医学英语原文翻译1至5单元

1. 生理学是研究生物体正常功能的一门科学。它研究生物体如何进行各种活动，如何饮食，如何运动，如何适应不断改变的环境，如何繁殖后代。这门学科包罗万象，涵盖了生物体整个生命过程。生理学成功地解释了生物体如何进行日常活动，基于的观点是生物体好比是结构复杂而灵巧的机器，其操作受物理和化学规律控制。尽管从生物学整个范畴看，生物体某些活动过程是相似的，如基因编码的复制，但许多过程还是某些生物体群组特有的。鉴于此，将这门学科分成不同部分研究如细菌生理学，植物生理学和动物生理学是有必要的。Physiology is the study of the

functions of living matter. It is concerned with how an organism performs its varied activities: ho

w it feeds, how it moves, how it adapts to changing circumstances, how it spawns new generations . The subject is vast and embraces the whole of life. The success of physiology in explaining how organisms perform their daily tasks is based on the notion that they are intricate and exquisite mac hines whose operation is governed by the laws of physics and chemistry. Although some processes are similar across the whole spectrum of biology—the replication of the genetic code for example —many are specific to particular groups of organisms. For this reason it is necessary to divide the subject into various parts such as bacterial physiology, plant physiology, and animal physiology. 2. 正如要了解一个动物如何活动，首先需要

了解它的构成，要充分了解一个生物体的生理学活动就必须掌握全面的解剖学知识。一个生物体的各部分起着什么作用可通过实验观察得知。尽管我们对志愿者进行了许多重要的生理调查，但是实验条件需要精确控制，所以我们当前大多生理知识还是源于对其它动物如青蛙，兔子，猫和狗等的研究。当我们明确大多数动物物种的特定生理过程存在共同之处时，相同的生理原理适用于人类也是合理的。通过这种方法，我们获得了大量的知识，从而让我们对人类生理学有了更深入的了解，为我们有效治疗许多疾病提供了一个坚实的基础。To study how an animal works it is

first necessary to know how it is built. A full appreciation of the physiology of an organism must t herefore be based on a sound knowledge of its anatomy. Experiments can then be carried out to est ablish how particular parts perform their functions.

Although there have been many important physiological investigations on human volunteers, the n eed for precise control over the experimental conditions has meant that much of our present physi ological knowledge has been derived from studies on other animals such as frogs, rabbits, cats, an d dogs.

When it is clear that a specific physiological process has a common basis in a wide variety of anim al species, it is reasonable to assume that the same principles will apply to humans. The knowledg e gained from this approach has given us a great insight into human physiology and endowed us w ith a solid foundation for the effective treatment of many diseases.

The organization of the body3.

机体的基本组成物质是细胞，细胞结合在一

起形成组织。组织的基本类型有上皮组织，结缔组织，神经组织，肌组织，每类组织都有各自的特征。许多结缔组织中细胞量相对较少，但是有大量的细胞外基质。相比而言，光滑的肌组织由大量密密麻麻的肌细胞通过特定的细胞连接组成。各种器官如脑，心脏，肺，小肠和肝等由不同种类的组织聚集而成。这些器官是不同生理系统的组成部分。心脏和血管组成心血管系统；肺，器官，支气管，胸壁和膈肌组成呼吸系统；骨骼和骨骼肌组成骨骼肌系统；大脑，脊髓，自主神经和神经中枢以及周围躯体神经组成神经系统等等。

3. The building blocks of the body are the cells,

which are grouped together to form tissues. The principal types of tissue are epithelial, connective, nervous, and muscular, each with its own characteristics. Many connective tissues have relatively few cells but have an extensive extracellular matrix. In contrast, smooth muscle consists of densel y packed layers of muscle cells linked together via specific cell junctions.

Organs such as the brain, the heart, the lungs, the intestines, and the liver are formed by the aggreg ation of different kinds of tissues. The organs are themselves parts of distinct physiological system s. The heart and blood vessels form the cardiovascular system; the lungs, trachea, and bronchi toge ther with the chest wall and diaphragm form the respiratory system; the skeleton and skeletal musc les form the musculoskeletal system; the brain, spinal cord, autonomic nerves and ganglia, and per ipheral somatic nerves form the nervous system, and so on. 4. 细胞在形体和功能上差异很大，但是它们有某些共同的特征。

第一，细胞由一层薄膜也称细胞膜包被；第二，细胞能把大分子分解为小分子释放能量供活动所需；第三，在生命过程中某个阶段，细胞体内存在一个以脱氧核糖核酸(DNA)形式出现，包含基因信息的细胞核。4.

Cells differ widely in form and function but they all have certain common characteristics. First, th ey are bounded by a limiting membrane, the plasma membrane. Secondly, they have the ability to break down large molecules to smaller ones to liberate energy for their activities. Thirdly, at some point in their life history, they possess a nucleus which contains genetic information in the form of deoxyribonucleic acid (DNA). 5. 活体细胞不断转化物质。细胞分解葡萄糖和脂肪，为

自身生长和修复所需的蛋白质合成和运动等其它活动提供能量。这些化学变化统称为新陈代谢。把大分子分解为小分子的过程称为分解代谢，小分子合成大分子的过程称为合成代谢。

5. Living cells continually t

ransform materials. They break down glucose and fats to provide energy for other activities such a s motility and the synthesis of proteins for growth and repair. These chemical changes are collectiv ely called metabolism. The breakdown of large molecules to smaller ones is called catabolism and the synthesis of large molecules from smaller ones anabolism. 6. 细胞在进化过程中不断分化进行不同的功能活动。有些

细胞具有收缩能力（如肌细胞），有些可以传导电信号（如神经细胞）。进一步进化的细胞能够分泌不同物质如荷尔蒙（如内分泌细胞）或酶。胚胎发育过程中，分化的过程由于很多不同细胞来源于受精卵而再次发生。6. In the course of evolution, cells began to differentiate to se rve different functions. Some developed the ability to contract (muscle cells), others to conduct ele ctrical signals (nerve cells). A further group developed the ability to secrete different substances su ch as hormones or enzymes. During embryological development, this process of differentiation is re-enacted as many different types of cell are formed from the fertilized egg. 7. 大多数组织包含有不同的细胞类

型。比如，血液中含红细胞，白细胞和血小板。红细胞运输全身的氧气。白细胞在抵御感染时起重要作用，血小板是血液凝集过程中重要的成分。结缔组织有多种不同类型，但有一个共同特征，即细胞分布在丰富的细胞外基质中。神经组织含神经细胞和神经胶质细胞。

