Unit1
The Human complex
— A Never –failing Source of Wonderment
“ In my view, ” wrote Thomas Jefferson in 1814 , “no knowledge can be more satisfactory to a man that of his own frame, its parts, their functions and actions. ” Distinguished thinkers before and since Jefferson have held this belief, but curiously, it is not one that the average person wholeheartedly shares. Man’s attitude toward his own body—his single most precious possession—is decidedly ambivalent. At one and the same time he is fascinated by it and fearful of it, partly in echo of ancient taboos, partly in the conviction that the body is too complicated to understand.
“在我看来，”托马斯杰佛逊于1814年写道：“对人来说，没有什么知识会比了解自身的架构、部件、以及他们的功能和运动更能使他满足。”在杰佛逊前后的杰出思想家均持有这个观点，但激发人好奇心的是，这个观点并不为普罗大众所由衷地接受。人们对自己的身体（这个对他自身来说最为宝贵的财富）的态度其实是充满矛盾的。一方面，人们对身体感到非常着迷，另一方面，却又对其深感敬畏，这在一定程度上是受古代禁忌的影响，也在一定程度上反映了人们确信肉体过于复杂而难以理解。
The possible approaches to a study of the body are legion. To the cynic, the body is no more than a tenement of clay; to the poet, a palace of the soul; to the physician, an all-too-ailing hulk. The psychiatrist sees it as a housing for the mind and personality. The geneticist sees it as a perpetuator of its own kind. The biologist sees it as an organism which can alter the future as a result of the experience of the past.
研究人体的方法可谓纷繁多样。对愤世嫉俗者来说，人体贱如粘土陋室；对吟诗作赋者来说，人体尊如灵魂的宫殿；对内科医生来说，人体是脆弱多病的躯壳。精神病学家视其为理智和个性的居所。遗传学家当其为自我繁衍的机器。生物学家视其为能借过往的经验来改变未来的生命体。
All the specialized scientific views of the body are valid. All, however, must start from the same premise: an awareness of the body’s basic structure and functions—its anatomy and physiology. And the bedrock principle of our present understanding of the body is that all living matter is composed of cells basically similar in structure and function.
所有有关人体的专业科学的观点都是有依据的，然而，所有的这些都必须有同一个前提：那就是对研究人体的基本结构和功能的解剖学和生理学的认识。我们对身体的了解的基本原则是，所有生物都是由结构和功能基本相似的细胞构成的。
A Swarm of Tiny Specialists
Studies of the cell—what it is , what it does and how it reproduces itself —have revealed it to be a fantastically complex world in itself. One of the major wonders of the cell is the disparity between its minuteness and the prodigiousness of its activity. Each cell is so tiny that millions of them may be found in a half-inch cube of human body tissue. Yet each comprises an almost unimaginably busy chemical laboratory with a highly ordered division of labor.
关于细胞的研究——细胞是什么，它是干什么的和如何复制的——已经表明细胞本身就是一个令人难以置信的复杂世界。细胞的一大精妙之处在于其体积之微细与其活性之大之间的反差。每个细胞是如此渺小，以至于在一个半英寸立方体大小的人体组织中可能发现数以万计的细胞。然而，每个细胞都堪比一个繁忙到难以想象的并有着高度的分工的化学实验室。
The cell has two main parts: a nucleus, containing the genetic material deoxyribonucleic acid (DNA), and a surrounding semifluid cytoplasm. Bounding the cytoplasm is the cell membrane, which keeps the cell contents in and undesirable material out, yet permits passage of both proper nutrients and wastes. The nucleus—cell headquarters—governs the major activities of the cytoplasm; its finest hour, however, comes at reproduction time, when chromosomes containing DNA split. It is in the cytoplasm, that the cell’s day to day business is carried on. Each of its various components, or organelles, is a specialist of surpassing skill. One type breaks down the food given entry by the cell membrane and converts it into energy .Another provides the site for the synthesis of protein—along with reproduction, a major function of most cells. Another packages the manufactured protein for transport wherever needed in the body.
细胞有两个主要部分：含有遗传物质脱氧核糖核酸（DNA）的细胞核，以及周围呈半流质的细胞质。包围着细胞质的是细胞膜，它包含着细胞内容物,并将不需要的物质隔离在外，然而它允许营养物质和代谢废物通过。细胞核——细胞的控制中心——调控细胞质的主要活动；然而，它最美妙的时刻是当细胞分裂时，包含DNA的染色体分裂繁殖。细胞日复一日的工作是在细胞质中完成的。各种组件或细胞器，都是一个个卓越的技术专家。其中一个功能是分解从细胞膜进入细胞的营养物质，并将其转化成能量。另一个功能是提供蛋白质合成的场所——伴随着细胞复制的全过程，这是大多数细胞的主要功能。再一个功能是加工包装制造的蛋白质 ，并将其运输到身体所需的各个部位。
To operate efficiently, the cell thus requires specific help from the body as a whole: food to provide raw material for the release of energy, oxygen to help break down the food, water to transport inorganic substances like calcium and sodium. Once its needs are satisfied, the cell itself provides the intricate mechanism for maintaining the balance essential to keep it in kilter—in short, to keep the body alive and healthy.
为了工作的高效运行，细胞需要得到身体的特定的帮助，总的来说：食物提供可释放能量的原材料，氧气帮助分解食物，水用于运输无机物，比如钙、钠。一旦这些需要得到满足，细胞自身就会通过错综复杂的机制，来保持正常运作所必须的平衡确使身体处于正常状态——简而言之，就是保持身体的活力和健康。
Cells share certain common characteristics, but most of the body's cells develop specialized features and abilities. The cells that form bone collect calcium salts; these cells are locked together in solid chunks, immobile. By contrast, the white cells of the blood, which fight off invading bacteria, roam freely about the body. Other cells make special chemicals for the body's use—the hormones produced in the endocrine glands, or the digestive enzymes poured into the intestine from the pancreas. Still other cells form the incredibly thin membranes in the lung or kidney that permit the filtering or exchange of dissolved body fuels and wastes.
细胞拥有一定的共性，但是大部分的人体细胞具有他们特化的特征和功能。那些构成骨的细胞能沉积钙盐，这些细胞连锁成坚固而无活动能力的块状固体。相比之下，血液中那些可以抵抗细菌侵略的白细胞，却能在身体内自由流动。某些细胞能产生特殊的化学物质供身体使用——如内分泌腺产生的激素，由胰腺分泌并进入肠道的消化酶。还有些细胞在肺或肾脏形成非常薄的膜，使其能够过滤或交换已被溶解的身体燃料和废物。
According to their particular features and their intended functions, cells form different types of tissue: bone, muscle, blood, nerve tissue, connective tissue and epithelium. The cells that make up each of these are not identical, but belong together by reason of underlying similarities.
根据它们各自的特点和所要求的功能，细胞形成不同种类的组织：骨、肌肉、血液、神经、结缔组织和上皮组织。构成这些组织的细胞是不同的，但因潜在的相似之处而同属一类。
For example, the cells of bowel muscle are rounder and shorter than the long, spindly cells of leg muscle, yet both kinds contract forcefully when stimulated by a chemical or electrical impulse. The cells that make up bone tissue differ sufficiently to make brittle bone in one place and spongy, resilient cartilage in another, yet all store the salts which give bone its calcified structure. The loose network of cells that supports the fatty padding under the skin and the dense capsule of cells that holds the knee joint in place are both forms of connective tissue. All nerve cells, varied as they may be, receive and conduct electrochemical impulses. All blood cell, varied as they may be, float freely in a circulating fluid, plasma.
例如，肠道的肌纤维比腿部细长的肌纤维更圆、更短，但是当这两种细胞都受到化学或电刺激时，它们都会发生强有力地收缩。构成骨组织的细胞是有相当程度的不同，它们可以在一处形成脆骨，而在另一处形成疏松而有弹性的软骨；然而，所有的细胞能储存钙盐，使骨成为钙化的结构。支撑皮下脂肪的疏散网状细胞和维持膝关节在恰当位置的密集胶囊状细胞，都共同参与构成了结缔组织。尽管可能有所不同，所有的神经细胞都能接受并传导电化学冲动；尽管可能有所不同，所有的血细胞都能在循环流体—血浆中自由地漂浮。
The most versatile cells are those of the various kinds of epithelium. Forming the body’s external coating—the skin—epithelial cells protect things inside from things outside. They also form the lining of the mouth, stomach and bowel, the inner surface of blood vessels, and the membranes that permit the lungs to breathe and the kidneys to excrete. Over the cornea of the eye they become a sort of transparent windshield, to permit the free entry of light to the retina. Other epithelial cells secrete a protective mucus to keep intestines, lungs and nasal passages from drying out. Still others manufacture powerful hormones that regulate the body’s chemical reactions.
最万能的细胞是各种各样的上皮细胞。它们共同构成人体的外套—皮肤，上皮细胞保护皮肤里面的物质不受外界侵害。它们还构成口腔、胃黏膜、肠黏膜、血管内皮和参与肺呼吸以及肾排泄的膜。 覆布于眼角膜上的上皮细胞，它们变成一种透明的挡风玻璃，使得光束自由地进入到视网膜。其他的上皮细胞分泌保护性的粘液保持肠、肺和鼻腔不至于变干燥。还有一些上皮细胞能够产生高效能的激素来调节人体化学反应。
Interlock and Overlap
The tissues comprise the structural materials of the body’s organ systems. These, in turn, may be compared to a number of corporations with interlocking directorates. Indeed the interdependence of the organ systems has led to some disagreement over how many there are. The venerable Gray’s Anatomy—used by medical students for more than 100 years—lists 10 systems: nervous, digestive, respiratory, vascular, urogenital, endocrine, skeletal, muscular, joints and external covering. Other authorities categorize joints and bones together because they are so closely related, or separate the sense organs from the nervous system, or lump all the internal organs respiratory, digestive, endocrine and urogenital—under the resounding title of splanchnological system.
人体器官系统的物质结构由组织组成。换言之，这就像互相之间交叉任职的董事的若干公司。事实上这些相互依赖的器官系统在他们数量多少的问
题
快递公司问题件快递公司问题件货款处理关于圆的周长面积重点题型关于解方程组的题及答案关于南海问题
上也曾引发了一些争论。备受推崇的Gray解剖学-曾被被医学生使用了上百年的时间-列举出了十个系统：神经系统，消化系统，呼吸系统，血管系统，泌尿生殖系统，内分泌系统，骨骼系统，肌肉系统，关节和皮肤系统。而另一些权威人士则因关节和骨头是密不可分的而将他们归为一类，或是将感觉器官从神经系统分离出来，或是将所有的内脏器官-呼吸器官，消化器官，内分泌器官以及泌尿器官混在一块，冠以内脏系统这一声势浩大的名称。
Far more important than their labels is the fact that the systems interact; the breakdown of one can damage or destroy the others. Ideally, of course, all systems would do their jobs perfectly all the time. Unfortunately, nature permits no such perfection. All of them suffer from malfunctions at one point or another. The wonder is that breakdowns are the exception rather than the rule.
然而比给他们的命名更为重要的是他们各个系统之间会相互影响这个事实，其中一个系统的衰弱可以损害或毁灭其他系统。当然，理想状态下，所有的系统都是能一直完美地执行他们的任务的。而不幸的是，自然状态下是不可能出现这么完美的情况的。在所有系统当中，他们总会因这个方面或那个方面的故障而受到损害。神奇的是，出现故障倒是例外而不是常规情况
Within the healthy body itself there is no absolute criterion for "normal". Variations occur not only between individuals, but within the individual himself, sometimes from hour to hour, depending on his activity at the time. Doctors privately joke that even a baboon could get through medial school if he learned to say, with enough profundity, "It varies." One of the practitioner’s major headaches is to determine whether a patient’s condition reflects an actual illness or merely a variation within a broad range of normal. The breadth of this range may be indicated by a few statistics. The weight of the healthy heart is considered to be anywhere between 240 and 360 grams; the weight of the healthy liver, between 1,000 and 2,000 grams; the level of sugar in the blood, between 70 and 130 milligrams.
在健康的人体内对于“正常”也没有确切的
标准
excel标准偏差excel标准偏差函数exl标准差函数国标检验抽样标准表免费下载红头文件格式标准下载
可言。变化不仅仅发生在个体之间，也可以发生在个体内部，有时候每个小时都不同，这要看他们当时的运动状态。医生私下开玩笑说，即使是一个狒狒，它也可以在医学院校毕业，前提是他学会很深沉地说“因人而异”。令从医者最头痛的问题之一就是要确认一个人的情况是真正生病了还是处于正常的变化范围之中。有些范围内的波动可能是已经被一些统计资料所确认的。健康的心脏重量范围是240~360g，健康的肝脏重量在1000~2000g之间，血糖浓度水平是70~130mg。
Unit 2
Reading A
Human Anatomy
The human body is a remarkably complex and efficient machine. It takes in and absorbs oxygen through the respiratory system. Then the oxygen-enriched blood is distributed through the cardiovascular system to all tissues. The digestive system converts digestible food to energy and disposes of the rest. The skeletal-muscular system gives form to the body. And covering almost the entire mass is the skin, the largest organ of the body. The science of the structure of this complicated” machine” is called anatomy.
人体是一个非常复杂并且高效的机器。它通过呼吸系统吸入并且吸收氧气。然后这富含氧的血液通过心血管系统被分布到所有的组织。消化系统将能消化的食物转变成能量并且将剩余的废物排出。骨骼-肌系统组成了人体的轮廓。全身最大的器官——皮肤,几乎覆盖整个躯体。这门研究机体复杂构造的科学被称为“解剖学”
One of the major systems is the skeletal-muscular system. The body is supported and given shape by this structure, consisting of more than 200 bones and the muscles and tendons which are connected to them. They are strong but can bend at their joins. They also serve as a shield, protecting the vital internal organs from injury.
