每日新GRE之阅读能力锻炼素材五

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这里是由KnightBM给您能带来的精选新GRE阅读能力提升素材分享贴五(From Scientific American)


Defense Mechanisms




When we find ourselves in situations that seem threatening, the hypothalamus (下丘脑：脑中位于丘脑下边的部分，其构成中脑腹部的主要部分，作用是控制体温，某些新陈代谢过程以及其一些下意识活动)—a structure that lies deep in the brain—sends out an alarm. This triggers two cascades of activity: a rapid response that releases one set of hormones and a more delayed one that releases a different set of hormones. Together these two lines of defense not only enable us to cope with acutely stressful situations but also prepare us for similar future situations by strengthening our memory of what we have just been through.



1 Rapid Response



The hypothalamus sends a signal along fibers of the sympathetic (交感神经) nervous system to the adrenal medulla (骨髓), located in the core of the adrenal gland just above the kidney. The adrenal medulla then releases the stress hormones adrenaline and noradrenaline, which prepare the body for a rapid fight-or-flight response. Energy reserves are mobilized; blood pressure and heart rate increase to better supply nutrients to the muscles; respiration increases so that more oxygen reaches the brain; natural painkillers are released preventively; and platelets（血小板）are activated to minimize blood loss in case of injury.



2 Delayed Reaction



Later the body releases another set of hormones from the hypothalamus, pituitary gland （垂体） and adrenal cortex（皮层）in sequence. First, corticotropin-releasing hormone (CRH), which is produced in the hypothalamus, travels along a special network of capillaries to the pituitary gland, an almond-size structure located near the base of the skull. There CRH triggers the release of another hormone, adrenocorticotropic hormone (ACTH), which travels to the adrenal cortex via the bloodstream and triggers the release of cortisol（皮质醇）—the most important human stress hormone.



Cortisol boosts the action of adrenaline and noradrenaline while at the same time preparing the body for a return to normal. It puts a damper（抑制作用） on the body’s inflammatory（煽动性的） and immune responses and promotes the transformation of nutrients into fats and glycogen（肝糖：糖原）, thereby replenishing spent stores of energy.

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