7. Most tissu

es contain a mixture of cell types. For example, blood consists of red cells, white cells, and platele ts. Red cells transport oxygen around the body. The white cells play an important role in defense a gainst infection and the platelets are vital components in the process of blood clotting. There are a number of different types of connective tissue but all are characterized by having cells distributed

within an extensive noncellular matrix. Nerve tissue contains nerve cells and glial cells. 8. 大型多细胞动物体的细胞不能产生氧气和营养物质，需

要直接从外界环境中获取。这些氧气和营养物质必须由血液运送到细胞。这是血液的主要功能之一，血液凭借心脏的泵血作用在血管内流动循环。

8. The cells of large multicellular animals cannot derive the oxygen and nutrients they need directl y from the external environment. These must be transported to the cells. This is one of the principa l functions of the blood, which circulates within blood

vessels by virtue of the pumping action of the heart. The heart, blood vessels, and associated tissue s form the cardiovascular system.

9. 心脏有四个腔，其中有两个心房，两个心室构成了一对并排存在的泵。右心室将去氧的血液泵至肺中，肺中的血液吸收空气中的氧气，而左心室把从肺回流来的有氧血液泵出至身体其它部位，供应给各组织。生理学家研究促使心脏跳动的因素，心脏如何泵送血液使其循环，心脏如何根据各组织所需分配血液。血浆和组织间的流动液体交换流入淋巴系统，最终回流到血液中。

9. The heart consists of four chambers, two atria and two ventricles, which form a pair of pumps a rranged side by side. The right ventricle pumps deoxygenated blood to the lungs where it absorbs oxygen from the air, while the left ventricle pumps oxygenated blood returning from the lungs to t he rest of body to supply the tissues.

Physiologists are concerned with establishing the factors responsible for the heartbeat, howthe hea rt pumps the blood around the circulation, and how it is distributed to perfuse the tissues according to their needs. Fluid exchanged between the blood plasma and the tissues passes into the lymphati

c system, which eventually drains back into the blood.

10. 机体进行各项活动所需的能量最终来源于呼吸。这一过程包括食物（主要是糖类和脂肪）的氧化，释放它们所含的能量。这一过程中，氧气来自于肺中的空气，经由血液到达全身各组织。组织呼吸活动中释放的二氧化碳由肺动脉中的血液运送至肺，然后呼气排出体外。需回答的基本问题如下：空气是如何进出肺的？呼吸的空气量如何适应机体所需？限制肺吸收氧气频率的因素是什么？

10. The energy required for performing the various activities of the body is ultimately derived fro m respiration. This process involves the oxidation of foodstuffs to release the energy they contain. The oxygen needed for this process is absorbed from the air in the lungs and carried to the tissues by the blood.

The carbon dioxide produced by the respiratory activity of the tissues is carried to the lungs by the blood in the pulmonary artery where it is excreted in the expired air. The basic questions to be ans wered include the following: How is the air moved in and out of the lungs? How is the volume of air breathed adjusted to meet the requirements of the body? What limits the rate of oxygen uptake in the lungs?

11. 机体所需营养物质来源于饮食。食物经口腔进入体内，在胃肠道内经酶将其分解成小分子物质。这些消化物通过肠壁吸收入血液，通过门静脉进入肝脏。经肝脏作用后，这些营养物质能够满足组织生长修复及能量需求。在消化系统部分，重要的生理学问题是：食物是如何消化的？食物如何被个体分解消化？个体营养物质如何吸收？食物如何在肠内转运的？未消化的残留如何从体内排出？11. The nutrients needed by

the body are derived from the diet. Food is taken in by the mouth and broken down into its compo nent parts by enzymes in the gastrointestinal tract. The digestive products are then absorbed into th e blood across the wall of the intestine and pass to the liver via the portal vein. The liver makes nu

trients available to the tissues both for their growth and repair and for the production of energy.

In the case of the digestive system, key physiological questions are: How is food ingested? How is it broken down and digested? How are the individual nutrients absorbed? How is the food moved through the gut? How are the indigestible remains eliminated from the body?

12. 肾脏主要功能是控制细胞外液体的形成。在这一过程中，肾脏也会把不可挥发的废物排出去。为行使这一功能，在排出之前，肾脏产生含有各种成分的尿液并将其暂时储存在膀胱中。这一部分主要的生理学问题是：肾脏如何调节血液中的成分？如何排出有毒废物？如何应对像脱水这样的应激反应？以及尿液可以存储和排出体外的机制是什么？

12. The chief function of the kidneys is to control the composition of the extracellular fluid. In the course of this process, they also eliminate non-volatile waste products from the blood. To perform these functions, the kidneys produce urine of variable composition which is temporarily stored in t he bladder before voiding.

The key physiological questions in this case are: how do the kidneys regulate the composition of t he blood? How do they eliminate toxic waste? How do they respond to stresses such as dehydratio n? What mechanisms allow the storage and elimination of the urine? The reproductive system13. 生殖是活生物体的一个基本特征。生殖腺产生专

门的性细胞，被称为配子。性生殖的核心是雌雄配子即精子和卵子的产生和融合，因此两个独立个体的基因特征融合而产生一个基因上与双亲不同的后代。 13. Reproduction is one of the fundamental characteristics of living

organisms. The gonads produce specialized sex cells known as gametes. At the core of sexual repr oduction is the creation and fusion of the male and female gametes, the sperm and ova (eggs), wit h the result that the genetic characteristics of two separate individuals are mixed to produce offspri ng that differ genetically from their parents.

14. 这一系统由骨、骨骼肌、关节和它们的相关组织组成。其主要功能是提供运动需要，维持姿势及呼吸运动。它也为内脏器官提供物理支持。这一部分，肌肉收缩机制是主要问题。内分泌系统和神经系统

14. This consists of the bones of the skeleton, skeletal muscles, joints, and their associated tissues. Its primary function is to provide a means of movement, which is required for locomotion, for the maintenance of posture, and for breathing. It also provides physical support for the internal organs . Here the mechanism of muscle contraction is a central issue. The endocrine and nervous systems 15.不同器官系统的活动需要协作和调节，以便共同作用满足机体需要。人体有两大调节系统：神经系统和内分泌系统。神经系统通过电信号迅速将信息传导给特定细胞。这样神经将电信号传递给骨骼肌以控制收缩。内分泌系统分泌化学物质―激素。激素通过血流到达施与调节作用的细胞。激素在许多不同器官中起着重要作用，在月经期调节和其它生殖方面尤其重要。15. The activities of the different organ systems need to be coordinated

and regulated so that they act together to meet the needs of the body. Two coordinating systems ha ve evolved: the nervous system and the endocrine system. The nervous system uses electrical sign als to transmit information very rapidly to specific cells. Thus the nerves pass electrical signals to t he skeletal muscles to control their contraction.