主要的系统之一是骨骼-肌系统。人体由这个结构作支撑并构成形态，这一结构由200多块骨和肌肉及与之相连的肌腱组成。它们很坚固但是能够通过弯曲关节。它们也能像防护物一样，保护内部重要的器官免受伤害。
Bones are as strong as steel but much lighter and more flexible. They are composed of minerals, organic matter, and water, held together by a cement-like substance called collagen, and are filled with red and yellow bone marrow. The red marrow produces the red blood cells used throughout the body to transport oxygen, while the yellow marrow consists of fat cells. A tough membrane called the periosteum covers most of the bone surface and allows bones to be nourished by blood.
人体的骨骼像钢铁一样坚韧但是骨骼更轻更柔韧。这些骨骼由矿物质，有机物，水构成---它们通过一种被称为胶原的类似结合剂的物质连结起来，并且充满了红骨髓和黄骨髓。红骨髓产生一种能够运输氧气到达全身各处的血红细胞，然而黄骨髓由脂肪细胞组成。有一种坚韧的膜被称为骨膜，它覆盖了大部分骨的表面，使骨头能得到血液的滋养。
A major bone structure in the body is the vertebral (spinal) column. It runs up and down the back and protects the spinal cord, where many of the major nerves are located. It is composed of bony vertebrae which are held together by ligament of connective tissue and separated from each other by spinal discs. At the top of the vertebral column is the skull, which surrounds and protects the brain. Attached to the vertebral column below the neck are the 12 pairs of ribs, comprising the rib cage. At the bottom is the sacrum, which connects the vertebral column to the pelvis. Bones are united by joints and held together by ligaments.
身体中一个主要的骨骼结构是脊柱。它贯穿人体背部并且保护脊髓，有很多重要的神经位于这里。脊柱是由属于结缔组织的韧带连接起来的椎骨组成的，并且相邻椎骨由椎间盘分隔开。在脊柱的顶部是颅骨，颅骨包裹并且保护脑。在颈部以下连着脊柱的是12对肋骨，共同构成了胸廓。脊柱的底部是骶骨，骶骨把脊柱和骨盆连接在一起。骨骼通过关节联合并且通过韧带连结。
Muscles are special fibrous tissues found throughout the body. They control movement and many organic functions by contracting in response to nerve signals. Skeletal muscles are called voluntary because they can be consciously controlled. They are attached to bones by tough fibrous tissues called tendons. Other muscles, such as the stomach muscled and the heart, are involuntary and are operated automatically by the central nervous system.
肌肉是遍布身体的特殊纤维组织。它们通过收缩来回应神经信号从而控制运动和许多器官功能. 骨骼肌能被意识控制，所以称为随意肌。它们通过一个叫肌腱的结实纤维组织紧紧附着于骨上。其他肌肉，例如胃肌和心肌，都是非随意肌，由中枢神经系统控制，自动运作.
The most important muscles in the body is the heart. Without the heart and its cardiovascular (circulatory) system, human life would not be possible. The heart is roughly the size of two fists. It contracts at an average rate of 72 times per minute or nearly 38,000,000 times a year. These rhythmic contractions are called the pulse rate and can be felt in the radial artery of the wrist.
心肌是人体最重要的肌肉，没有心肌和它的心血管循环系统，人类将不可能生存。心脏大概两个拳头那么大，平均每分钟收缩72次或接近38000000次每年。这种有节奏的收缩称之为脉搏, 并且可以在手腕的桡动脉处感觉到。
The human heart consists of four chambers ，two atria and two ventricles .Each is made up of several layers of cardiac muscles arranged in circles and pirals. During the contraction phase, called the systole, oxygenated blood is pumped out of the left ventricle into the aorta and from there through the arteries to all organs of the body. Carbon dioxide, a waste product of this process ,is collected in the blood. The blood is passed back to the right atrium through the veins and the vena cava during the diastole (or relaxation) period of the heart. From there, it is pumped into the right ventricle and to the pulmonary artery to be sent to the lungs where carbon dioxide is removed and oxygen is added.
人的心脏由四个腔室组成, 两个心房和两个心室, 每个腔都是由许多层心肌环绕，盘旋排列而成。（心脏）在收缩阶段，被称为收缩期，富含氧的血液从左心室泵出进入主动脉，然后从那里通过动脉运送到全身所有的器官。二氧化碳是这个过程中产生的废物，通过血液收集。血液在心脏舒张期通过静脉和腔静脉回流到右心房。从那，血液被泵入右心室并通过肺动脉被送到肺部，在那二氧化碳被移除，氧气被加入。
The rest of the system consists of arterioles (small arteries), venules (small veins), and capillaries, the smallest of blood vessels. In total, there are more than 70000 miles of blood vessels in the human body!
这个（心脏）系统的其余部分则是由小动脉，小静脉及最微小的血管——毛细血管构成，总的来说，人体中的血管长度远远超过70000英里！
The cardiovascular system also carries hormones which are secreted by glands of the endocrine system directly into the bloodstream. These hormones control many functions of the body. The thyroid gland, for example, secrets thyroxin ,which controls the rate at which energy is produced（the metabolic rate）.
心血管系统也参与运输一些由内分泌系统的腺体分泌且直接进入血浆的激素。这些激素控制身体的许多功能。例如，甲状腺分泌甲状腺素，这种激素控制着能量产生的速度（代谢率）。
The respiratory system starts at the nasal passage, where air is breathed in during inspiration. There the air is filtered and its temperature regulated. It passes through the larynx and trachea into the bronchi and bronchioles, and ends in little air pockets called alveoli within the lungs. The used blood is cleansed of carbon dioxide, which is expelled in the process known as expiration. The cleansed blood is then oxygenated and redistributed along the circulatory system. The entire process is called respiration and occurs at the rate of about 16 to 20 times per minute.
呼吸系统始于鼻腔通道，即吸气时空气进入的地方。在那里（鼻腔）空气被过滤，温度被调节。然后，空气通过喉和气管进入支气管和细支气管，最后进入肺部被称作肺泡的小气泡里面。被用过的血液清除二氧化碳并通过呼气过程排出。净化后的血液随后被氧化并且随着循环系统被重新分配。这整个过程称为呼吸，它发生的频率在每分钟16到20次之间。
The largest organ in the body is the outer covering called
Skin.(the average man about 20 square feet of it. ) The skin plus its associated structures (hair, nails, sebaceous and sweat glands, and specialized sensory receptors that enable the body to be aware of touch, cold, heat, pain, and pressure) make up the integumentary system. Skin protects the body from microbes and other impurities, prevents the loss of body fluids, and regulates body temperature. Three layers of tissue make up the skin-the epidermis, the dermis, and the subcutis (subcutaneous layer) The epidermis is in constant growth, with its outer layer of dead cells continuously being replaced as new cells are formed in the lower layer. Hair, fingernails, and toenails are specialized forms of epidermis. The coloring pigment called melanin is also found in the epidermis. The middle layer (or dermis) is the location for two main types of glands-sweat glands and oil glands. The innermost subcutis contains fat cells, blood vessels, and nerves.
人体最大的器官就是包裹在人体表层的皮肤（一般人的皮肤面积平均约为20平方英尺）。皮肤加上与之相关的结构（头发，指甲，皮脂腺和汗腺，以及专门能使身体感受触摸，冷，热，痛苦和压力的感受器）共同组成了皮肤系统。皮肤能保护机体免受微生物和其他杂质的伤害，防止体液流失，及调节体温。 三层组织组成皮肤--表皮，真皮，和皮下组织(皮下层)。表皮是在不断增长的，在表皮下层新形成的细胞会不断地替代外层死亡的细胞。头发，指甲和脚趾甲都是表皮的特化形式。在表皮中也发现了被称为黑色素的着色色素。中间层（或真皮层）是皮肤的两种主要腺体，汗腺和皮脂腺的所在地。 最里面的皮下组织包含脂肪细胞，血管和神经。
Another major body complex is the digestive system, which processes the food so that it can be used for energy. The process begins in the mouth, where food is chopped and crushed by the teeth. In the mouth, saliva, excreted by the salivary glands, provides enzymes that help to break down the food`s carbohydrates. This taking of food into the body for digestion is called ingestion.
另一个主要的身体复合体是消化系统，该系统对食物进行加工处理，以便食物能被作为能量使用。该过程开始于口腔，食物被牙齿嚼碎和粉碎。在口腔里，由唾液腺分泌的唾液提供的酶有助于分解食物中的碳水化合物。这种为了消化而获取食物进入身体称为摄入。
After food has been chewed, it passes through the esophagus into the stomach. Peristaltic movements in the walls of the esophagus help push the food along the alimentary canal. The muscular walls of the stomach continue the mixing process while secreting hydrochloric acid from the glands in the stomach lining. After 30 minutes to three hours in the stomach, the food is converted into a semiliquid state and passes into the small intestine, a tube about 20 feet long located in the lower abdomen. Here, enzymes from pancreatic fluid and bile from the liver complete the digestive process. Nutrients are absorbed into the blood through the villi, which line the walls of the digestive organs. What cannot be absorbed is passed out through the large intestine as feces. Liquid wastes are eliminated through the urinary system. They are picked up by the blood and removed by the kidneys. From there they pass through the ureter, bladder, and urethra, and are excreted from the body as urine.
食物被嚼碎后经过食管进入胃。食道壁的蠕动有利于把食物推向消化道中。胃壁肌肉在此过程继续搅拌同时盐酸从胃粘膜中的腺体分泌出来。在胃里经过30分钟—3小时，食物转换成半液体状态，进入小肠，一条长约20英尺长，位于下腹部的管道。在这里，来自胰液的酶和来自肝脏的胆汁完成消化过程。 营养物质通过排列于消化器官壁的绒毛被吸收进血液。那些不能被吸收的作为粪便通过大肠被排出。液体废物通过泌尿系统被消除。它们被血液带走，然后被肾移除。从那里它们再经过输尿管，膀胱，和尿道，然后以尿的形式从身体排出。
Closely associated with the urinary system is the reproductive system，by which human life is carried on to future generations. Sperm cells are produced in the testicles of the male and ejaculated through the penis into the female vagina. The fertilization of the female’s ovum (egg) by the male’s sperm is called conception. It usually occurs in one of the fallopian tubes, which the sperm reaches through active movement from the place of deposition. Normally, the fertilized egg then travels to the uterus where it becomes an embryo, is implanted, and develops for about 280 days (until childbirth）.
与泌尿系统紧密联系 的是生殖系统，通过生殖系统人类生命得以世代延续。精子细胞在男性睾丸里产生，并通过阴茎射精进入女性阴道。女性的卵子与男性的精子结合叫做受精. 受精通常发生在其中一条输卵管中，精子从存放处通过主动的运动到达输卵管。在正常情况下，受精卵接着游移到子宫，在此植入并变成胚胎，然后发育约280天左右（直至分娩）。
The nervous system controls all other systems and bodily movements. Nerves carry sensory impulses to the central nervous system and motor impulses from the central nervous system. Most impulses are those that control muscles. Sensory impulses affect the senses that enable human beings to feel, see, taste, and so forth.
神经系统控制着其他所有系统和身体运动。神经将感觉冲动传至中枢神经系统，并将运动冲动从中枢神经系统传出。大部分运动冲动控制着肌肉，而感觉冲动影响感官，这些感官能使人类去感知，去看，去品尝等等。
The nervous system is divided into the central nervous system (the brain and spinal cord) and the peripheral nervous system, which consist of the nerves that connect muscles and sensory organs with the central nervous system. The central nervous system is responsible for sending impulses to the voluntary muscles. The autonomic system, a part of the peripheral nervous system, regulates the involuntary muscles and organs
神经系统分为中枢神经系统（脑和脊髓）和周围神经系统，包括把肌肉和感觉器官与中枢神经系统连接起来的神经。中枢神经系统负责把冲动传递给随意肌。 自主神经系统即周围神经系统的一部分，调节不随意肌和器官。
The brain is not only the most important component of the nervous system; it is also the controller of all bodily activities, thoughts, and emotions. It is composed of the pons, medulla oblongata, cerebellum, and cerebrum. The cerebellum is the area of the brain that coordinates the voluntary muscles; the medulla oblongata controls the involuntary muscles; the pons is where many important nerves originate.
脑不仅是神经系统中最重要的组成成分，而且是躯体活动、思维和情感的控制者。它由脑桥、延髓、小脑、大脑组成。小脑是脑中协调随意肌的部位，延髓控制不随意肌，脑桥是许多重要神经的起源处。
It is the cerebrum that gives humans their ability to think, remember, and conceptualize. It is divided vertically into two halves known as the right and left hemispheres. The left hemisphere processes verbal functions, while the right hemisphere is involved in nonverbal activities and is the seat of human creativity. Many scientists believe that, in each individual, one of the two hemispheres is dominant, and that the individual has greater intellectual strength in the dominant hemisphere.
正是大脑赋予了人以思考，保持记忆和形成概念的能力。它纵向可分为左右两个半球。左半球处理语言功能，而右半球涉及非语言活动并且它是人类创造力的所在地。很多科学家相信，在每个个体的两个大脑半球中有一个占优势的，并且那个占有优势的大脑半球有较大的智力潜能。
It is amazing how well each system functions and coordinates with other systems to enable humans to live, reproduce, and create.
令人感到神奇的是每个系统的功能以及各个系统之间的协调配合，使人类得以生活、繁殖和创造。
Unit3
Body defense mechanisms
Although all pathogens pose potential threats if they gain entry to the body, the chances of this occurring are actually quite small. They must first overcome a number of effective barriers, many of which were established in the body prior to birth.
尽管所有的病原体如果进入到身体后都会造成潜在的威胁，但实际上这个情况发生的可能性是非常小的。它们必须先克服一系列有效的屏障，其中许多是在出生之前就已经建立的。
The skin and body linings
The first of these barriers is the skin itself. In order to penetrate through the outer layer of skin, the pathogen must first survive the acidity of the skin, which normally destroys most forms of bacteria. Tears, saliva, and perspiration contain chemicals that kill bacteria. Even if the organism survives this initial line of defense, it must then find a route of entry through hair follicles, breaks in the skin due to injury, sweat glands, or normal body openings. Having gained initial entry, the pathogen must then escape the internal mucosa of the body linings. This mucosa is a constantly moving, sticky mass that traps organisms, much like flypaper. Cilia, tiny hairlike projections that move in a sweeping action toward body cavities attempt to sweep offending microorganisms toward areas where they can be eliminated. Pathogens that survive these initial barriers reach the stomach, intestines, or other internal areas(depending on where they gained initial entry) and usually are destroyed. Those that are not destroyed by the body’s first line of defense must then deal with an even more powerful additional line of defense.
