During exercise and exposure to extreme environments, the body is faced with tremendous demands that require a multitude of physiological adjustments. Energy production must increase and metabolic by-products must be cleared. Cardiovascular and respiratory function must be constantly adjusted to match the demands placed upon these and other body systems, such as those regulating temperature. While the body’s internal environment is in a constant state of flux even at rest, during exercise these well-orchestrated changes must occur rapidly and frequently.
As the body transitions from a resting to an active state, the rate of metabolism must increase to provide the necessary energy. This requires the coordinated integration of many physiological and biochemical systems. Such integration is possible only if all of the involved tissues, organs, and systems can efficiently communicate. Although the nervous system is responsible for much of this communication, fine-tuning the physiological responses to any disturbance in homeostasis is primarily the responsibility of the endocrine system
Control of hormone secretion must be rapid in order to meet the demands of changing bodily functions. Hormones are not secreted constantly or uniformly, but often in a pulsitile manner, that is, in relatively brief bursts. Therefore, plasma concentrations of specific hormones fluctuate over short periods of an hour or less. But these concentrations also fluctuate over longer periods of time, showing daily or even monthly cycles (such as monthly menstrual cycles). How do endocrine glands know when to release their hormones and how much to release?
The endocrine glands and their respective hormones are listed in table 4.1. This table also lists each hormone’s primary target and actions. Because the endocrine system is extremely complex, the presentation here has been greatly simplified to focus on those endocrine glands and hormones of greatest importance to sport and physical activity.