The endocrine system secretes chemical agents, hormones, which travel in the bloodstream to the cells upon which they exert a regulatory effect. Hormones play a major role in the regulation of m any different organs and are particularly important in the regulation of the menstrual cycle and oth er aspects of reproduction.

16. 免疫系统通过杀死入侵的有机体，清除致病或损伤细胞为机体提供防御功能。

16. The immune system provides the body’s defenses against infection both by

killing invading organisms and by eliminating diseased or damaged cells.

17. 虽然研究各器官如何行使功能很有益处，但我们必须认识到机体作为一个整体所做的活动依赖于各器官系统间错综复杂的相互作用。如果一部分无法正常工作，全身其它器官系统也会受到影响。例如，如果肾脏出现问题，内部环境的调节受损，结果导致其它器官系统功能紊乱。

17. Although it is helpful to study how each organ performs its functions, it is essential to recogniz

e that the activity o

f the body as a whole is dependent on the intricate interactions between the vari ous organ systems. If one part fails, the consequences are found in other organ systems throughout the whole body. For example, if the kidneys begin to fail, the regulation of the internal environme nt is impaired which in turn leads to disorders of function elsewhere.

18. 各种复杂机制共同作用调节细胞外液的形成，不同个体细胞有自身机制调节内在组成成分。尽管外界环境和动物活动不停变化，调节机制维持着体内环境的稳定。内部环境的稳定被称为稳态，它是机体能够正常发挥作用所必须的。 18. Complex mechanisms are at work to regulate the

composition of the extracellular fluid and individual cells have their own mechanisms for regulati ng their internal composition. The regulatory mechanisms stabilize the internal environment despit

e variations in both the external world and the activity o

f the animal. The process of stabilization o

f the internal environment is called homeostasis and is essential if the cells of the body are to funct ion normally.

19. 例如，心脏的跳动依赖于心肌细胞有节律的收缩。这一活动依赖于电信号，而电信号反过来依赖存在于细胞外和细胞内液体中钠和钾离子的浓度。如果细胞外液中钾离子过多，心肌细胞兴奋性增强，可能出现不规律的收缩。因此，要维持心脏正常跳动，细胞外液中钾离子的浓度就必须控制在一定范围内。

19. To take one example, the beating of the heart depends on the rhythmical contractions of cardia

c muscle cells. This activity depends on electrical signals which, in turn, depen

d on th

e concentrati on o

f sodium and potassium ions in the extracellular and intracellular fluids. If there is an excess o f potassium in the extracellular fluid, the cardiac muscle cells become too excitable and may contr act at inappropriate times rather than in a coordinated manner. Consequently, the concentration of potassium in the extracellular fluid must be kept within a narrow range if the heart is to beat norm ally.

20. 一天中，一个成人需要消耗约1千克食物，2-3升液体。以一个月计算，这相当于约30千克食物，60-90升液体。然而，一般来说，机体体重是基本不变的。这类个体可以说处于平衡状态。食物和液体的摄入量相当于正常机体活动消耗的能量加上尿液和粪便中丢失的能量。在一些情况下，如饥饿状态，摄入量与机体所需量并不相当，肌组织断裂，提供葡萄糖产生能量。蛋白质的摄入低于肌组织断裂的速度，机体处于负氮平衡。同样地，如果机体组织正处于生长期，如生长期的儿童，孕妇和早期训练阶段的运动员，那么蛋白质的日常摄入量比正常机体所需要的多。相反，此时个体处于正氮平衡。

20. In the course of a day, an adult consumes approximately 1 kg of food and drinks 2–3 liters of fl uid. In a month, this is equivalent to around 30 kg of food and 60–90 liters of fluid. Yet, in general, body weight remains remarkably constant. Such individuals are said to be in balance; the intake o f food and drink matches the amounts used to generate energy for normal bodily activities plus the losses in urine and feces.

In some circumstances, such as starvation, intake does not match the needs of the body andmuscle

tissue is broken down to provide glucose for the generation of energy. Here, the intake of protein i s less than the rate of breakdown and the individual is said to have a negative nitrogen balance. Eq ually, if the body tissues are being built up, as is the case for growing children, pregnant women a nd athletes in the early stages of training, the daily intake of protein is greater than the normal bod y turnover and the individual is in positive nitrogen balance.

21. 平衡的概念可以应用到机体的任何构成成分上，包括水和盐，而且平衡在机体调节其自身成分上是非常重要的。摄入必须等于所需，为维持机体平衡，任何多余的能量都必须排出。此外，因为机体的每种化学成分都有一个可取的浓度范围，控制机制维持这个范围。例如，两餐间血糖浓度大约为4-5mmol.l–1 . 进食后不久，血糖含量超过这一范围，刺激胰腺分泌胰岛素，降低浓度。随着葡萄糖浓度的下降，胰岛素分泌减少。在此情况下，循环胰岛素水平的改变都是为了使血浆中的葡萄糖维持在一个合适的范围内。这种调节称为负反馈机制。在胰岛素分泌期间，葡萄糖像肝糖原或脂肪一样被储存。

21. This concept of balance can be applied to any of the body constituents including water and salt and is important in considering how the body regulates its own composition. Intake must match re quirements and any excess must be excreted for balance to be maintained. Additionally, for each c hemical constituent of the body there is a desirable concentration range, which the control mechan isms are adapted to maintain.For example, the concentration of glucose in the plasma is about 4–5 mmol.l–1 between meals. Shortly after a meal, plasma glucose rises above this level and this stimu lates the secretion of the hormone insulin by the pancreas, which acts to bring the concentration do wn. As the concentration of glucose falls, so does the secretion of insulin. In each case, the change s in the circulating level of insulin act to maintain the plasma glucose at an appropriate level. This type of regulation is known as negative feedback. During the period of insulin secretion, the gluco se is being stored as either glycogen or fat.