这些屏障中的第一个就是皮肤。为了穿透皮肤的外层，病原体必须首先经受住皮肤的酸性，这酸性通常会摧毁细菌的大部分形态。 眼泪、唾液和汗液包含能杀死细菌的化学物质。即使这个微生物能够幸免于这初始的防御线，它接下来必须从毛囊，受伤造成的皮肤伤口，汗腺或正常的人体开口中找到一条进入体内的通道。 一旦进入身体，病原体必须避开衬于体腔的内粘膜。这黏膜不断地移动，就像苍蝇纸一样作为黏性物质困住微生物。纤毛——以摆动方式朝体腔方向运动的细微毛发状突起——试图将引发不适的微生物扫向可以清除它们的区域。病原体一旦幸免于这些开始的屏障进入胃，肠或者其他内部区域（这主要决定于它们获得初始入口的地方）通常会被摧毁。 那些通过身体的第一道防线而没有被摧毁的病原体接下来必须解决一个更加强大的另外的防线。
Body fluids/cells
Whether threatened by an invading organism, a physical object, or a chemical irritant, the body reacts in a similar way to defend itself. The blood supply to the area increases, bringing more oxygen-carrying red blood cells known as erythrocytes to the area. Specialized white blood cells known as leukocytes rush to the site of infection to fight the invading organism. Another type of white blood cell that is particularly effective in projecting the body, especially against bacterial infections, is the phagocyte. Meaning” cells that eat,” phagocytes rush to an infected area, engulf the invaders, and digest them. This white blood cell activity is often signaled by phylogenic (pus-forming) buildup at the site of infection. In addition to cell activity, various enzymes and compounds in the blood itself can kill an infectious organism by causing it to break open, destroying its cell wall, or preventing it from multiplying.
不管威胁是来自入侵微生物、异物，还是化学刺激物，人体都以类似的方式作出反应以自我防卫。一个区域的血量供应增加，更多携带氧气的被称为红血球的红细胞将被输送过来。特化的白细胞被称为白血球，它们冲向感染区去对抗入侵的微生物。其他种类的白细胞能特别有效的保护身体，尤其能抵抗细菌感染的细胞是吞噬细胞。意思为“细胞吞食”的吞噬细胞冲向感染区，吞没入侵者，然后消化它们。这种白细胞的活动经常被感染区化脓物的积累所表明。除细胞活动外，血中的各种酶和复合物可通过使其破裂、摧毁细胞壁或阻止其繁殖等手段来杀死感染的细菌。
Fever
If the infection is localized, pus formation, redness, swelling, and irritation often occur. These symptoms indicate that the invading organisms are being fought systematically. Another indication is the development of a fever. (Normal body temperature is 98.6F.)Fever is often caused by toxins secreted by the pathogens that interfere with the control of body temperature. Although this elevated temperature is often harmful to the body, it is also believed to act as a form of protection. Elevations of body temperature by even 1 or 2 degrees provide an environment that destroys some types of disease-causing organisms. Also, as body temperature rises, the body is stimulated to produce more white blood cells, which destroy more invaders.
如果感染已经局部化了，脓的形成、红肿还有刺激会经常发生。这些症状表明这些入侵微生物已经被系统地进攻。另一个迹象是发烧。（正常的体温是98.6F。）发烧经常由致病菌所分泌的、干扰体温控制的毒素引起。体温升高虽对身体有害，但被视为一种防卫作用。体温仅升高1-2度就能提供摧毁某些致病菌的环境。并且，当体温升高时，身体受到刺激会产生更多的白细胞来摧毁更多的入侵者。
The immune system
If the above systems are breached, the body turns to its most powerful line of defense, the immune system. Immunity is the state of being resistant to injury, particularly by toxic chemicals, foreign substances, or parasites. When the body is invaded by one of these agents, it responds by forming substances that harm or destroy the invaders. Substances that invade and cause an immune response are called antigens. The body recognizes both the size and the shape of an invading antigen and produce specific antibodies that work to destroy or lessen the effects of the antigen. Antibodies work only on the specific antigens that activate them. Flu antibodies work on flu antigens, measles antibodies work on measles antigens, and so on.
如果上述系统遭破坏，身体就会求助于它最强大的防线---免疫系统。免疫力是机体抵抗伤害的一种体现，这种伤害特别是有毒化学物质，外来物质或寄生虫的伤害。当身体被上述其中一种物质入侵，免疫系统会产生伤害或破坏入侵者的物质而产生免疫应答。外来入侵物质以及引起免疫反应的物质被称为抗原。机体识别入侵抗原的大小和形状，并产生破坏或减轻抗原的影响的特异性抗体。抗体只对刺激它们的特异性抗原起作用。流感抗体对流感抗原起作用，麻疹抗体对麻疹抗原起作用，等等。
Regardless of the bodily reaction, the immune system generally is a powerful and effective ally in the effort to prevent disease. In each of the above instances, it is the white blood cells that are the operative protecting agents. The lymphocytes are white blood cells found in the circulating blood, lymph nodes, bone marrow, and certain glands. Two forms of lymphocytes in particular, the T-lymphocytes and B-lymphocyte, are involved in the immune response.
不管身体反应如何，免疫系统总的来说在防御疾病方面是一个强有力且高效的联盟 。在上述各实例中，白细胞正是关键保护剂。淋巴细胞是白细胞的一种，它存在于循环血液、淋巴结、骨髓和某些腺体中。尤其两种形式的淋巴细胞----T细胞和B细胞，都参与免疫反应。
Although white blood cells and the antigen-antibody response generally work in our favor by neutralizing or destroying harmful antigens, this is not always the case. Sometimes the body makes a mistake and targets its own tissue as the enemy, builds up antibodies against this tissue, and attempts to destroy it. When this occurs, an autoimmune(auto means “self”) disease occurs. One common example of this type of disease is rheumatoid arthritis.
虽然白细胞和抗原-抗体反应通常是通过中和或破坏有害抗原来保护我们，但是这并非总是如此。有时机体会出错，把自身组织当为敌人，产生抗体攻击这些组织并且要破坏它们。这种情况发生时，自身免疫（auto意思是“自己”）疾病就产生了。这种类型的疾病一个常见的例子是类风湿性关节炎。
In some cases, the antigen-antibody response completely fails to function. The result is a form of immune deficiency syndrome. Perhaps the most dramatic example of this was demonstrated in 1984, with the death of the “bubble boy”, a youngster who lived his life inside a protected environment because exposure to the outside world would have proved fatal. An even more frightening example of an immune system disorder is the epidemic of acquired immune deficiency syndrome (AIDS)
在某些情况下，抗原-抗体反应彻底失效。其结果其实是体现为一种免疫缺陷综合征。也许这方面最令人印象深刻的例子是1984年的“泡泡男孩”之死；由于一暴露在外面的世界就会致死，这个男孩一直生活在严密受保护的环境中。 一个免疫系统紊乱更可怕的例子是获得性免疫缺陷综合征这种流行病（AIDS）。
Each of the above defense mechanisms may be considered to be part of our natural immune system. To varying degrees, this natural defense mechanism is our strongest ally in the battle against disease, being with us from birth until death. There are periods in our life when the invading organisms are too strong or our own natural immunity is too weak to protect us from “catching” a given disease. It is at that time that we need outside assistance in developing immunity to an invading organism. This assistance generally is given in the form of a vaccination, which consists of killed or weakened organisms, given orally or by injection. This form of artificial immunity is termed acquired immunity, as compared to natural immunity.
上述的每一种防御机制都可以认为是我们机体先天的免疫系统的一部分。从某种程度上来说，这种天生的免疫系统是我们在与疾病的战斗中最强的盟友，伴随我们直至我们死亡。在我们的生命中总有那么几个时候，侵入的病原微生物太强或者我们的先天免疫太弱，以至于先天免疫系统不能保护我们面授疾病的侵害。在那个时候，我们就需要外来的协助来增强我们的免疫以对抗外来病原微生物。这种“协助”通常以接种形式—即口服或注射包含了已杀死的或者减弱了毒性的病原微生物—来实现的。这种人工的免疫区别于“先天免疫”被称为“后天免疫”。
Vaccines: living versus nonliving
In response to a deadly polio epidemic of the 1950s, scientists produced two major vaccines. The first of these, developed by Jonas Salk in 1954, contained killed organisms that stimulated antibody production against poliomyelitis (polio).People given this vaccine did not actually develop the disease, but, because they exposed themselves to the organism, their own bodies were able to produce antibodies to protect against later exposure to living polio organisms. Although the Salk vaccine was tremendously effective, the oral vaccine developed a few years later by Albert Sabin, which consisted of weakened (attenuated) polio organisms produced in the laboratory, provided an even more powerful means of stimulating antibody production. Some pathogens, such as tetanus, cause disease, through the toxins they produce. By modifying these toxins, toxoids can be formed that also stimulate antibody production and thereby prevent disease.
Today, depending on the virulence of the organism, vaccines containing live, weakened, or dead organisms are given to people for a variety of diseases. In some instances, if a person is already weakened by other diseases, giving a vaccination may provoke an actual case of the disease. This was what happened with the smallpox vaccinations that were given routinely in the 1960s.It was believed that the risk of contracting smallpox from the vaccine was actually greater than was the chance of getting the disease in an environment where it was essentially eradicated .For this reason, routine smallpox inoculations were eliminated in the late 1960s.
为了应对二十世纪五十年代流行的致命的脊髓灰质炎，科学家生产了2种主要的疫苗。第一种疫苗是在1954年Jonas Salk所开发的。疫苗包含了灭活了的病原微生物，这些灭活了的病原微生物能够刺激机体产生抗体对抗脊髓灰质炎。人们接种了这种疫苗以后实际上并没有患病。但是，因为他们暴露在微生物中，他们自己的身体能够产生抗体去对抗之后接触到的脊髓灰质炎病原体。尽管Salk的疫苗异常地有效，几年后一些口服的疫苗也被Albert Sabin 开发出来。这些疫苗由在实验室里削弱过的（已灭活的）脊髓灰质炎病毒组成，提供了一个更强力的刺激抗体产生的手段。一些病原体，比如破伤风杆菌，是通过他们自身分泌的毒素致病的。通过修饰这些毒素，能够形成刺激抗体产生的类毒素，从而预防疾病。今天，根据微生物的毒性，疫苗包含了活的，灭活的或者已经死掉的微生物会根据各种各样的疾病而接种给人们。在一些案例中，如果一个人已经因为其他疾病而身体虚弱的话，给他们接种疫苗可能会引起一场真正的疾病。这就是在二十世纪六十年代常规天花病毒疫苗接种时所发生的事件。很多人认为，从疫苗感染天花病毒的风险实际上比从病毒几乎被根除了的环境中患病的机会更大。因为这个原因，例行的天花疫苗接种在二十世纪六十年代末就被淘汰了。
Active and passive immunity
If you are exposed to an organism, either during your day-to-day life or through vaccination, you will eventually develop an active acquired immunity to that organism. Your body will produce its own antibodies, and, in most cases, you will not have to worry about subsequent exposures to the disease.
无论是日常生活还是通过接种疫苗，如果被微生物感染，你最后都会对那种微生物产生有效的后天免疫。你的身体会产生自身抗体，并且在许多情况下，将不用担心被这种病原微生物再度感染。
In some cases, however, the risks of contracting a disease are so severe that you may not be able to wait the days or weeks that are necessary for your own body to produce antibodies. Also, in the situation where a person’s resistance is terribly weakened as a result of cancer chemotherapy or for other reasons, the body may be unable to produce its own antibodies. When either of these situations occurs and a victim is in need of immediate aid, antibodies formed in another person or animal are often given. Termed passive immunity, this type of immunity is often short-lived but provides the necessary boost for a person to get through a potentially critical period. Antibodies utilized for passive immunity are taken from gamma globulins, proteins synthesized from a donor's blood. A mother also confers passive immunity on her newborn baby through breast-feeding.
然而，在某些情况下，感染上一种疾病的危险是巨大的，以至于你没有足够的时间等待身体产生抗体。还有在癌症化疗期间或其他原因，机体的抵抗力会被严重削弱，身体可能无法产生抗体。在上述两种情况中的任何一种情况下，一个急需救治的病人可以从另一个人或者动物体内取得现成的抗原。获得性免疫，这种类型的免疫存在时间通常很短，但却能促使机体经受一段潜在的危险期。后天免疫的抗体是由供血者血液中的免疫球蛋白合成的。一个母亲也可以通过哺乳给予新生儿后天免疫。
Unit 4
Common Diseasese and Ailments
There is no end in sight in the battle between human beings and the diseases that can destroy them. However, in the past few decades, the nature of the enemy has changed dramatically.
人类与摧毁他们的疾病之间的战斗看来将永无休止的进行下去。然而，在过去的几十年里，自然界的敌人已经发生了戏剧性的改变。
In countries where modern medical facilities are available, infectious diseases that were once widespread killers can now be prevented or diagnosed early and cured.
在一些现代医疗设施齐备的国家，过去一度是大规模的杀手的传染性疾病现在已经可以被预防或者被很早地诊断出来并治愈。
Thanks to vaccines, antibiotics, and improved sanitation, most of the dreaded epidemics of the past are not likely to recur.
多亏了疫苗，抗生素，还有公共卫生条件的改善，过去绝大部分令人可怕的传染病已经不大可能会卷土重来了。
Today's major killers are noninfectious diseases-especially the various forms of cardiovascular disease and cancer. As life expectancy increases, people are more likely to succumb to degenerative conditions that the aging body is susceptible to.
今天人类主要的杀手是那些没有传染性的疾病---------尤其是指各种各样类型的的心血管疾病和癌症。随着预期寿命的延长，人们更可能死于易侵袭年老躯体的退化性疾病。
In addition, many factors of modern life - such as environmental pollution, occupational hazards, stress, a sedentary lifestyle, an unhealthy diet, the use of cigarettes, drugs and alcohol abuse - contribute to the development of disease.
