Hockenbury Discovering Psychology 5th txtbk

506 CHAPTER 12 Stress, Health, and Copingcorticosteroids(core-tick-oh-STAIR-oydz) Hormones releasedby the adrenal cortex that play a key role inthe body’s response to long-term stressors.immune systemBody system that produces specializedwhite blood cells that protect the body fromviruses, bacteria, and tumor cells.lymphocytes(LIMF-oh-sites) Specialized white blood cellsthat are responsible for immune defenses.psychoneuroimmunologyAn interdisciplinary field that studies theinterconnections among psychologicalprocesses, nervous and endocrine systemfunctions, and the immune system.Figure 12.4 The Immune System Yourimmune system battles bacteria, viruses,and other foreign invaders that try to setup housekeeping in your body. Thespecialized white blood cells that fightinfection are manufactured in the bonemarrow and are stored in the thymus,spleen, and lymph nodes until needed.of the stress- producing event. Selye (1976) found that the rapidly occurringchanges during the alarm stage result from the release of catecholamines by the adrenalmedulla, as Cannon had previously described.In the resistance stage, the body actively tries to resist or adjust to the continuingstressful situation. The intense arousal of the alarm stage diminishes, but physiologicalarousal remains above normal and resistance to new stressors is impaired.If the stress-producing event persists, the exhaustion stage may occur. In this thirdstage, the symptoms of the alarm stage reappear, only now irreversibly. As thebody’s energy reserves become depleted, adaptation begins to break down, leadingto exhaustion, physical disorders, and, potentially, death.Selye (1956, 1976) found that prolonged stress activates a second endocrinepathway (see Figure 12.3) that involves the hypothalamus, the pituitary gland, andthe adrenal cortex. In response to a stressor, the hypothalamus signals the pituitarygland to secrete a hormone called adrenocorticotropic hormone, abbreviated ACTH.In turn, ACTH stimulates the adrenal cortex to release stress-related hormonescalled corticosteroids, the most important of which is cortisol.In the short run, the corticosteroids provide several benefits, helping protectthe body against the harm caused by stressors. For example, corticosteroids reduceinflammation of body tissues and enhance muscle tone in the heart andblood vessels. However, unlike the effects of catecholamines, which tend to diminishrather quickly, corticosteroids have long-lasting effects. If a stressor isprolonged, continued high levels of corticosteroids can weaken important bodysystems, lowering immunity and increasing susceptibility to physical symptomsand illness. There is mounting evidence that chronic stress can lead to increasedvulnerability to acute and chronic diseases, including cardiovascular disease, andeven to premature aging (Robles & others, 2005; Segerstrom & Miller, 2004).Chronic stress can also lead to depression and other psychological problems(Hammen, 2005).Selye’s pioneering studies are widely regarded as the cornerstone of modernstress research (Cooper & Dewe, 2004). His description of the general adaptationsyndrome firmly established some of the critical biological links between stressproducingevents and their potential impact on physical health. But as you’ll see inthe next section, the endocrine system is not the only body system affected bystress: The immune system, too, is part of the mind–body connection.ThymusLymphnodesSpleenLymphnodesStress and the Immune SystemThe immune system is your body’s surveillance system. It detects and battles foreigninvaders, such as bacteria, viruses, and tumor cells. Your immune system comprisesseveral organs, including bone marrow, the spleen, the thymus, and lymphnodes (see Figure 12.4). The most important elements of the immune system arelymphocytes—the specialized white blood cells that fight bacteria, viruses, andother foreign invaders. Lymphocytes are initially manufactured in the bone marrow.From the bone marrow, they migrate to other immune system organs, such as thethymus and spleen, where they develop more fully and are stored until needed.BonemarrowLymphaticvesselsLymphnodesLymphocytes in Action In this colorenhancedphoto, you can see white bloodcells, or lymphocytes, attacking and ingestingthe beadlike chain of streptococcus bacteria,which can cause diseases such as pneumoniaand scarlet fever.