22. 负反馈环是在机体出现紊乱时，将一些变量控制在限定范围内的一个控制系统。虽然上面的例子讲到血糖，但这一基本原则可以应用到其它生理变量中如体温、血压和血浆的渗透浓度。负反馈环需要一种能对不确定的变量做出反应而对其它生理变量不应答的传感器。因此，渗透压感受器应该能对机体体液渗透的变化而不是体温和血压的变化产生应答。感受器传递的信息必须和理想水平（系统的调定点）以比较者的身份，以某种方式进行比较。如果两者不相符，一个错误信号就会传递给效应器，效应器是一种能使变量保持在理想水平的系统。负反馈的这些特点可以通过检测一种简单的加热系统来理解。被控制的变量是室温，它可以由一个温度计检测到，效应器是一种加热器。当室温降低到调定点以下时，温度计就可以监测到温度的变化而开启加热器，对室内进行加温，直到室温升高到先前调好的调定点，加热器关闭。

23. a negative feedback loop is a control system that acts to maintain the level of some variable wi thin a given range following a disturbance. Although the example given above refers to plasma glu cose, the basic principle can be applied to other physiological variables such as body temperature, blood pressure, and the osmolality of the plasma. a negative feedback loop requires a sensor of so me kind that responds to the variable in question but not to other physiological bariables, thus an o smoreceptor should respind to changes in osmolality of the body fluids but not to changes in body temperature or blood pressure. the information from the sensor must be compared in some way wit h the desired level by some form of comparator. if the two do not match ,an error signal is transmit ted to an effector, a system that can act to restore the variable to its desired level .these f

eatures of negative feedback can be appreciated by examining a simple heating system .the control led variable is room temperature, which is sensed by a thermostat. the effector is a heater of some

kind .when the room temperature falls below the set point,the temperature difference is detected b y the thermostat which switches on the heater .this heats the room until the temperature reaches th

e per set level whereupon the heater is switched off.

23. 总而言之，机体实际上是由100万亿细胞有序组成了不同的功能结构，其中一些被称为器官。每个功能结构都在维持细胞外液稳态方面发挥其作用，这称之为内环境。只要内部环境处于正常状态，机体细胞继续生存并正常运行。每个细胞都从稳态中获益，反过来，每个细胞都为稳态做出贡献。这种相互作用促使机体持续自主运行，直至一个或多个功能系统不能正常运转。此时，机体所有细胞都会受损。功能极度异常会导致死亡，轻微的功能异常导致疾病的发生。

23.To sumarize, the body is actually a social order of about 100 trillion cells organized into differe nt functional structures,some of which are called organs.each functional structures its share to the maintenance of homeostatic conditions in the extracellular fluid,which is called the internal envir onment.as long as normal conditions are maintained in this internal environment ,the cells of the b ody continue to live and function properly.Each cell benefits from homeostasis,and in turn,each ce ll contributes its share toward the maintenance of homeostasis.This reciprocal interplay provides c ontinuous automaticity of the body until one or more functional systems lose their ability to contri bute their share of function.When this happens,all the cells of the body suffer.Extreme dysfunction leads to death;moderate dysfunction leads to sickness.

1.心动周期是一次心跳中的一系列活动。心动周期最简单的形式就是,是两个心房的同时收缩, 紧随其后，两个心室同时进行收缩。但是, 血液从心房进入心室和从心室进入动脉这两个过程之间有很大的差别。Th

e cardiac cycle is the sequence o

f events in one heartbeat. In its simplest form, the cardiac cycle is the simultaneous contraction of the two atria, followed a fraction of a second later by the simultan eous contraction of the two ventricles. There is, however, a significant difference between the mov ement of blood from the atria to the ventricles, and the movement of blood from the ventricles to t he arteries.

2.血液不间断地从静脉流入两个心房。随着大量的血液积聚, 血液的压力会打开左右房室瓣。两个心房里三分之二的血液被动地流入到心室中; 然后，心房收缩将剩余血液泵入心室。Blood is constantly flowin

g from the veins into both atria. As more blood accumulates, its pressure forces open the right and left AV valves. Two thirds of the atrial blood flows passively into the ventricles; the atria then cont ract to pump the remaining blood into the ventricles.

3.心房收缩后舒张，心室开始收缩。心室的收缩使血液施压于左右房室瓣的皮瓣并使其闭合; 同时，血液之力也打开了动脉和肺的半月瓣。随着心室的继续收缩, 它们把血液射入动脉。注意，进入动脉的血液必须被全部泵出。然后心室舒张, 同时血液继续流入心房，循环重新开始。

Following their contraction, the atria relax and the ventricles begin to contract. Ventricular contrac tion forces blood against the flaps of the right and left AV valves and closes them; the force of blo od also opens the aortic and pulmonary semilunar valves. As the ventricles continue to contract, th ey pump blood into the arteries. The blood that enters the arteries must all be pumped. The ventricl es then relax, and at the same time blood continues to flow into the atria, and the cycle will begin a gain.

4. 这里一个重要的不同点就是大部分血液是被动地从心房流入心室,但是所有注入动脉的血液均由心室主动射出。因此, 对生存来说，心室的正常工作远比心房的工作重要的多。

The important distinction here is that most blood flows passively from atria to ventricles, but all bl ood to the arteries is actively pumped by the ventricles. For this reason, the proper functioning of t he ventricles is much more crucial to survival than is atrial functioning.

5.收缩的另一个术语是心脏收缩。松弛的术语是心脏舒张。您可能比较熟悉这些术语，因为它们与血压读数相关。如果我们把这些术语应用到心脏血液循环中，我们就可以这样说, 心室收缩紧随心房收缩之后。换句话说，就是当心房收缩时, 心室舒张, 当心室收缩时, 心房舒张。

There is another term for contraction, and that is systole. The term for relaxation is diastole. You a re probably familiar with these terms as they relate to blood pressure readings. If we apply them to the cardiac cycle, we can say that atrial systole is followed by ventricular systole. Another way to put it is that when the atria are in systole, the ventricles are in diastole, and when the ventricles are in systole, the atria are in diastole.

6.您也许会问: 所有这些都发生在一次心跳中吗? 答案是肯定的。心脏血液循环就是由这一系列精确的活动组成，这些活动使血液从静脉流过心脏最后再注入动脉。

You may be asking: all this in one heartbeat? The answer is yes. The cardiac cycle is this precise s equence of events that keeps blood moving from the veins, through the heart and into the arteries.