另外，现代生活的很多因素--------例如环境的污染，职业性的危险，压力，久坐不动的生活方式，不健康的饮食，吸烟，滥用毒品和过度饮酒--------都导致了患病。
One of the most common serious afflictions in modern society is heart disease. This general label encompasses many different abnormal conditions, including congenital heart defects(many of which can be repaired surgically), diseases of the pericardium (the tissue surrounding the heart muscle), and diseases affecting the heart muscle itself (the myocardium).
在现代社会一种最常见的严重的疾病之一便是心脏病，这（心脏病）总的来说包括许多不同的异常情况，包括先天性心脏缺损（其中有很多病例可以通过外科手术修复），与心包有关的疾病（心包是环绕在心肌周围的组织），和影响心脏肌肉本身的疾病（心肌）。
Physicians can often detect or predict heart problems by measuring the rate of the heartbeat (called the pulse) and by taking the patient's blood pressure.
医生经常可以通过测量心脏搏动的速率（又叫脉搏）和通过测量病人的血压检测或者预测心脏问题。
Another important diagnostic tool is the electrocardiogram (EKG), a record of the electrical activity of the heart, which can reveal abnormal cardiac rhythm and myocardial damage.
另一个重要的有诊断价值的工具是心电图，一个心脏（生物）电活动的
记录
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，这可以揭示出异常的心律和心肌损伤的问题
When heart disease is suspected and more detailed information is needed, an angiogram is ordered. This series of X-ray films (taken after the injection of a radiopaque substance) defines the size and shape of various veins and arteries.
当怀疑是心脏病和需要更多详细信息的时候， 就要求拍血管造影照片。这一系列的X光片（在注射了不透射线的物质后得到的）能够显示不同静脉和动脉的大小与形状。
The most common cardiovascular disease is atherosclerosis (hardening of the arteries). Atherosclerosis of the coronary arteries may cause the development of a coronary thrombus (blood clot), which blocks the flow of blood to the heart muscle.
最常见的心血管疾病是动脉粥样硬化（动脉硬化）。 冠状动脉的粥样硬化可能会导致患上冠状动脉血栓（血凝块），这会阻碍血液流向心脏肌肉。
If, as a result, part of the heart muscle dies, the condition is called myocardial infarction (a heart attack).
如果造成一部分心肌坏死，这种情况被称为心肌梗塞。
Some symptoms and signs of a heart attack are pain in the chest (and sometimes also in the jaws and arms), shortness of breath, irregular pulse, nausea, and perspiration. Prompt cardiopulmonary resuscitation can save victims from sudden death.
心肌梗塞的症状和迹象是胸部的疼痛（有时候这种疼痛也发生在颌骨和手臂），呼吸急促，不规则的脉搏，有恶心感，和出汗。迅速的心肺复苏术能够将受害者从猝死中救回来。
when atherosclerosis affects the carotid and vertebral arteries (which supply blood to the brain), a stroke may result,causing paralysis (paralytic stroke)and sometimes affecting speech and brain function.
当动脉粥样硬化影响颈动脉和椎动脉（就是它们向大脑供应血液的）时，中风可能就会发生，导致麻痹（瘫痪中风）以及有时候影响发言和大脑的功能。
Atherosclerosis can also weaken the aorta wall,causing it to develop a ballonlike structure called an aneurysm. large aneurysms can rupture, causing fatal hemorrhage.
动脉粥样硬化也会使主动脉壁变薄 ，导致它形成一个气球状的结构叫做动脉瘤。大的动脉瘤会破裂，导致致命的出血。
Patients can decrease the likelihood of developing atherosclerosis by cutting down on their consumption of fats,cutting out cigarettes,and getting adequate exercise.
病人可以通过减少脂肪的 摄入，停止吸烟，和进行适当的运动来降低动脉粥样硬化发生的可能性。
Less serious but still frightening is the condition called angina pectoris, chest pains that occur when the heart muscle does not get enough oxygen (often because of a temporary spasm of a vessel).An attack is usually caused by overexertion and can be relieved by rest and nitroglycerin tablets.
虽然没有那么严重但是仍然令人感到可怕的是一种病情叫做心绞痛，在心肌没有得到足够的氧气的时候发生胸痛（通常是因为血管暂时的痉挛）。心绞痛发作通常是由过度用力引起的，可以通过休息和使用硝酸甘油片来减轻。
The relationship between cardiovascular disease and hypertension (high blood pressure) is well known,so patients with high blood pressure are generally placed on a regimen including a low-salt diet,regular exercise,and sometimes medication that will bring blood pressure down to within normal limits.
心血管疾病和高血压（高的血压）之间的关系是众所周知的，所以高血压病人通常采用一个养生法疗养，（这种养生法）包括低盐的饮食、规律的运动，有时还需服用使血压下降到正常的界线内的药
Another major killer is cancer. Cancer is characterized by an unrestricted growth of abnormal cells.
另外一种主要的杀手是癌症。癌症以异化细胞无节制地增长为特征。
There are three main types of cancer:a carcinoma originates from the surface cells of the skin or the linings of the internal organs;a sarcoma attacks the muscles,bones,tendons,cartilage,fat,blood vessels,lymph system,or connective tissue;
主要有三种类型的癌症(恶性肿瘤)：肿瘤癌起源于皮肤表面的细胞或者是内部器官的内层细胞。肉瘤攻击肌肉，骨头，肌腱，软骨，脂肪，血管，淋巴系统和结缔组织。
leukemias afflict the blood-forming cells.Some cancers grow slowly;other spread rapidly,doubling in bulk in days.
白血病破坏了造血细胞。另一些癌症增长得比较缓慢， 另外一些扩散得比较快，在几天后，癌症部位的体积就加厚。
Cancer can appear anywhere in the body,but some common sites are the lungs,breasts,uterus skin ,colon,prostate,and blood.
癌症可以在身体的任何一个部位发生，但是一些见的场所是肺，胸部，子宫，皮肤，结肠，前列腺和血管。
Symptoms vary greatly depending upon the location,but some of the most common symptoms are unusual bleeding or discharge,a thickening in any area, a sore that does not heal,hoarseness or difficulty swallowing,indigestion,a change in bowel or bladder habits,or unexplained weight loss.
不同位置有不同的症状，但是一些最常见的症状就是异常的出血或分泌物，某些区域增厚，久治不愈的溃疡，喉咙沙哑和吞咽困难，消化不良，大小便习惯改变和不明原因的消瘦。
A disease that attacks the kidneys is nephritis. There are many different types and many causes of nephritis,including bacteria and toxins.
攻击肾脏的疾病叫做肾炎。肾炎有很多种不同的类型，造成肾炎的原因也有很多种，包括了细菌感染和毒素侵害。
The kidneys regulate the elimination of urine from the body.If the disease becomes severe enough to destroy the kidneys,the victim can be saved through the transplantation of a donor's kidney or by regular use of a renal hemodialysis machine.
肾脏调节从身体里排出来的尿液。如果这个疾病变得非常的严重伤害到肾脏，患者可以通过捐献者的肾的移植或者定期通过肾脏的血液透析机器被救治。
This machine substitutes for the kidneys,cleansing the body of its liquid wastes.
这个机器代替肾脏，清除身体的废液。
Diabetes mellitus is a disease in which the body no longer uses sugar properly.
糖尿病是一种使身体不能再正常利用糖的疾病。
In a healthy body,special cells in the pancreas secrete the hormones insulin and glucogan,which help to store sugar.In the body of diabetic,these hormones are inadequately produced or utilized.
在健康身体状态下，胰腺里的特殊的细胞分泌胰岛素和胰高血糖素，这些激素有助于储备糖。在糖尿病患者身体里，这些激素产生不足或者是被利用得不充分。
The disease is often diagnosed by the discovery of sugar in the urine and abnormally high levels of sugar in the blood.
糖尿病通常是通过发现尿液中含糖和血液中有反常的高浓度水平的糖而被诊断。
If the disease is not controlled,serious complications can develop affecting the eyes,kidneys,and the circulatory system.
如果糖尿病得不到控制，会患上影响眼睛，肾脏和循环系统的严重的并发症。
Arthritis and rheumatism are general names for approximately 100 diseases that produce inflammation or degeneration of connective tissue.
关节炎和风湿病是一百多种产生炎症和结缔组织退化的疾病的概称。
Some of these diseases are infectious and primarily affect younger people. Rheumatic fever, for example, is a bacterial infection that occurs mostly in children or teenagers.
这些疾病中的一些是有传染性的，而且主要感染年轻的人群。例如，风湿性的发热是一种发生在大多数小孩和年轻人身上的细菌性感染疾病。
Rheumatoid arthritis predominantly strikes women between 20 and 60. However, the most common rheumatic disease is a noninfectious, noninflammatory degenerative joint disease--osteoarthritis.风湿病的关节炎主要出现在20岁到60岁的妇女身上。然而最常见的风湿性的疾病是一种没有感染性、没有炎症性退化的关节性疾病，叫做骨关节炎 。
To some degree, it affects nearly all older adults, causing swelling, pain, and stiffness in joints.在一定程度上，骨关节炎几乎侵袭所有的老年人，造成他们关节肿涨、疼痛和僵硬。
Beside osteoarthritis ,many other noninfectious diseases can limit the activities of the elderly.
除了骨关节炎,许多其他非感染性疾病会限制老年人的活动。
Osteoporosis(a condition in which bone loss exceeds bone replacement so that the bones become less dense,more porous ,and more brittle)often leads to fractures,especially of the hip bone.
骨质疏松症(一种因骨质流失超过骨质新生,以至于骨小梁变得稀疏、更多孔、和更脆的疾病)常常会导致骨折,尤其是髋骨。
Many conditions conspire to decrease the sensory perception of the elderly.
多种疾病的共同作用，使老年人的感官能力下降。
Cataracts (created when the lens of the eyes-or a portion of it-becomes opaque and sometimes swells or shrinks) interfere with vision.
白内障(造成眼睛的晶状体或部分晶状体变得不透明,并且有时膨胀或收缩)，会影响视力。
Deterioration of nerves in the inner ear causes the characteristic old-age hearing loss.The senses of taste and smell also deteriorate in old age.
内耳神经的退化造成典型的老年人听力退化。味觉和嗅觉的感官也在晚年退化。
But what many elderly people fear most is the loss of mental abilities.
但是许多老人最害怕的是心智能力的衰退。
Confusion,memory loss,and inability to distinguish reality and fantasy (dementia) are all symptoms that can be caused by damage to the brain.
困惑，,记忆丧失,分不清真实和幻想(痴呆) ，所有的这些症状，都可能是由大脑损伤造成的。
They may result from external injury,a stroke,or deterioration of the brain cells due to inadequate blood and oxygen supply.
他们可能由外部损伤、中风,或血液和氧气供应不足造成的大脑细胞恶化等原因引起的。
One common cause of severe mental deterioration is Alzheimer's disease,a neurological brain disorder in which there are a variety of abnormal chemical changes in the brain and characteristic nerve cell "tangles".
一种常见的病因导致严重精神恶化的是阿尔茨海默氏病, 一种神经学上的大脑紊乱，其中存在各种各样的异常的大脑化学物质变化和独特的神经细胞“紊乱”。
Among contagious diseases,many of the major killers of the past are no longer widespread problems.
在传染病当中，过去的许多主要传染病杀手已经不再是威胁了。
Smallpox,for example,has been eradicated in most parts of the world by vigorous immunization campaigns.
例如，天花已经在世界上大多数地区的通过积极免疫接种根除了。
Tuberculosis,a bacterial infection which commonly affects the lungs,was the numberone killer of Americans prior to1909.
肺结核，一种由细菌感染，通常感染肺部的病，在1909年之前是美国的头号杀手。
Today,to test for TB,a simple skin test is widely given periodically as part of a routine medical checkup .
今天，为了检查有无肺结核， 会在常规的体检中定期广泛地进行一个简单的皮肤测试。
If the results are positive,a chest X-ray is taken to determine whether the disease is dormant or active.
如果结果是阳性的，则要用胸部X光检查来定性此疾病是处于潜伏期还是病变期。
In either case,the condition can then be controlled or cured by medication.Another infection of the lungs,pneumonia,is also much less dangerous than it once was,thanks to antibiotics.
这两种情况都可以通过药物进行控制或治疗。另一种肺部感染——肺炎，多亏了抗生素，使它的危险也比以前减少许多。
Many diseases are transmitted(传播；发射) by sexual contact . Commonly called sexually transmitted diseases(性传播疾病) (STD) , these include gonorrhea(淋病), syphilis(梅毒), genital herpes(生殖器疱疹),and others .
许多疾病由性接触传染。这些疾病通常被称之为性传播疾病，包括淋病，梅毒，生殖器疱疹等等。
Some of this can be very destructive to the body if not treaded, but all can be either cured or controlled by medication.
这些疾病中，有的疾病若不进行治疗会对身体产生很大的伤害，但它们都能用药物治愈或控制。
By far the most frightening of the sexually transmitted disease is Acquired Immune Deficiency(缺乏，不足) Syndrome (AIDS).
到目前为止，这些性传播疾病中最吓人的就是获得性免疫缺陷综合征（艾滋病）。
This fatal disease is spread by direct sexual contact or exchange of blood ( for example , by use of contaminated (使污染)hypodermic(皮下的) needle).
这个致命的疾病由直接的性接触或血液的交换（例如，使用受污染的皮下注射针）传染。
AIDS destroys its victim’s immune system, leaving the patient unprotected against infections that healthy people could fight off.
艾滋病破坏患者的免疫系统，让患者在感染时处于无保护的状态而不能像正常人一样抵抗感染。
“An ounce of prevention is worth a pound of cure” is an expression that especially to AIDS, not only because the use of condoms and sterile needles can protect from the disease, but also because at present there is no cure.
“医小病治未病”（小防胜于大治）这是对艾滋病最贴切的表达，不仅因为使用避孕套以及无菌的注射器就能防止感染，更因为此病目前无药可医。
At the other end of the disease spectrum(谱系；整个范围) are many conditions that may make people feel temporarily “ under the weather ” but are not serious enough to require a physician’s care -especially if they are only occasional and short-lived .
