these changing processes, our bodies tolerate fluctuations within certain limits but still overall homeostasis needs to be maintained.

Common Dysfunctions of the Endocrine System

We feel the effects of changes in the endocrine system at various points in our lives. Hormone levels fluctuate during puberty, and even after we eat a meal. Common dysfunctions of the endocrine system include an inability to regulate glucose, called diabetes mellitus, and an inability to regulate calcium levels in the bones, which may lead to osteoporosis. Other common disorders of the endocrine system include over- or under-production of thyroid hormone (hyperthyroidism and hypothyroidism, respectively), which impacts energy metabolism. In this unit, you will learn about dysfunctions of the endocrine system and the downstream results of such dysfunctions.