7.心脏血液循环同时产生心音: 每一次心跳会有两个声音，用听诊器可以听见。第一声, 最大也最长, 是由心室收缩闭合房室瓣而引起的。第二声是由动脉和肺的半月瓣的闭合造成的。如果任一瓣膜闭合不全, 就会听见另外一个声音，称为―心脏杂音‖。The cardiac cycle also creates the heart sounds: each heartbeat produces two sounds, which can be heard with a stethoscope. The first sound, the loudest and longest, is caused by ventricular systole closing the AV valves. The second sound is caused by the closure of the aortic and pulmonary se mi-lunar valves. If any of the valves do not close properly, an extra sound called a heart murmur m ay be heard. 心脏的传导途径

8.心脏血液循环的一系列机械活动是由心肌的电活动调控。心肌细胞会自发收缩，即收缩并非由神经脉冲引起。心脏自行跳动，脑电脉冲沿一确定路径穿过心肌层。

The cardiac cycle is a sequence of mechanical events that is regulated by the electrical activity of t he myocardium. Cardiac muscle cells have the ability to contract spontaneously, that is, nerve imp ulses are not required to cause contraction. The heart generates its own beat, and the electrical imp ulses follow a very specific route throughout the myocardium.

9.心脏的自然起搏器是窦房结，它是位于右心房壁上的特化心肌细胞群。窦房结被认为是特化的是因为它有最快的收缩速度。

The natural pacemaker of the heart is the sinoatrial (SA) node, a specialized group of cardiac musc le cells located in the wall of the right atrium. The SA node is considered specialized because it ha s the most rapid rate of contraction, that is, it depolarizes more rapidly than any other part of the m yocardium.

10.收缩脉冲从窦房结运行到房室结，房室结位于心房间隔膜区下部。从窦房结和房室结到心房心肌层的其余部分的脉冲传导可引起心房收缩。

From the SA node, impulses for contraction travel to the atrioventricular (A V) node, located in the lower interatrial septum. The transmission of impulses from the SA node and AV node to the rest o

f the atrial myocardium brings about atrial systole.

11.心室间的上层隔膜内是希斯束, 它接收来自房室结的脉冲，并传给左右神经束支。脉冲从神经束支开始，沿着普肯野纤维到达心室心肌层的其他部分, 并引起心室收缩。心电图可以显示心房和心室的电子活动。 Within the upper interventricular septum is the Bundle of His (

AV bundle), which receives impulses from the AV node and transmits them to the right and left b undle branches. From the bundle branches, impulses travel along Purkinje fibers to the rest of the ventricular myocardium, and bring about ventricular systole. The electrical activity of the atria an

d ventricles is depicted by an electrocardiogram (ECG)

12.如果窦房结活动不正常, 房室结将启始心跳, 但速度较慢(每分钟50到60下)。希斯束也能引起心室跳动, 但是速度会慢地多(每分钟15 到40下)。这种情形会出现在某些心脏病中，是由心房到心室的脉冲传导被阻碍而引发的。 If the SA node does not function properly, the AV node will ini

tiate the heartbeat, but at a slower rate (50 to 60 beats per minute). The Bundle of His is also capab le of generating the beat of the ventricles, but at a much slower rate (15 to 40 beats per minute). T his may occur in certain13.心率失常是不规则的心跳; 它们的影响范围小到对人体无害大到威及生命。几乎每个人不时都会感受心悸。这些通常都不太严重, 而且可能是因为过多摄入了咖啡因, 尼古丁或酒精造成的。然而严重的是心室纤维颤动, 是一种非常迅速的、不协调的、完全无法泵出血液的心室悸实

Arrhythmias are irregular heartbeats; their effects range from harmless to life-threatening. Nearly everyone experiences heart palpitations from time to time. These are usually not serious, and may be the result of too much caffeine, nicotine, or alcohol. Much more serious is ventricular fibrillatio n, a very rapid and uncoordinated ventricular beat that is totally ineffective for pumping blood.

心率

14.一个健康的成年人安静时的心跳一般在每分钟60至80下，是窦房结去极化的速度。一个小孩正常心跳为每分钟100下，一个刚出生的婴儿的心跳多达每分钟120下；一个快要出生的胎儿的心跳则在每分钟140下左右。这些较快的心率与年龄无关，与体型则关系密切：体型越小，新陈代谢的速率就会越快，同样心率也会越高。这样的例子可以从不同体形的动物得到启示：老鼠的心率在每分钟200次左右，而大象的心率在每分钟30次左右。 A healthy adult has a resting heart rate (pulse) of 60 to 80beats per minute, which is the rate of depolarization of the SA node. A child’s normal heart rate may be as high as 100 beats per min ute, that of an infant as high as 120, and that of a near-term fetus as high as 140 beats per minute. These higher rates are not related to age, but rather to size: the smaller the individual, the higher th e metabolic rate and the faster the heart rate.Parallels may be found among animals of different siz es; the heart ra te of a mouse is about 200 beats per minute, and that of an elephant about 30 beats per minute.

15.让我们回到成人心率这个问题上来，设定一个人拥有良好的健康状况。正如你所知，一个身体状态良好的运动员的心率较低。那些篮球运动员的脉搏在每分钟50次左右，马拉松运动员的脉搏在每分钟35到40次。要搞清楚这一点，首先要记住心脏是一个肌性器官。当我们充分锻炼我们骨骼肌的时候，它们变得更加强壮、高效。这点同样适用于我们的心脏：持续的运动使得心脏泵血更加有力。

心输出量Let us return to the adult heart rate, and consider the person who is in excellent physical condition. As you may know, well-conditioned athletes have low resting pulse rates.

Those of basketball players are often around 50 beats per minute, and the pulse of a marathon runn er often ranges from 35 to 40 beats per minute. To understand why this is so, remember that the he art is a muscle.When our skeletal muscles are exercised, they become stronger and more efficient. The same is true for the heart; consistent exercise makes it a more efficient pump, as you will see i n the next discussion.

16. 心输出量是指每分钟心室泵出的血液量。我们的身体时刻需要一定量的心脏供血，将氧气输送到身体的各个组织，同时清除身体产生的废物。在锻炼过程中，心脏供血量增加，以满足身体对氧气的需求。讨论过静息状态下的心输出量以后，我们再回到运动时心输出量这个话题上来。

Cardiac output is the amount of blood pumped by a ventricle in one minute. A certain level of card iac output is needed at all times to transport oxygen to tissues and to remove waste products. Duri ng exercise, cardiac output must increase to meet the body’s need for more oxygen. We will return to exercise after first considering resting cardiac output.