在疾病范畴的另一端，有很多或许会让人暂时“身体不适”但又并非严重到要去看医生的情况，尤其是那些仅是偶然发生且持续时间短暂的症状。
Common infectious conditions such as a cold , the flu , or diarrhea(腹泻) (loose bowel movements) are often self-limiting and can be treated symptomatically(症状方面) with over-the-counter drugs .
普通的传染病例如感冒，流感或腹泻（疏松性肠内部运动）通常有其自限性并且能够使用非处方药对症治疗。
People often endure the acne(痤疮) of adolescence and the hemorrhoids(痔疮) of pregnancy without consulting a physician , especially when the condition are not severe .
人们经常忍耐着青少年型的痤疮还有怀孕引起的痔疮而不向医生咨询，特别是当情况并不严重的时候。
Minor traumas（创伤） are often self-treated with routine first aid .
较小的创伤通常以常规的急救护理进行自行治疗。
Most people know that superficial(表面的，表浅的) lacerations(划破，撕裂) (cuts) should be thoroughly cleaned and bandaged and that immediate immersion(浸入) in cold water will relieve the pain of a slightly burned finger or a sprained(扭伤) ankle .
大多数人都懂得皮外伤应该被彻底地清洗以及包扎，还有将轻微烫伤的手指头或扭伤的脚踝立即浸入冷水中可以缓解疼痛。
The study of disease should not make students feel fragile and vulnerable .
对疾病的学习不应让学生们感到人体是脆弱的和容易受到攻击的。
It is important to remember that the human body has a remarkable ability to protect itself against disease and to cure itself when illness or injury dose occur .
重要的是要记住，人体具有卓越的保护自我免受疾病侵害，以及在疾病或创伤发生时自我治愈的能力。
Moreover, when serious illness strikes, modern medicine has extremely sophisticated tools for fighting back.
此外，当严重的疾病攻击人体时，现代医疗也拥有极其精致的工具来击退它们。
Unit 5
How does air get from the outside all the way to the alveoli --- a distance of perhaps 50 centimeters?
空气是怎样从外界获得并一直运送至肺泡 -- 一个与外界相隔大概50cm的距离
Of course, an oxygen molecule might traverse the entire distance by virtue of its own molecular movement, but the diffusion of an appreciable number of molecules is a slow process.
当然，氧气的分子也可能依靠自己的活动而通过整个距离，但相当数目的分子的扩散则是一个很慢的过程。
As everyone knows, the movements of the chest have something to do with breathing .Simple observations show that when the chest increase in diameter, air moves into the body
众所皆知，胸部的活动与呼吸有关。简单的观察显示：当胸廓直径增大，空气就进入体内；
When the chest decreases in diameter, air is expelled from the body .We might guess that the expansion of the lungs causes the chest to expand .However, the cause-and -effect relationship is precisely the opposite.
当胸廓直径减少，空气就从体内排出。我们可以猜测肺部膨胀会导致胸部扩张。然而，这种因果关系恰恰是相反的。
A lung is incapable of expanding actively ; in other words ,there are no muscles in the lung that can cause it to expand .Functionally ,the lung is but （only）an elastic bag; Although it is living and complicated, in some ways it is not too different from a rubber balloon.
肺不能积极主动地扩张，也就是说，肺没有肌肉可使其扩张。从功能上来说，肺就只是一个有弹性的袋子。尽管他是复杂而富有生命力的，但从某些方面来说，它和橡皮球没什么太大差别。
Once expanded, it can contract again because of its elasticity, but it cannot expand itself any more than a rubber balloon can expand itself.
一旦扩张，肺能因弹性而重新收缩；但就像橡皮气球一样它不能自我扩张。
Stripped of all details of structure, the lungs are an elastic bag completely surrounded by the chest walls and diaphragm, except for the single opening, the trachea, leading to the outside.
除去所有结构上的细节，肺是一个有弹性的气袋，除了一个通往外界的开口（气管）外，完全被胸腔壁和横隔所包围。
Because the lungs are open to the outside, the pressure of gases in the lung cavity is at all times the same as the air pressure outside.
因为肺与外界相通，肺腔内的气体压总是与外界大气压一样。
Should anything tend to increase the pressure in the lung cavity ,gas will go out through the trachea until equality of the pressures is achieved .Anything tending to decrease the gas pressure within the lung cavity will bring about an intake of gas.
如果肺腔内的压力增加，气体就会通过气管流出，直至压力达到平衡；如果肺腔内的气体压降低时，则外界气体就会进入。
We take air into the lungs as follows: The diaphragm moves downward, and the chest walls move outward .The elastic lungs follow suit, thus increasing the volume of the lung cavity.
我们将空气带入肺的过程如下：隔膜向下移动，胸膜向外移动。有弹性的肺效仿膈膜和胸膜的运动，这就使得肺腔体积增加。
This increase in volume tends to decrease the pressure, but the opening of the trachea permits more air to enter instead .Thus the process of inspiration takes place.
尽管体积增加致使压强减小，但更多的空气会通过气管进入肺腔内。这样吸气的过程就发生了。
The expelling of air, expiration, is brought about by an upward movement of the diaphragm and an inward movement of the chest walls.
空气的排出呼气，它是由隔膜向上移动，以及胸膜向内移动引起的。
Now ,let us examine the machinery that brings these changes in volume of the chest cavity .The ribs, hinged to the backbone, are moved forward and upward by muscular action .The diaphragm is itself a muscle attached to a central tendon;
现在，让我们来检测下引起那些胸腔容积变化的机构。与脊柱相连接的肋骨因肌肉的作用向前方和上方运动。隔膜是自身的一束肌肉连接到中央腱；
When the strands of diaphragmatic muscle contract, the whole diaphragm becomes taut and moves downward, thus pushing the contents of the abdominal (belly) cavity downward and outward. As a result, there is an increase in the volume of the chest cavity and a protrusion of the belly.
当这股膈肌收缩，整个隔膜就会变得紧张并向下移动，从而推动腹腔内容物向下和向外移动。结果，这里会导致胸腔容积增大以及腹部前突。
Breathing may be carried out principally by the muscles of the thorax(chest) ,in which case it is called thoracic breathing ,or principally by the diaphragm ,in which case it is called abdominal breathing .
呼吸可能主要由胸肌实现的，这种情况叫做胸式呼吸；或者主要由膈肌实现的，这情况叫做腹式呼吸。
Usually both types of breathing are employed. There are considerable individual differences in the types of breathing .At one time, it was thought there was a difference in the two sexes in this regard - and, in truth, there was.
通常两种类型的呼吸都会被使用，并且呼吸类型有着相当大的个体差异。人们一度认为，男女在这方面有区别。事实上，并非如此。
Studies made around 1900 showed that most women were thoracic breathers, whereas many men were abdominal breathers .This difference was regarded by some as an inherent secondary sexual characteristic, like a beard or a deep voice.
大约在1900年的研究显示，大多数女性是胸式呼吸者，相反许多男性是腹式呼吸者。这个差异被一些人认为是一种固有的第二性征，就像胡须和低沉的声音一样。
It was reasonable enough assumption, perhaps, but when similar made around 1925 failed to reveal any difference between the breathing of men and women, it was realized that the predominance of thoracic breathing among women observed earlier had been caused by the formidable corset they used to wear.
或许这是足够合理的设想，但是大约在1925年做的相似的研究却未能显示在男性和女性呼吸之间有任何差异，人们意识到，先前在女性中观察到的胸式呼吸占主导位置的情况，是由她们过去穿的令人生畏的紧身胸衣所导致的。
An error of interpretation of this sort makes the experimental scientist cautions about giving biological significance to a sex difference when the observation is made in only one society at one period.
这一类解释上的错误使实验者在解读特定社会、特定时期两性区别的生物学意义时变得谨慎小心。
Folkways and customs can also corset or harness the minds of men and women, and thus cause striking differences between the adult sexes.
民俗和习惯也能够禁锢或束缚男性和女性的思维，这就导致了成人性别有着显著差异。
These remarks are not made to deny the existence of biological differences but only to encourage caution in interpreting observations.
说这些话的用意，不在否认两性生物学差异的存在，而只是为了提倡对观察结果进行解读时多加小心。
Every analytical procedure leads in some way to an abnormal separation of things that are normally together.
从某种程度上来说，每一种
分析
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性的程序总会会导致一些原本相关的事物却异常地分开。
Having analyzed the body into anatomical system, we run into occasional difficulties when studying functions, for even a single function usually-perhaps always –involves the co action(共同作用） of several systems. So it is with breathing.
把人体分成解剖学系统后，当我们在研究功能时，偶尔会遇到困难；因为即使是单一的功能通常也会（也许总是）涉及几个系统的共同作用。呼吸就是如此。
If we ask how breathing is controlled, we find that we must consider the actions not only of the breathing system but also of the circulatory and the nervous system.
如果我们问如何控制呼吸？我们发现这除了要考虑（与）呼吸系统（有关）之外，还要考虑循环系统和神经系统。
We can discuss the control of breathing here by appealing only to commonly known facts :(1)the circulatory system circulates the blood throughout all parts of the body; and (2)the nervous system transmits “messages”(stimuli) from the brain to the various parts of the body by nerves.
这里，我们可以仅借助于人们所共知的事实来讨论呼吸的控制。（1）循环系统使血液循环流经人体各个部分；（2）神经系统通过神经从大脑向人体各个部分传达信息（刺激）。
A man can deliberately stop breathing for only a short period of time. After a minute or so, no matter how strong his will power，he starts to breathe again.
人可以故意地不进行呼吸，但这只能维持很短的时间。大约一分钟后，无论他的意志力如何强的，他又会重新开始呼吸。
What is it that makes him breathe? A little thought about what must go on during suspended(暂停的） breathing will suggest answers. Respiration goes on all the time.
是什么使得他呼吸？ 稍微思考一下在摒住呼吸期间必然发生的事，就能想起这方面的答案。
If breathing is stopped —that is, if exchange of gases between the body and the outside world is stopped- inside the body the concentration （浓度）of carbon dioxide will increase and that of oxygen will decrease.
如果停止呼吸——那就是说，假如人体和外界之间停止气体交换——体内二氧化碳的浓度将会上升，而氧气的浓度将会下降。
Will either of these changes cause breathing to resume?
这其中一种发生改变也将造成呼吸重新开始吗？
Simple experiments with a man (or other mammal哺乳动物) who is breathing freely reveal that either low oxygen or high carbon dioxide concentration in the inspired air can cause an increase in the rate of breathing, but that high carbon dioxide concentration is by far the more effective .
用可以自由呼吸的人类(或其它哺乳动物）做的简单实验显示，吸入空气中的氧浓度偏低或二氧化碳浓度偏高都能引起呼吸速率的加快，但高二氧化碳浓度的效果远为明显。
How does carbon dioxide exert发挥 its effect? Anatomical observation reveals nerves going from a part of the brain called the medulla髓质 to the thoracic muscle 胸肌that take part in breathing (the diaphragm隔膜 and the muscles between the ribs).
二氧化碳是怎样发挥它的作用？解剖观察揭露表明：来自大脑的一部分神经纤维被称为髓质，而从髓质到胸肌的神经则参与了呼吸（在肋骨之间的肌肉和隔膜）。
Varying the concentration of carbon -dioxide in the blood circulating through the medulla affects the rate of breathing: when CO2concentration is high, breathing is rapid;
改变流经延髓的血液中的二氧化碳的浓度会影响呼吸的速率：当血液中二氧化碳的浓度高时，呼吸加快，
when CO₂is low the rate of breathing slows or stops. The medulla, therefore, is spoken of as the breathing center of the body.
当二氧化碳的浓度低时，呼吸变慢甚至停止。因此，髓质被认为是人体的呼吸
中枢。
Without the evidence of the experiments we would probably guess that lack of oxygen is the more important stimulus. After all, it is oxygen that we need. Carbon dioxide is a waste product; yet the mechanism机制 is tied to it.
如果没有这些实验证据，我们可能猜测，缺氧是更为重要的刺激物。毕竟，氧气才是我们所必需的。CO2是一种废气；然而这个（呼吸）机制却与CO2紧密相关。
This observation broadens our conception of “waste products.” Even if a substance物质 is waste material, produced in excess and requiring to be disposed of, it still may perform important functions.
这个发现拓宽了我们对“废物”的概念。即便一种物质是废物，生产过量而需要处理掉，它仍然可能有着重要的功能。
In designing automatic control equipment, engineers often include a “manual override,”which allows a human operator to bypass绕过 automatic devices and control the equipment himself.
在设计自动控制设备时, 工程师们常常会加入一个“手动管控制器”，它使操作者能绕过自动控制装置，自己来控制设备。
The breathing control mechanism of the body offers a similar option. A person can shut off his own automatic control system and breathe at the rate and depth that he wishes –but only for a while and within certain limits.
身体的呼吸调节机制提供了一个类似的选择。一个人可以关闭自己的自主控制系统，随心所欲地调节自己的呼吸率和呼吸深度，但这只能是暂时的且是有一定的限制性的。
If he choose to stop breathing altogether he can do so only until the CO₂ concentration in his blood reaches a critical level, when the automatic system takes over no matter how strong his will power.
如果他想完全停止呼吸，这只有在血中CO2浓度尚未达到临界程度之前才能做到。无论人的意志如何强大，一旦达到这一程度，（这时）自动系统就会接而管之。
A small child indulging in a temper tantrum发怒 may hold his breath until he gets very red in the face. A naive mother may fear that he will kill himself; but he will not, because he cannot.
一个放纵自己发脾气的小孩，可能会憋气直到自己满脸通红。一个稚气的母亲可能会担心他会因此自杀，但是他不会，因为他做不到。
The human mother can safely trust Mother Nature to put a stop to the threat.
人类母亲可以安全地信任大自然母亲会制止这种威胁。
Unit6
The Kidney and Its Working Unit
For many diners，eating tender，pale green shoots of asparagus is a pleasurable spring time event, but the gastronomic experience has a peculiar sequel ：the next time they urinate, even if just 20 minutes after eating, they notice the characteristic scent of asparagus.
