Hormonal Responses to Exercise

As presented in part, the fuels for muscular exercise include muscleglycogen and fat, plasma glucose and free fatty acids, and to a lesser extent, amino acids. These fuels must be provided at an optimal rate for activities as diverse as the 400 meter run and the 26 mile, 385 yard marathon, or performance will suffer. What controls the mixture of fuel used by the muscles? What stimulates the adipose tissue to release more FFA? How is the liver made aware of the need to replace the glucose that is being removed from the blood by exercising mus-cles? If glucose is not replaced, a hypoglycemic (low blood glucose) condition will occur. Hypoglycemia is a topic of crucial importance in discussing exercise as a challenge to homeostasis. Blood glucose is the primary fuel for the central nervous system (CNS), and without optimal CNS function during exercise, the chance of fatigue and the risk of seri-ous injury increase. Although blood glucose was used as an example, it should be noted that sodium, calcium, potassium, and water concentrations, as well as blood pressure and pH, are also maintained within narrow limits during exercise. It should be no surprise then that there are a variety of automatic control systems maintaining these variables within these limits. Presented an overview of automatic control systems that maintain homeo-stasis. This chapter expands on that by providing information on neuroendocrinology, a branch of physiology dedicated to the systematic study of control systems. The first part of the chapter pre-sents a brief introduction to each hormone, indi-cates the factors controlling its secretion, and discusses its role in homeostasis. Following that, we discuss how hormones control the delivery of carbohydrates and fats during exercise.

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