17.为了计算心输出量，我们必须知道心率和每次心跳所泵出的血液量。心脏供血量这一术语是指心室每次跳动所泵出的血液量。人在静息状态下，每次心跳的供血量均在60到80毫升。下面这个简单的公式能使我们很容易计算出心输出量： In order to calculate cardiac output, we must know the pulse ra

te and how much blood is pumped per beat. Stroke volume is the term for the amount of blood pu mped by a ventricle per beat; an average resting stroke volume is 60 to 80 ml per beat. A simple fo rmula then enables us to determine cardiac output:

Cardiac output ＝Stroke volume × pulse (heart rate)

18.我们假定人安静时的心室跳动一次的供血量为70毫升，其心率为每分钟70次：心输出量＝ 70ml × 70 bpm（每分钟脉搏次数）心输出量＝4900 ml/m (大约5 L)

Let us put into this formula an average resting stroke volume, 70 ml, and an average resting pulse, 70 beats per minute (bpm): Cardiac output ＝ 70 ml × 70 bpm Cardiac ou tput ＝ 4,900 ml per minute (approximately 5 liters)

19.当然心输出量的多少会随着人体型的大小而变，但人在静息状态下的心输出量是每分56升。 Naturally, cardiac output varies with the size of the person, but the average resting cardiac o utput is 5 to 6 liters per minute.

20.现在我们再看一下运动员, 我们就可以清楚地知道为什么运动员在静息状态下，心率较常人低。我们假定人在静息状态下的心脏供血量为每分钟5 L，运动员心率为每分钟50次：心输出量＝每博量×心率 5,000/50＝每搏量 100 ml＝每搏量

If we now reconsider the athlete, you will be able to see precisely why the athlete has a low resting pulse. In our formula, we will use an average resting cardiac output (5 liters) and an athlete’s puls e rate (50):

Cardiac Output ＝Stroke volume × pulse 5,000/50＝Stroke volume 100 ml＝Stroke volume

21.我们注意到静息状态下运动员的心脏供血量明显高于常人。运动员的强有力的心脏每次跳动能为身体提供更多血液。因此，静息状态下他们保持一个较低的心率。 Notice that the athlete’s resting stroke volume is significantly higher than the average. The athlete’s more efficient heart pumps more blood with each beat, and so can maintain a normal resting cardiac output with fewer beats.

22.现在我们再考虑一下心脏对运动作何反映。人在运动的过程中心率会加快，心输出量也会相应增加。心输出量的增加是斯塔林心脏定律的结果，定律指出心肌纤维越伸展，它们的收缩越强。运动过程中，更多的血液通过静脉回流的方式回到心脏。静脉回流量的增加就会促使心肌层的伸展，这样心室收缩有力，泵出更多的血液，增加心脏供血量。因此，运动时，心脏供血量的计算公式如下：

kinds of heart disease in which transmission of impulses from the atria to the ventricles is blocked.

心输出量＝每搏量×心率心输出量＝ 100 ml ×100 bpm 心输出量＝10,000 ml (10 liters) Now let us see how the heart responds to exercise. Heart rate

(pulse) increases during exercise, and so does stroke volume. The increase in stroke volume is the result of Starling’s Law of the Heart, which states that the more the cardiac muscle fibers are stretched, the more forcefully they contract. During exercise, more blood returns to the heart; th is is called venous return. Increased venous return stretches the myocardium of the ventricles, whi ch contract more forcefully and pump more blood, thereby increasing stroke volume. Therefore, d uring exercise, our formula might be the following: Cardiac output ＝Stroke volume × pulse Cardiac output ＝100 ml × 100 bpm Cardiac output ＝ 10,000ml(10 liters)

23.运动时心输出量几乎是前面我们计算的静息状态下的两倍，而这并非异常。剧烈运动时，一个健康年轻人每分钟的心输出量可以增加到他安静时的４倍；一个马拉松运动员的心输出量可以达到他安静时的６倍甚至更多；这是因为马拉松运动员拥有强有力的心脏。

This exercise cardiac output is twice the resting cardiac output we first calculated, which should n ot be considered unusual. The cardiac output of a healthy young person may increase up to four ti mes the resting level during strenuous exercise. This exercise cardiac output is twice the resting ca rdiac output we first calculated, which should not be considered unusual. The cardiac output of a h ealthy young person may increase up to four times the resting level during strenuous exercise.

心率的调节

24.虽然心脏自行跳动并保持其跳动，但心脏收缩的频率可根据情况的不同而发生变化。神经系统可以调节心脏收缩的力度并控制心率的必要变化。 Although the heart generates and maintains its own beat, the rate of contraction can be chang ed to adapt to different situations. The nervous system can and does bring about necessary changes in heart rate as well as in force of contraction.

25.脑髓质有两个心血管控制中心：加速中枢和抑制中枢。两中枢通过自主神经向心脏传送神经脉冲。自主神经系统可以分为交感神经和副交感神经两大股。加速中枢产生的交感脉冲通过交感神经传输到心脏，加快心脏的跳动速率和收缩力度。抑制中枢产生的副交感脉冲通过迷走神经传输到心脏，降低心脏跳动的速率。

The medulla of the brain contains the two cardiac centers, the accelerator center and the inhibitory center. These centers send impulses to the heart along autonomic nerves. The autonomic nervous system has two divisions: sympathetic and parasympathetic. Sympathetic impulses from the accele rator center along sympathetic nerves increase heart rate and force of contraction. Parasympathetic impulses from the inhibitory center along the vagus nerves decrease the heart rate.

26.我们下一个问题是脑髓质接受了什么信息才引起这些变化呢？既然心脏泵出血液，维持血压正常就很重要了。血液含氧气，身体各组织必须不停地获得这种含氧血。因此，血压和血液中含氧量的变化就会刺激心率产生相应的变化。

Our next question might be: what information is received by the medulla to initiate changes? Sinc e the heart pumps blood, it is essential to maintain normal blood pressure. Blood contains oxygen, which all tissues must receive continuously. Therefore, changes in blood pressure and oxygen leve l of the blood are stimuli for changes in heart rate.