对于一些进餐者来说，进食一些嫩的、浅绿色的芦笋幼苗是一种愉快的春季活动，但是美食学的经验有着一种独特的后续：下一次他们小便，甚至是进食20分钟后，他们会注意到小便中会含有一种独特的芦荟的香味。
A chemical in the food crosses the gut, enters the bloodstream，is filtered out by the kidneys，and appears in the urine with amazing speed. Actually, the chemical is acted on no faster than any other compound.
芦荟化学物质穿过小肠，进入到血流，在肾脏中被过滤掉，以惊人的速度出现在小便中。事实上，对于这一化学物的作用并不比其他化学物快。
The kidneys are simply marvels at processing body fluids and filtering out the urea; the sodium，potassium，or chloride ions ； and the glucose, water, and other materials that need to be excreted.
起到加速体液循循环并过滤出尿素,钠、钾、氯离子，葡萄糖，水及一切需排泄的东西作用就是肾脏。
The key to a kidney’s rapid functioning lies in its complicated internal structure and in the efficient plumbing system of which it is a part.
肾能快速运作的一个重要因素是其内部复杂的结构和组成其一部分有效的管道设施。
The Kidneys and Other Organs of 1he Excretory System
It is sometimes stated that urination is our most compelling bodily function. You will probably agree if you have ever been hungry，tired, cold, and had a full bladder simultaneously and can recall the order in which you addressed those needs.
人们有时说排尿是我们身体最急迫的功能。如果你曾经有过饥饿、疲倦、寒冷及膀胱满胀等感觉并能回忆起你处理这些身体需要的顺序，你就会同意以上那种说法。
This urgency has to do with the necessary waste removal role of the excretory system and with the system’s particular anatomy.
这种紧迫感与排泄系统重要的排泄以及特殊的解剖系统有关。
The main organs of the excretory system are the two plump，dark red，crescent-shaped kidneys， each about the size of an adult’s fist and located high in the abdominal cavity behind the stomach and liver
泌尿系统最主要的器官是两个红黑色的，鼓起的呈新月状的肾脏，每一个的大小都相当于一个成年人的拳头，它们位于腹腔上面、胃和肝脏的后面。
For each kidney to carry out its vital blood-filtering activities, it must receive a large,steady flow of blood. This it does through the renal arteries, twin branches directly off the body’s main blood vessel, or aorta..
因为肾脏执行过滤血液的重要功能，它必须接收一股强大持续的血流。肾脏通过肾动脉获得血液，肾动脉是直接来回人体最重要的血管动脉或者主动脉的一对分支。
Cleansed blood then leaves each kidney in a large renal vein that drains into the body’s largest vein.
过滤后的血液经粗大的肾静脉离开肾脏，流入机体的最大静脉
As the kidneys filter and remove excess water and waste substances from the blood，these materials collect as a concentrated urine in a central cavity in each kidney，then flow down a long tube called a ureter. The two ureters dump urine into a single storage sac，the urinary bladder, which in an adult can hold about 500ml (a pint) of fluid.
肾脏将血液过滤，除去血液中多余的水分和废物时,废物在肾脏中部空腔里集合起来形成尿液,尔后流入输尿管。两条输尿管将尿液输入一个单一的储存囊,即泌尿的膀胱。成人的膀胱大约可容纳500 ml。
The kidney has three distinct visible zones ： an outer renal cortex zone，where initial blood filtering takes place ； a central zone ( renal medulla)，divided into a number of fan-shaped pyramid regions that help conserve water and valuable solutes ； and a hollow inner compartment ( renal pelvis)，where urine collects before it passes out of the kidney and down the ureter.
肾脏有三个明显的有区别的区域；一个外层的肾皮质区：血液过滤最开始发生的地方；一个中间区（肾髓质），分成许多可以帮助保存水分和其它溶质的扇形的成金字塔的区；和一个内层的中空区（肾盂），是尿液在排出肾脏和流入输尿管之前收集起来的地方。
The functional units of the kidney, twisted tubules called nephron，reach from the outer cortex down into the central zone and drain into the hollow center.
肾脏的功能单位，是一些扭曲的管道，叫做肾单位，它从外皮质到中间区然后进入到中心的中空区
.Have you ever cleaned out a desk drawer ——sorting, saving certain items
for future use, discarding others, and then rechecking the drawer one last
time? 你曾经清理过抽屉吗？--挑选、保留一些东西以备后用，清除其他的东西，然后再一次检查。
If so, you have approximated the kidney’s general sorting and cleansing
action and its three basic processes ——filtration，reabsorption， and secretion —
all of which involve the nephron.
有这样的经历,你就会大致了解肾脏的挑选和清理作用以及肾单位参与的过滤,重吸收，分泌--三个过程。
A human kidney contains roughly 1 million nephrons，each one a long，twisted，looping tubule. The tubulehas one end that is enlarged and cup-shaped like a punched basketball and that
lies in close contact with blood capillaries ； the other end drains away urine. If all the nephrons in an adult’skidney were straightened out and placed end to end, they would from a
microscopically slender tube about 80km (50 miles) long.
人类的一个肾大约有一百万个肾单位,肾单位为长形、扭曲、环状的细管。肾单位的一端扩展而杯状，如同一个被刺破的篮球，与毛细血管紧密相连;另一端进人输尿管。如果将成人肾脏所有的肾单位全部拉直并一端接一端地连在一起，可形成微观的长约80 km(50英里）的纤微导管。
Nephrons are amazingly efficient at selectively removing wastes form the
blood circulation while simultaneously conserving water, mineral ions, glucose,
and other needed materials. In an adult human, 180 liters or more of blood —
enough to fill a bathtub — pass through the 2 million nephrons in the two
kidneys each day.
肾单位在选择性清除废物的同时又保留水分，矿物离子,糖及其他有用物质上有惊人的作用。一个成年人，每于穿过两个肾脏2百万个肾单位的血液有180 L或更多，足够装满一个浴盆。
We do not, of course, urinate 180 liters a day or even the 6 or 7 liters of fluid our bodies contain, but instead the much more reasonable amount of about 1. 5 liters per day. Clearly, the nephrons must accomplish a great deal of water recycling and conservation before they produce that smaller quantity of urine. Let us now take a close look at how a nephron works.当然,我们并非每天都排出180 L或6 ~7L体液,而是一个比较合理的数量一一每天约1.5升。显而易见，肾单位必须完成大量的水分再循环和保存工作才能产生出相对小量的尿液。现在我们来仔细看一看肾单位是如何工作的。
The nephron ’s specialized shape enables it to carry out three basic processes — filtration of small molecules from the blood，reabsorption of useful molecules from the urine back into the blood， and secretion of ions and some drugs from the blood into the urine.肾单位特殊的武装使它能够执行3个程序--从血液过滤出小分子’从尿液中再吸收有用的分子并输回血液,从血液中分泌出离子和药物并将其输入尿液。
The portion of the nephron that filters water and solutes from blood is the enlarged，cuplike Bowman ’s capsule in the kidney’s outer cortex.Each Bowman ’ s capsule surrounds a tight bundle of capillaries called a glomerulus, much the way the fingers of your right hand can wrap around your left fist.肾单位中起到水和溶液过滤作用的部位是扩展的杯状的位于外肾皮质的鲍曼氏夹。每个鲍曼氏夹包裹着一捆紧密的毛细血管团（称为肾小球），就像右手的手指抱住握拳的左手的样子。
This enclosing
capsule of kidney tissue surrounding a tuft of blood capillaries forms the
closest contact between the excretory and circulatory systems. A finely meshed
filter lies between the blood and the cavity of Bowman’s capsule like a
submicroscopic colander.
肾脏中这种封闭的被膜结构加上周围的毛细血管团形成了排泄系统和循环系统间最紧密的联系。一个精细的网状过滤器位于血液和鲍曼氏夹空腔之间，如同一个亚微观的滤器一样。
As blood moves along through the capillaries，blood pressure forces the yellowish fluid portion of blood out of the capillaries, through the pores of this delicate filter, and into the Bowman’s capsule, just as water pressure forces coffee through a coffee filter.
当血液流经毛细血管时,血压将血液中的黄色液体部分压出毛细血管穿过极其细微的滤孔,进入鲍曼氏夹，就如同水压使咖啡过滤一样。
The fineness of the pores is ultimately responsible for the nephron’s blood filtration activities ： the Bowman’s capsule filter allows wastes, water, and other small molecules to seep through its minute openings，while the crucial components of blood ——red cells， antibodies, and other large proteins —remain behind in the capillaries.
孔的细微性使肾单位的血液过滤功能最终得以完成。鲍曼氏夹滤器只允许废物、水和其他小分子渗入微小的滤孔中，而血液中重要的成分——红细胞、抗体和其他大的蛋白质分子，仍保留在毛细血管中。
The passage of water, of sodium，potassium，and chloride ions，and of sugars，amino acids，and urea out of the capillaries and into the lumen of the Bowman’s capsule is passive and does not require any special output of energy other than blood pressure. The fluid, or filtrate, in the capsule is still very much like blood plasma, except that it contains no large proteins or cells.
水、钠、钾、氯基酸，尿液从毛细血管中出来进入鲍曼氏囊（肾小球囊）管是被动的，只需要血压而不需要特别的能量。液体，或者说滤液,仍和血浆十分相似,只是不含大的蛋白质分子和细胞。
As it leaves the Bowman ’ s capsule，the filtrate enters the part of the nephron’s twistedtubule nearest the capsule, known as the Proximal (near) tubule. There,reabsorption begins and returns to the circulation most of the water，thesodium and chloride ions， the sugars, and the amino acids that were just filtered out of the blood in the Bowman’s capsule.
滤液离开鲍曼氏夹，进人靠近该夹的扭曲细管（近曲细管）。在邻近细管中，发生再吸收过程。在鲍曼氏夹被滤出的大部分的水,钠和氯离子，糖类,氯基酸又重回到血液中。
These materials move out through the walls of the proximal tubule and pass back into the blood via the surrounding capillaries. Instead of being driven passively by blood pressure, reabsorption of solutes in the proximal tubule depends on energy 一 costly active transport across cellmembranes.
在邻近细管中的溶液重吸收不再是受血压作用被动地发生,这种穿透细胞膜的运送是需要消耗能量的。
As the ions are being reabsorbed in this way, 80 to 85 percent of the water in the original filtrate follows them passively back into the capillaries via the process of osmosis.
当离子以这种途被再吸收的时候，原滤液中80% ~85%的水分跟随离子通过渗透作用被动地回到毛细血管。
Next，the filtrate passes down the descending arm of the nephron ’ s U-shaped loop of Henle’ s, which is bathed by an increasingly salty fluid. Water leaves the loop of Henle’s by osmosis and reenters the blood of the capillaries surrounding the tubule.
然后，滤液流人肾单位U形汉勒氏管降支,这个部位不断受到越来越多盐液的冲洗。永因渗透作用离开汉勒氏管再进入细管周围的毛细血管血液中。
The filtrate then rounds the bend in the loop of Henle’s and moves up the ascending arm and through the distal tubule ( far from the Bowman’s capsule) toward the collecting duct. The walls of the distal tubule are not permeable to water，but those of the collecting duct are;
滤液绕过汉勒氏管的弯曲沿其升支运行并经远侧细管（远离肾被膜的细管)流向收集管。远侧细管管壁不透水，而收集管管壁却透水。
and even though the filtrate passing through the duct is already quite concentrated, the surrounding tissues are even saltier. Thus, more water diffuses out of the collecting duct by osmosis and enters the blood of the surrounding capillaries.
即使通过细管的滤盐浓度巳非常高,但周围组织的盐浓度更高，因而，更多的水分通过渗透作用渗出收集管进入周围的毛细血管中。
By the time the filtrate ( now called urine) has reached the part to the collecting tubule in the innermost ( and saltiest) region of the kidney’s medulla,99 percent of the water originally filtered from the blood in the Bowman ’ s capsule has been reabsorbed and returned to the body ’ s circulation.
待滤液(现称为尿液）到肾髓质最内部(浓度最高）的收集细管时，原来经过滤的肾被膜的血液中,99%已被重吸收并返回循环系统。
While the filtration and reabsorption activities of the kidney ’ s 2 million nephrons are removing salt and urea from the blood and forming urine，another process 一 tubular secretion 一 goes on simultaneously in both the proximal and distal tubules.
当肾脏2百万个肾单位在进行过滤及重吸收除去血液中的盐分和尿素形成尿液时，另一过程--管分泌--也在近曲细管和远侧细管同时进行。
Secretion removes a number of unwanted materials — including hydrogen ions，potassium ions，environmental pollutants like pesticides,
and drugs such as penicillin and phenobarbital — from the blood in thecapillaries surrounding the nephron and secretes them into the forming
urine.
分泌作用将肾被膜周围毛细血液中一定数量的废物排入尿液,这些废物包括氢离子,钾离子，环境污染物如杀虫剂，药物如青霉素和苯巴比妥。
Tubular secretion is the physiological process that makes drug testing possible — checking a person’s urine to see if he or she has taken drugs. Drug testing employs various laboratory techniques to detect even minute traces of the metabolic breakdown products of marijuana，cocaine, and many kinds of prescription drugs.
管分泌是一个生理学的过程，它使药检成为可能--检查尿液可看出被测人是否服用过药物。药检运用了许多实验室方法,甚至可以检测到大麻、可卡因和多种处方药代谢分解产物的蛛丝马迹。
If a person takes a drug overdose and loses consciousness and no one is sure which drug was consumed, physicians quickly test the urine to identify the drug and determine the best treatment for saving the patient’s life.
如果有人服药过量失去知觉而又无人确定是哪种药物，医生可马上检验尿液来确定该药物并拿出拯救病人生命的最佳
方案
气瓶 现场处置方案 .pdf气瓶 现场处置方案 .doc见习基地管理方案.doc关于群访事件的化解方案建筑工地扬尘治理专项方案下载
。
Two additional uses — testing athletes and employees for drug use in the playing field or on the job — are currently quite controversial..
药检还有两个用途--可在赛场或工作中测定运动员或雇员是否服用过药物，不过这两种用途目前仍颇有争议。
Unit7
Stomach and Small Intestine
We humans do amazing things with food. Somewhere in the world ,one person might eat only raw whale blubber in a given day, another might eat only rice, and still another might eat only pizza and bananas, or drink dandelion wine.
