Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

17.11 The Alarm Phase During the alarm phase, an immediate response to stress occurs. This response is orchestrated by the sympathetic division of the autonomic nervous system. In the alarm phase, energy reserves are mobilized, (mainly in the form of glucose) and the body prepares to deal with the stress-causing factor by “fight or flight” responses. Epinephrine is the primary hormone of the alarm phase, and its secretion accompanies a generalized sympathetic activation. The characteristics of the alarm phase include increased mental alertness, increased energy consumption by skeletal muscles and many other tissues, the mobilization of energy reserves (glycogen and lipids), changes in circulation, a drastic reduction in digestion and urine production, increased sweat gland secretion, and increases in blood pressure, heart rate, and respiratory rate. 17.12 The Effects of Hormones on Behavior Many endocrine functions are regulated by the hypothalamus, and hypothalamic neurons monitor the levels of many circulating hormones. Other portions of the CNS are also quite sensitive to hormonal stimulation. The clearest demonstrations of the behavioral effects of specific hormones involve individuals whose endocrine glands are oversecreting or undersecreting. Even normal changes in circulating hormone levels can cause behavioral changes. In precocious (premature) puberty, sex hormones are produced at an inappropriate time, perhaps as early as age 5 or 6. An affected child not only begins to develop adult secondary sex characteristics but also undergoes significant behavioral changes. The “nice little kid” disappears, and the child becomes aggressive and assertive due to the effects of sex hormones on CNS function. In adults, changes in the combination of hormones reaching the CNS can have significant effects on intellectual capabilities, memory, learning, and emotional states. 17.13 Agi g and Hormone Production The endocrine system undergoes relatively few functional changes with age. The most dramatic exception is the decline in the concentrations of reproductive hormones. Blood and tissue concentrations of several other hormones, including TSH, thyroid hormones, ADH, PTH, prolactin, and glucocorticoids, remain unchanged with advancing age. Although circulating hormone levels may remain within normal limits, some endocrine tissues become less responsive to stimulation. For example, in elderly individuals, smaller amounts of GH and insulin are secreted after a carbohydrate- rich meal. The reduction in levels of GH and other tropic hormones affects tissues throughout the body; these hormonal effects are associated with the reductions in bone density and muscle mass.

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