心输出量＝每搏量×心率心输出量＝ 100 ml ×100 bpm 心输出量＝10,000 ml (10 liters) Now let us see how the heart responds to exercise. Heart rate

(pulse) increases during exercise, and so does stroke volume. The increase in stroke volume is the result of Starling’s Law of the Heart, which states that the more the cardiac muscle fibers are stretched, the more forcefully they contract. During exercise, more blood returns to the heart; th

is is called venous return. Increased venous return stretches the myocardium of the ventricles, whi ch contract more forcefully and pump more blood, thereby increasing stroke volume. Therefore, d uring exercise, our formula might be the following: Cardiac output ＝Stroke volume × pulse Cardiac output ＝100 ml × 100 bpm Cardiac output ＝ 10,000ml(10 liters)

23.运动时心输出量几乎是前面我们计算的静息状态下的两倍，而这并非异常。剧烈运动时，一个健康年轻人每分钟的心输出量可以增加到他安静时的４倍；一个马拉松运动员的心输出量可以达到他安静时的６倍甚至更多；这是因为马拉松运动员拥有强有力的心脏。

This exercise cardiac output is twice the resting cardiac output we first calculated, which should n ot be considered unusual. The cardiac output of a healthy young person may increase up to four ti mes the resting level during strenuous exercise. This exercise cardiac output is twice the resting ca rdiac output we first calculated, which should not be considered unusual. The cardiac output of a h ealthy young person may increase up to four times the resting level during strenuous exercise.

心率的调节

24.虽然心脏自行跳动并保持其跳动，但心脏收缩的频率可根据情况的不同而发生变化。神经系统可以调节心脏收缩的力度并控制心率的必要变化。 Although the heart generates and maintains its own beat, the ra

te of contraction can be changed to adapt to different situations. The nervous system can and does bring about necessary changes in heart rate as well as in force of contraction.

25.脑髓质有两个心血管控制中心：加速中枢和抑制中枢。两中枢通过自主神经向心脏传送神经脉冲。自主神经系统可以分为交感神经和副交感神经两大股。加速中枢产生的交感脉冲通过交感神经传输到心脏，加快心脏的跳动速率和收缩力度。抑制中枢产生的副交感脉冲通过迷走神经传输到心脏，降低心脏跳动的速率。

The medulla of the brain contains the two cardiac centers, the accelerator center and the inhibitory center. These centers send impulses to the heart along autonomic nerves. The autonomic nervous system has two divisions: sympathetic and parasympathetic. Sympathetic impulses from the accele rator center along sympathetic nerves increase heart rate and force of contraction. Parasympathetic impulses from the inhibitory center along the vagus nerves decrease the heart rate.

26.我们下一个问题是脑髓质接受了什么信息才引起这些变化呢？既然心脏泵出血液，维持血压正常就很重要了。血液含氧气，身体各组织必须不停地获得这种含氧血。因此，血压和血液中含氧量的变化就会刺激心率产生相应化。

Our next question might be: what information is received by the medulla to initiate changes? Sinc e the heart pumps blood, it is essential to maintain normal blood pressure. Blood contains oxygen, which all tissues must receive continuously. Therefore, changes in blood pressure and oxygen leve l of the blood are stimuli for changes in heart rate.

27.压力感受器和化学受体位于颈动脉和主动脉弓。位于颈动脉窦和主动脉窦的压力感受器可检测血压的变化。位于颈动脉体和主动脉体内的化学受体可检测血液中含氧量的变化。颈动脉受体的感觉神经是舌咽神经；主动脉弓受体的感觉神经是迷走神经。如果我们把上面这些事实集中在一个特例中，我们就可以看出心脏调节是一种反射。

Pressoreceptors and chemoreceptors are located in the carotid arteries and aortic arch. ors in the ca rotid sinuses and aortic sinus detect changes in blood pressure. Chemoreceptors in the carotid bodi es and aortic body detect changes in the oxygen content of the blood. The sensory nerves for the c arotid receptors are the glossopharyngeal nerves; the sensory nerves for aortic arch receptors are th e vagus nerves. If we now put all these facts together in a specific example, you will see that the r egulation of heart rate is a reflex.

28.一个处于卧位的人突然变为站位，或许会感到一阵稍微的头晕，这是因为脑部血压突降的缘故。位于颈动脉窦的压力感受器可测得这种血压的降低——注意这些感受器处于到达大脑的―途中‖，一个关键部位。压力感受器发出的脉冲沿舌咽神经到达脑髓质，刺激加速中枢。加速中枢生成的脉冲通过交感神经到达窦房结、房室结和心室的心肌层。随着心率和心脏跳动的力度增强，到达大脑的血压升高到正常水平，头晕症状消失。当到达大脑的血压恢复正常后，心脏接收来自抑制中枢的副交感神经脉冲，它们沿迷走神经到达窦房结和房室结。这些副交感神经脉冲减缓心率至正常休息频率。

A person who stands up suddenly from a lying position may feel light-headed or dizzy for a few m oments, because blood pressure to the brain has decreased abruptly. The drop in blood pressure is detected by pressoreceptors in the carotid sinuses— notice that they are ―on the way‖ to the brain, a very strategic location. Impulses generated by the pressoreceptors travel along the glossopharyn geal nerves to the medulla, and stimulate the accelerator center.

The accelerator center generates impulses that are carried by sympathetic nerves to the SA node, A V node, and the ventricular myocardium. As heart rate and force increase, blood pressure to the br ain is raised to normal, and the sensation of light-headedness passes. When blood pressure to the b rain is restored to normal, the heart receives more parasympathetic impulses from the inhibitory ce nter along the vagus nerves to the SA node and A V node

29.在血液含氧量减少形成刺激生成的反射中，心脏也是一个效应器。血液一离开心脏，处于关键位置的主动脉受体即可检测像血氧含量减少这样重大的变化。这种情形下的反射弧将会是：1）主动脉化学受体；2）迷走神经；3）脑髓质中的加速中枢；4）交感神经；5）心脏。心脏通过增加其跳动的速率和收缩的力度循环更多的氧气，克服身体组织的缺氧症状。人体生理学The heart will also be the effector in a reflex stimulated by a decrease in the oxygen content of the blood. The aortic receptors are strategically located so as to detect such an important change as so on as blood leaves the heart. The reflex arc in this situation would be:

1) aortic chemoreceptors, 2) vagus nerves (sensory), 3) accelerator center in the medulla, 4) sy mpathetic nerves, 5) the heart, which will increase its rate and force of contraction to circulate mor e oxygen to correct the hypoxia.

Body Temperature and Metabolism

生命中的每时每刻，人体细胞总是不停地分解食物分子，以获取细胞代谢所需的三磷酸腺苷。当然，人们意识不到细胞呼吸过程，但却会意识到其产物---热。的确，人体总是热的，而且即便在环境温度变化幅度较大的范围内，人体体温也得以精确的调节。

During every moment of our lives, our cells are breaking down food molecules to obtain ATP for energy-requiring cellular processes.

Naturally, we are not aware of the process of cell inspiration but we may be aware of the products, energy in the form of heat. The human body is indeed warm, and its temperature is regulated very precisely, even in a wide range of environmental temperatures.