我们人类对食物做了很多神奇的事情。在世界上的一些地方，那里的人在某一天可能只吃生的鲸脂，另外一些地方的人可能只吃米饭，同时仍然存在另一些人可能只吃披萨和香蕉，或是喝蒲公英酒。
Through its metabolic magic ,the human body converts these and a dizzying variety of other substances into usable energy and tissues of its own. 通过神奇的新陈代谢，人体将这些物质以及其它多种多样令人眼花缭乱的东西转化为可以利用的能量和自身的组织。
Overview of the Digestive System
A digestive system is a body cavity or tube in which food is reduced to particles, then to molecules small enough to be absorbed into the internal environment.
消化系统是一个体腔或管，在那里食物被分解成颗粒，然后被分解成小得可以被吸 入内环境的分子。
Some invertebrates have an incomplete digestive system –a saclike gut with one opening. What goes in but cannot be digested goes out the same way. Most animals have a complete digestive system.
一些无脊椎动物有一个不完备的消化系统---一个只有一个开口的囊状肠道进入。但是不能被消化的东西从原路出来。大多数动物有完整的消化系统。
This is a tube with an opening at one end for food intake and an opening at the other end for elimination of unabsorbed residues. The tube also has specialized regions for food transport, processing, and storage.
这是条有一端开口摄取食物，另一端开口排出未被消化的残渣的管。这条管也有专门的部位用于运输，加工，和储存食物。
Stretched out ,the digestive system of a human would extend 6.5 to 9 meters (21 to 30 feet). Its main regions are the mouth ,pharynx, esophagus, and gut (gastrointestinal tract).
拉伸出来，人的消化系统会达到6.5米至9米（21到30尺）。它的主要部位是口腔，咽，食管，肠（消化道）。
The gut is subdivided into a stomach, small intestine, large intestine (colon), rectum, and anus.
肠再细分为胃，小肠，大肠（结肠），直肠，肛门。
Salivary glands and a gallbladder, liver, and pancreas secrete enzymes and other substances into different parts of the system. The overall functions of the system may be summarized this way:
唾液腺和胆囊，肝脏和胰腺分泌的酶和其他物质进入系统的不同部位。系统的全部功能可以用下面的方式概括
Motility. Muscular movement of the system” tubular walls. The movement leads to the mechanical reduction, mixing, and passage of food material, then elimination of undigested and unabsorbed residues.蠕动。系统的管壁的肌肉运动。运动导致食物的机械分解，混合和通过，然后排出未消化和未吸收的残渣。
Secretion. Release of digestive enzymes, fluids, and other substances into the lumen (the space inside the digestive tube).
分泌。释放消化酶，液体，和其他物质进入官腔（消化管内部空间）
Digestion .Breakdown of food into particles ,then into nutrient molecules small enough to be absorbed.
消化。把食物破坏分解成颗粒，然后分解成小得可以被吸收的营养分子。
Absorption. Passage of digested nutrients, fluid,and ions across the tube wall and into the blood or lymph ,which will distribute them through the body.
吸收。被吸收的营养物质，液体，和离子通过管壁进入血液或淋巴，血液和淋巴把它们分配到全身。
The Stomach
The stomach ,a muscular ,stretchable sac, has three main functions .First ,it stores and mixes food .Second ,its secretions help dissolve and degrade food .Third, it helps control passage of food into the small intestine.
胃是一个肌肉发达的，有弹性的囊，主要有三个功能。首先，它储存和混合食物。其次，它的分泌物有助于溶解和降解食物。第三，它有助于控制食物进入小肠。
Stomach Acidity, Epithelium loaded with glands lines the inside of the stomach wall Each day ,cells in that lining secrete about two liters of hydrochloric acid (HCI), pepsinogens ,mucus ,and other胃酸。布满腺体的上皮位于胃壁内侧。每天，细胞在那内层分泌大约两公升盐酸，胃蛋白酶，粘液和其他物质。
The substances make up gastric fluid (that is ,the stomach ”s own fluid ) Stomach acidity increases when the HCI separates into H+ and CL- ,and this helps dissolve bits of food to form a liquid mixture called chyme.
这些物质组成了胃液（就是胃自己的液体）当HCL分解成H+和CL-时，胃酸增多，这有利于溶解小块食物形成被称为食糜的液体混合物。
The acidity kills many microorganisms present in food .It may cause heartburn when gastric fluid from the stomach backs up into the esophagus.
heartburn:心痛，胃灼烧
胃酸杀死许多存在于食物中的微生物，当胃液从胃回流到食管时，可能会导致胃灼烧。
In response to the sight ,aroma ,and taste of food ,the brain signals the secretory cells to step up activity. Also ,when food enters the stomach ,it distends the wall and activates receptors in the lining .This also leads to increased secretory activity.
大肠对食物的视觉，香味和味道做出反应，向分泌细胞发出信号以加快分泌活动。此外，当食物进入胃时，会使胃壁扩张并且刺激胃黏膜上的受体。这也导致分泌活动增强。 Protein digestion starts in the stomach.The high acidity resulting from HCL secretions alters protein structure and exposes peptide bonds.It also converts pepsinogens to active enzymes (pepsins) that break the peptide bonds.
蛋白质消化在胃里开始。由于盐酸分泌导致的高酸度改变了蛋白质结构，使其暴露出肽链。盐酸也能激活胃蛋白酶原，将其转化为分解肽链的胃蛋白酶。 Ptotein fragments start accumulating,and this triggers secretion of gastrin——a hormone that stimulates the pepsinogen- and HCL-secreting cells even more.
蛋白质碎片开始积累，这会引发促胃液素的分泌——一种能刺激胃蛋白酶原和盐酸分泌细胞变得更多的激素。
Mucus and buffers (bicarbonate ions especially) keep HCL and pepsin from acting on proteins in the stomach wall. When something interferes with controls over their secretion , HCL is free to diffuse into the stomach’s lining.
粘液和缓冲液（特别是碳酸氢根离子）能避免盐酸和胃蛋白酶对胃壁上的蛋白质起作用。当某些物质干扰控制它们的分泌，盐酸就会自由扩散到胃的内膜。
There, it triggers the release of a chemical (histamine) from tissue cells.Among other things histamine stimulates more HCL secretion. A positive feedback loop is set up,and stomach tissues become damaged.
在那里，它会引起一种化学物质（组胺）从组织细胞中释放出来。除了别的之外，组胺刺激更多的盐酸分泌。一种正反馈循环被建立起来，胃组织受到损害。
If the tissue damage leads to bleeding in the stomach, the condition is called a the peptic ulcer. Think about this if you are sensitive to aspirin. Aspirin promotes inflammation of the stomach –largely by suppressing mucus and bicarbonate secretions.
如果组织损伤导致胃内出血，这种情况被叫做消化性溃疡。想到这你是否对阿司匹林感到很敏感，阿司匹林促进了胃炎症的引发，很大程度上是通过制止粘液和碳酸氢盐的分泌。
Stomach emptying. In the stomach, waves of contractions mix the chyme and build up force as they approach a sphincter at the start of the small intestine. The arrival of a strong contraction closes the sphincter, so most of the chyme is squeezed back. But a small amount moves into the small intestine. 胃空。在胃里，阵阵收缩使食糜混合，增强了它们接近小肠始端括约肌的力量。强有力的收缩紧邻括约肌，所以大部分食糜被挤压，但是很少量进入小肠。
Chyme’s volume and composition affect how fast the stomach empties. For example, large meals activate more stomach receptors, these call for more forceful contraction, and emptying speeds up.
食糜的量和组成成分影响胃变空的速度。例如，大餐会刺激更多胃感受器，这些命令造成更加强有力的收缩，胃变空的速度加快。
As another example, increased acidity (or fat content) in the small intestine stimulates hormone secretions that cause a slowdown in stomach emptying – so food isn’t moved along faster than it can be processed. Fear, depression, and other emotional upsets also trigger slowdowns.
再如，小肠内的胃酸（或脂肪含量）增加刺激激素的分泌，造成胃变空速度减慢。所以食物移动的速度不比它被加工的速度快。恐惧，沮丧，和其他不安情绪也会引起减速。
Only alcohol and a few other substances are absorbed across the stomach wall. Most substances move onward, to the small intestine
仅仅酒精和一些其他物质被吸收穿过胃壁，大多数物质向前移动到达小肠。
The Small Intestine
Carbonydrates, lipids(including fats), protines,and nucleic acids are digested by specific enzymes, then absorbed into the internal environment. Digestion is completed and most nutrients are absobed in the small intestine
小肠
糖类，脂类（包括脂肪），蛋白质和核酸被特殊的酶类消化，然后被吸收进入内部环境。消化被完成，并且大多数营养物质在小肠被吸收。
Secretions from the pancreas and liver assist in these tasks. Each day, the small intestine receives about nine liters of fluid from the stomach, liver, and pancreas. At least 95 percent is absorbed across an epithelial lining that is exposed to the intestinal lumen.
胰腺和肝脏的分泌物协助完成这些工作。每天，小肠能接收到9公升的液体来自胃，肝脏和胰腺，至少95%的液体透过暴露在肠道内腔的上皮层被吸收。
Processes of Digestion. Pancreatic enzymes are essential for digestion. They break down carbonydrates, proteins, nucleic acids, and fats. The pancreas also secretes bicarbonate, a buffer that helps neutralize HCL arriving from the stomach. (You may have heard of two other pancreatic secretions, insulin and glucagon, but these have roles in nutrition, not digestion.)
消化过程
胰腺酶对于消化是至关重要的。它们分解糖类，蛋白质，核酸和脂肪。胰腺也分泌碳酸氢盐，一种帮助中和来自胃的盐酸的缓冲剂（你或许也听说过两种其他的胰腺分泌物，胰岛素和胰高血糖素，但它们只在血糖调节中发挥作用而不是消化过程）。
Fat digestion depends on more than enzyme action. It depends also on bile, which is secreted continually by the liver. Bile contains bile salts, bile pigments, cholesterol, and lecithin (a phospholipid).
脂肪消化不只是依赖酶的活动。它也依赖于肝脏分泌的胆汁。胆汁包含胆汁盐，胆色素和卵磷脂（一种磷脂）。
It flows through ducts from the liver to the small intestine. When food isn’t moving through the gut, a sphincter closes off the main duct. Bile backs up into the saclike gallbladder, where it is stored and concentrated.
它通过管道从肝脏流入小肠。当食物没有到达小肠时，括约肌会封锁主要的管道。胆汁会备份到囊状的胆囊，在这里它被储存和集中。
By a process called emulsiification, bile salts speed up fat digestion. Most fats in our diet aretriglycerides. These are insoluble in water and tend to aggregate into large fat globules in the cheyme. 乳化这个过程，胆汁盐能加速脂肪的消化，更多的动植物油在我们的食物中是甘油三酯，在水里易于聚集成大的脂肪球的食糜里有不能溶解的脂肪。When movements of the intestinal wall agitate chyme, fat globules break up into smalldroplets, which become coated with bile salts. Because bile sales carry negative charges the coated droplets repel each other and stay separated. Tith suspension of fat droplets is the "emulsion'.
当脂肪转运到小肠，肠壁摇动食糜，脂肪球解散成被胆汁盐覆盖的小液滴。因为胆汁盐携带电荷，被覆盖着的液滴抵制别的液滴，彼此隔开。这些悬浮的脂肪液滴是乳状液。
Compared to fat globules, emulsion droplets give fat-digesting enzymes a much greater surface area to act upon. Thus triglycerides can be broken down much more rapidly to fatty acids and monoglycerides.
相酸和单糖比脂肪液滴，乳状液给予脂肪消化酶更大的表面区域去接触起作用。因此甘油三脂能更迅速地分解脂肪。
Processes of Absorption
The intestinal lining is one of the body' marvels.It has tdense folds,which are absorptive structures called villi [singular, villus]. Villi increase the surface area available for interactions with chyme.
吸收的过程
小肠的内层是身体的奇迹之一，它有稠密的皱褶，这种有吸收能力的结构被叫做绒毛【单一的，绒毛】。绒毛增加有效的表面区域，是为了与食糜相互作用。
Epithelial cells line these structures,and each cell has a crown of microvilli. Each microvillus is a threadlike projection of the plasma membrane.
Collectively,they greatly increase the surface area available for absorption.
上皮细胞排成这样的结构，每个细胞都有拥挤的微绒毛，每条微绒毛都是一条细长的突出等离子膜。共同的，它们大大的增加表面区域，利于有效的吸收。
By the time carbohydrate,protein,and lipid molecules are halfway through this elaborate tube,most have been broken down and digesed. Some of the products,incruding monosaccharides and amino acids,are absorbed in straightforward fation.So are water and mineral ions.
当碳水化合物，蛋白质，和脂质分子经过精心制作的管的途中的时候，大多数都被分解和消化。有些产物，包括单糖和氨基酸，被简单的方式吸收，剩下水和矿物离子。
Transport proteins in the plasma membrane of epithelial cells actively shunt them across the intestinal lining.Bycontrast,
bile salts assist the absorption of fatty acids and monoglycerides.These products
of fat digestion can diffuse across the lipid
bilayer of the plasma membrane of epithelial cells. shunt v. 移向一边
上皮细胞的等离子膜积极的将蛋白质移向一边，通向小肠内层，以达到运输蛋白质的目的。与之相比，胆汁盐帮助脂肪酸和单糖的吸收。脂质消化的产物可以扩散通过上皮细胞等离子膜的磷酸双分子层。
By a process called micelle formation,bile
salts combine with the products of the fat
digestion,forming tiny droplets[micelles]. Product molecules in the micelles continuously exchange places with product molecules that are dissolved in the
chyme.
这个过程叫微团的形成，胆汁盐结合脂质消化的产物，形成微小的液滴，微团中的产物分子不断交换地方，使产物溶解在食糜中。
When concentration gradients favor it,molecules diffuse out of micelles,out of
the chyme,and into epithelial cells.There,
fatty acids and monoglycerides recombine
as triglycerides.Then the triglycerides combine with proteins into particles that leave the cell by exocytosis and enter the
internal environment.
