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13.11: Stress and Its Effects • Survival depends on maintaining homeostasis • Factors that change the internal environment are potentially life-threatening • Sensing such dangers directs nerve impulses to the hypothalamus • This can trigger a loss of homeostasis 1 Types of Stress • Two types of stress: • Physical stress • Psychological stress 2 Responses to Stress Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Stress results from changes in the external environment Hormonal signals Neural signals Signals from sensory receptors Sympathetic impulses Hypothalamus Adrenal medulla Epinephrine and norepinephrine released CRH released Anterior pituitary Norepinephrine released Short-term “fight or flight” or alarm stage. • Blood glucose increases. • Blood glycerol and fatty acids increase. • Heart rate increases. • Blood pressure rises. • Breathing rate increases. • Air passages dilate. • Pupils dilate. • Blood flow redistributes. ACTH released Adrenal cortex Cortisol released Long-term adjustment or resistance stage • Increase in blood concentration of amino acids. • Increased release of fatty acids. • Increased glucose formed from noncarbohydrates—amino acids (from proteins) and glycerol (from fats). 3 4