浓缩梯度证实了这过程，分子扩散出微团，再扩散出食糜，然后进入上皮细胞。在那里，脂肪酸和单糖重组成甘油三酯，接着，甘油三酯与蛋白质结合成微粒，以胞外分泌的方式离开细胞，进入内环境。
Once absorbed into the internal environment, glucose and amino acids enter blood vessels.The triglycerides enter
lymph vessels,which drain into blood vessels of the circulatory system.
一旦被吸收进内环境，葡萄糖和氨基酸进入血管，
甘油三酯进入淋巴管，这会排到血管进入循环系统。
Unit8
The Production Power of Hormones
With all the confidence of armchair diagnosticians,many of us like to equate the state of our health with the state of certain organs of the body which,for want of specifics,we summarily label as glands.
以夸夸奇谈的医家的自信口吻，我们许多人喜欢把我们的健康状态和我们身体的某些器官的状态等同起来，而对于这些器官，由于我们谈不出具体的东西，只是一言以蔽之地称为腺体。
Any indisposition not otherwise identifiable is explained away by the assertion that "my glands aren't working right."Unlike other amateur dicta in the field of medicine,this one occasionally proves accurate.
任何无法用其他办法识别的身体不适都以“我的腺体出了毛病”这一断言来作解释.”不像在医学领域的外行的权威意见，这件事偶然证明是准确的。
Certain glands do,in fact,exert enormous influence over the way we feel and the way we physically react.They wield this power through their control over that intriguing and not yet completely explored province of the body,its internal chemistry. 事实上，某些腺体确实在我们的感觉和身体反应上发挥着巨大的影响。它们是通过控制人体那神秘神秘而尚未完全探知的领域，即体内化学，来施展其威力。
By definition,a gland is any cell or organ that secretes some substance.Basically,the body contains two different types of glands,which are classified according to the way they secrete. 根据定义,腺体是分泌一些物质的某种细胞或器官。事实上,身体包含两种不同类型的腺体,它们根据分泌的方式进行分类。
One of these types is the exocrine gland,whose secretions move outward,to some body surface,whether it be the skin itself or,for example,the lining of the digestive respiratory tract. 其中一种是外分泌腺，其分泌物通常通过导管向外移动至一些身体表面,无论是皮肤本身，或比如说消化道或呼吸道粘膜。
The second type is the endocrine gland,whose secretions move inward,without benefit of ducts,into the bloodstream.
第二种类型是内分泌腺，其分泌物无需借助导管向内移动到血液中。
The endocrines are the great chemical regulators of bodily function.It is to these glands that the layman unwittingly refers when he blames some sort of glandular mischief as the cause of his ills.
内分泌是身体机能的主要化学调节系统。当门外汉指责一些类型的腺体的恶作剧造成他的疾病时，他无意提及的正是上述这些腺体。
The substances which are secreted by the endocrines,and which serve as their chemical messengers,are called hormones,from the Greek word hormon,which means "arouse to activity." 内分泌所分泌的物质,作为他们的化学信使,被称为激素，希腊语为荷尔蒙,意思是“激发活动。”
Along with the nervous system,the endocrine system serves as the majoy means of controlling the activities of the body. 除了神经系统之外,内分泌系统作为控制身体活动的主要方式。The nervous system is,so to speak,built for speed;it enables the body to adjust its internal processes rapidly,as changes are occurring in the environment. 可以说,神经系统是为了速度而产生的;随着环境的发生变化，它能使身体迅速调整内部的流程。
The endocrines,on the other hand,regulate continuing processes which have longer duration,including the body's growth,its sexual maturation and its ability to reproduce.
另一方面,内分泌调节持续过程持续时间更长的过程,包括身体的增长,其性成熟和繁殖能力。Only within the past century has any real understanding of the endocrine glands been achieved.Even today we are not certain how many there are. 只是在过去的一个世纪里，人们才对内分泌腺有了一些真正的理解。即使如今的我们不能确定有多少腺体。
Some are well known:the pituitary at the base of the brain;the thyroid gland in the neck;the four parathyroids lying behind the thyroid;the adrenals,perched atop the kidneys like miniature peakes caps; 一些是众所周知的:脑底部的垂体，在颈部的甲状腺，甲状腺后面的四个甲状旁腺，肾上腺，位于肾脏高处似微型鸭舌帽，
the insulin-making islets of Langerhans in the pancreas;the ovaries in the abdomen of the female,the testicles in the scrotum of the male.
胰腺中产生胰岛素的胰岛，女性腹部中的卵巢，男性阴囊中的睾丸。
The placenta,which feeds the unborn child,also behaves like an endocrine,manufacturing special chemicals essential to a successful pregnancy.
胎盘用来滋养未出生的胎儿，行为也就像是一个内分泌腺体，能够产生特殊的化学物质来成功受孕。
Recent studies have comfirmed that the brain itself acts as an endocrine ,since it,too,produces hormones .In fact,one part of the brain,the hypothalamus,is attached by both nerves and blood vessels to the pituitary gland.
最近的研究表明，大脑在自己可以充当激素的同时也可以生产激素。事实上，大脑的一部分，即通过神经也通过血管与垂体相连。
The pypothalamus secretes many hormones that regulate the release of the pituitary hormones；it is also a nervos center that controls the release of adrenaline from the adrenal gland.Both parts of the hypothalamus act together to keep the body in chemical balance.
下丘脑能分泌很多调节垂体激素分泌的激素：它同时也是控制肾上腺素从肾上腺分泌的神经中枢。下丘脑的各个部分一起保持身体的生态平衡。
Compared to such organs as the heart or the lungs,the endocrines seem to be ridiculously small and unimpressive.They are bits of tissue tucked away in obscure corners of the body;all of them together weigh no more than about five ounces.
相比较于像心脏和肺的器官，内分泌显得微不足道且不引人注目。他们是一小片隐藏在人体不起眼的角落中的组织;他们全部加起来还不足5盎司。
They make minute amounts of hormones that are rapidly circulated to all parts of the body .Nonetheless,in the widespread control which they exercise over the body,they are little giants.The key to their extraordinary power lies in the hormones they secrete --which include among them some of the most powerful and remarkable substances in the body.
他们产生微量的激素然后迅速散播到全身各处。尽管如此，在它们对身体所行使的广泛控制方面，它们是小小的巨人，他们非凡力量的关键在于他们所分泌的激素—其中包括人体中一些最强有力和最神奇的物质。
All hormones regulate one or more chemical reactions in the body, but they seem to work in many different ways. One hormone may alter cell membranes so that it is possible for glucose from the blood to enter the cells more freely
所有的激素都可以调节人体一个或者多个化学反应，但是他们似乎有不同的工作方法。激素通过改变细胞膜来让葡萄糖从血液更自由地进入细胞成为可能。
Anothher may change the spatial relation of enzymes, the chemcial catalysts resident in the cells, in order to speed up metabolic reactions . Still others may stimulate the production of other necessary chemcials within the cells. The precise mechanism of each hormone has not been completely identified , but many new facts are discovered each year.
另外一种，是通过改变酶的空间结构，即细胞固有的化学催化剂，来加速新陈代谢的反应。其他的激素仍然需要刺激其他细胞内必须的化学物质的生产。各自激素的行动的精确机制还没有完全确认，但是每年都有新的真相被发现。
A most important technical advance , which has made possible many of these discoveries , is called the radioimmunoassay method of measuring minute amounts of hormones in blood and tissue. This new laboratory technique has resulted in a radically new understanding of how hormones change cell functions .
最重要的科技进步，让很多关于激素的精密机制被发现成为可能，这是一种能测量血液和组织中微量的激素的叫放射免疫测定法的科技技术。这个新的实验室技术导致人们从根本上了解激素是怎么改变细胞功能的。
It seems that the hormone molecule acts like a key and fits into special locks that exist on cell membranes . Each tissue has its own kind of lock ,so a particular hormone , like estrogen , may influence the metabolism of cell in the breast but have little rffect on the cell of the eye. 激素分子像是一把钥匙且与细胞膜上存在的特定的锁融为一体。每个组织都有属于他们自己各种各样的锁，所以特定的激素，像雌激素，或对乳腺细胞的新陈代谢有影响但对眼睛细胞却没有什么影响。
The locks on the cell membranes are called hormone receptors. Once the hormone key enters the appropriate receptor lock , it opens a chemical pathway inside the cell which leads to metabolic changes . The chemcial pathway which seems to be most commonly used in many hormone-mediated reactions involves an enzyme called Cyclic AMP
这些细胞膜上的锁就被称为激素受体。一旦激素这把钥匙进入了合适的接收器之锁，就开启了细胞内通往代谢变化的化学通道。 在很多激素介导的反应中有共同作用的化学通道都涉及到了一种酶-环腺苷酸。
This enzyme is often refered to as the “second messenger” of the hormones. Whatever the specific steps prove to be ,one thing is clear : hormone activity must remain in delicate balance- like salt in the stew - or the entire body will be thrown out of kilter.
这种酶常常作为激素的“第二信使”。不管什么具体的步骤被证实，有一点是很明显的：激素的活动必须保持在微妙的平衡中--像是菜肴中的盐--否则整个机体都会失去平衡
The endocrine gland most familiar to the layman is the thyroid. Located at the base of the neck just below the Adam’s apple, this gland can be felt from the outside, and can thus be examined by the doctor more readily than any other;
外行人最熟悉的内分泌腺是甲状腺。它 位于脖子的底部，就在喉结的下面，这个腺体可能在外部被感觉到，因此，比起任何其它腺体，它都更容易被医生检查到； an enlargement or swelling of the thyroid may be apparent even by casual observation across a room. The hormones produced by the thyroid-iodine-protein compounds called thyroxin and triiodothyronine-exercise control over the rate at which food is converted into heat and energy in all the body’s cells. 甲状腺的变大或者肿胀是很明显的，即使通过一次简单的观察都能发现。甲状腺分泌的激素—被称为甲状腺激素和三碘甲腺原氨酸的碘-蛋白质复合物—能在身体各个细胞中控制食物转化为热量和能量的速度。Without sufficient thyroid hormones the individual feels constantly cold, drowsy andunable to accomplish anything without exerting considerable effort. His respiration is slow ,his heart rate is sluggish, his appetiteand sex functioning are both below par; sometimes he will gainweight in spite of a distinctly meager diet.没有充足的甲状腺激素，人就会一直感觉到寒冷、昏昏欲睡，不用很大的劲就做不了任何事情。他的呼吸会很慢、心跳迟缓、食欲和性功能都会低于常态；有时，明显吃得很少，但体重仍在增加。The opposite of this torpid syndrome of hypothyroidism, produced by an excess ofthyroid hormones. An individual with thiscondition will probably have a tendency to be nervous, jittery and overactive, with a pounding heart and labored respirations, able to gorge and yet still lose weight, as though all the body fires were burning out of control.与甲状腺功能减退这种麻木的综合征相反的是因甲状腺激素分泌过量导致的甲状腺功能亢进。患这种疾病的人会有紧张、焦虑和过度活跃的倾向，心脏跳动很激烈而且呼吸急促，食量很大但是体重还是下降，就像全身的火的燃烧失去了控制。
Most thyroid-deficiency diseases are caused either by a lack of iodine in thediet or by a curious immune response in which individualsdevelop antibodies thatattack and destroy their own thyroid glands. Next to diabetes, thyroid diseases are themost common endocrine ailments.大多数甲状腺缺乏疾病都是因为饮食中缺少碘或者因为自身产生的抗体攻击并破坏自己甲状腺的异常的免疫反应所导致的。居于糖尿病之后，甲状腺疾病是最常见的内分泌疾病。In sharp contrast to the easily approachablethyroid are the best hidden of all the endocrine glands: the tiny islands of insulin-producing cells scattered throughoutthe pancreas. Estimates of their number range from 250000 to 2.5 million. A Germananatomist, Paul Langerhans, first noticed them in 1869, and they known as the isletsof Langerhans in his honor.
与这个容易接近的甲状腺形成鲜明对比的是所有腺体中隐藏最好的腺体：分散在整个胰腺中的细小岛状的胰岛素生成细胞。它们在数量上的估算可从25万到250万。德国的解剖学家 Paul Langerhans 在1986年首次发现它们，所以为了纪念他，它们被命名为Langerhans小岛。 Each of these minute clumps of cells acts as a diminutive endocrine; together they make up, as it were, an organ within an organ, busily manufacturing their hormones and generally disregarding the pancreatic cells all around them, as though they were located in some completely different part of the body.每一个这种极小的细胞团就像是一个微小的内分泌物；它们在一起就组成了，像它本来一样，器官内的器官，忙碌地制造着它们的激素，并无视它们周围胰腺的细胞，就好像它们在身体内完全不同的两个部位一样。
Today we know that hormones manufactured in the islets of Langerhans-insulin and the more recently discovered glucagon and somatostatin-help to regulate the amount of sugar which is available at any given time For the cells to use for the production of
heat andenergy. Insulin acts by fitting the Receptor locks on muscle and fat cells,
opening an avenue for glucose entry.现在我们知道Langerhans小岛制造的激素—胰岛素和随更深入研究发现的胰高血糖素和生长抑素—帮助调节随时能共细胞使用来产生热量和能量的糖的含量。胰岛素通过结合肌细胞和脂肪细胞受体上的锁，来打开通路让葡萄糖进入。When the pancreas does not make enoughinsulin, or make it too slowly, the blood sugar goes up because muscle and fat cells cease to take up the glucose normally. In addition, some scientists believe that when a person with a hereditary disposition to diabetes puts on too much weight,
当胰腺没有生成足够的胰岛素，或者生成速度太慢，血糖就会升高，因为肌肉和脂肪细胞停止正常占用葡萄糖。此外，有些科学家认为当对糖尿病有遗传倾向的人体重过重时，
The fat-cell membranes are stretched and the insulin locks become distorted. Often,
if such a patient merely loses the excess weight, the blood sugar drops back to a normal level. 脂肪细胞的细胞膜会被伸展而且胰岛素的锁会变得歪曲。通常，如果这样一个病人只要减轻过去的体重，血糖就会回到普通的水平。
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