Body Temperature

人体正常体温范围是96.5-99.5?F (36-38?C)，平均体温为98.6? F (37?C)。在一天24小时期间，人体温度波动幅度为1-2?F，睡眠期间体温最低。

The normal range of h u m a n b o d y temperature is 96.5-99.5 o (36-38o with an F C), aver ag e o f 9 8 .6 o F (37o C). Within a 24hour period, an individual’s temperature fluctuates 1-2 o with F the lowest temperatures occurring during sleep.

然而，在年龄段两端的人群，其体温调节精确程度都不如青少年或青年人。婴儿，相对于其体积来说，皮肤暴露面多，散热较快。老年人的体温维持机制功能不像以前那样高效，不可能会对环境温度变化做出快速、有效的调整。因此，在照顾年幼、年长的病人时，牢记这一点特别重要。

At either end of the age spectrum, however, temperature regulation may not be as precise as it is in older children or younger adults. Infants have more surface area (skin) relative to volume, and are likely to lose heat more rapidly. In the elderly, the mechanisms that maintain body temperature may not function as efficiently as they once did, and changes in environmental temperature may not be compensated for as quickly or effectively. This is especially important to remember when caring for patients who are very y o u n g o r v e r o l d .

Heat Production

胞呼吸是由食物中释放能量以产生三磷酸腺苷的过程，同时也产生了能量产物之一--热。虽然细胞呼吸一刻不停，但影响其速率的有多个因素：

Cell respiration, the process that releases energy from food to produce ATP, also produces heat as one of its energy products. Although cell respiration takes place constantly, there are many factors that influence the rate of this process:

甲状腺分泌的甲状腺激素(和T3)会增加细胞呼吸和产热速率。甲状腺的分泌受体内能量代谢速率调控。代谢速率减缓时，甲状腺会受到刺激以致分泌更多的甲状腺素。当甲状腺素使细胞呼吸速率加快时，负反馈机制会抑制其进一步分泌直到代谢速率再次放缓。因而，每当细胞呼吸速率需要加快时，就会分泌甲状腺素，而且甲状腺素或许是日常最重要的能量调节者。

1. The hormone thyr?xine (甲状腺素and T3), produced by the thyroid gland, increases the rate of cell respiration and heat production. The secretion

of thyroxine is regulate d by the body’s rate of energy production, the metabolic rate, itself. When the metabolic rate decreases, the thyroid gland is stimulated to secrete more t h y r o x i n e .As thyroxine increases the rate of cell respiration, a negative feedback mechanism inhibits further secretion until metabolic rate decreases again. Thus, thyroxine is secreted whenever there is a need for increased cell

respiration, and is probably the most important regulator of day-to-day energy production.

在紧张状态下，肾上腺髓质会分泌出肾上腺素和去甲肾上腺素，而且交感神经系统会更加兴奋。肾上腺素提高了器官的细胞呼吸速率，特别是心脏、骨骼肌、肝脏等。交感刺激也会增强这些器官的活动。由于紧张所需增加的三磷酸腺苷的生成，同时也意味着产热量会大大增加

2. In stress situations, epinephrine and norepinephrine are secreted by the adrenal medulla, and the sympathetic nervous system b e c o m e s m o r e a c t i v e .Epinephrine increases the rate of cell respiration, especially in organs such as the h e a r t , s k e l e t a l m u s c l e s , a n d l i v e r. Sympathetic stimulation also increases the activity of these organs. The increased production of ATP to meet the demands of the stress situation also means that more heat will b e p r o d u c e d . 通常活跃的器官(生成三磷酸腺苷)是人体休息状态下热量的主要来源。例如，骨骼肌，经常处于轻微的收缩状态（肌紧张）。因为即便轻微的收缩就需要三磷酸腺苷，那么肌肉也会产热。这大约占人体休息状态下所产热量的25%，运动时会产生更多的热量，也就会生成更多的三磷酸腺苷。肝脏是持续活跃的另一器官，生成的三磷酸腺苷向肝脏多个功能提供能量。由此，肝脏所产生的热量占人体休息状态下总产热量的20%。这些活跃器官产生的热由血液传送到身体的各个部位。当相对较凉的血液在流经肌肉和肝脏等器官时，这些器官所产生的热会转移到血液中，使血液变暖。变暖的血液流到身体的其它部位时，将热分散。

3. Organs that are normally active (producing A TP) are significant sources of heat when the body is at rest. The skeletal muscles, for example, are usually in a state of slight contraction called muscle tone.

Since even slight contraction requires A TP, the muscles are also producing heat. This amounts to about 25% of the total body heat at rest, and much more during exercise when more ATP is produced. The liver is another organ that is continually active, producing ATP to supply energy for its many functions. As a result, the liver produces as much as 20% of the total body heat at rest.The heat produced by these active organs is dispersed throughout the body by the blood. As the relatively cooler blood flows through organs such as the muscles and liver, the heat they produce is transferred to the blood, warming it. The warmed blood circulates to other areas of t h e b o d y, d i s t r i b u t i n g t h i s h e a t . 食物的摄入也增加产热，这是因为消化道新陈代谢活动增加了。在消化器官因蠕动和消化酵合成而生成三磷酸腺苷的同时，产生了热。

4. The intake of food also increases heat production, because the

metabolic activity of the digestive tract is increased. Heat is generated as the digestive organs produce ATP for peristalsis and for the synthesis of digestive e n z y m e s .

5. 人体体温的变化也会影响代谢率和产热。当一个人发热，体温异常升高时，从临床上讲，体温变化就显得重要了。较高的体温会增加代谢率，代谢率会促进产热，使体温升得更高。因而此，高烧会引发持续不断的产热恶性循环

Changes in body temperature also have an effect on metabolic rate and heat production. This becomes clinically important when a person has a fever, an abnormally high body temperature. The higher temperature increases the metabolic rate, which increases heat production and elevates body temperature further. Thus, a high fever may trigger a vicious cycle of ever-increasing heat production.

Heat Loss

人体散热途径是经皮肤、呼吸道，少量经尿道和消化道散热。

The pathways of heat loss from the body are the skin, respiratory tract, and to a lesser extent, the urinary and digestive tracts.

Heat Loss Through the Skin

由于皮肤包裹着人体，所以大部分体热经皮肤散发到环境中。当环境温度低于人体体温(通常如此)时，散热不可避免。散热量取决于流经皮肤的血流和汗腺的活动

Since the skin covers the body, most body heat is lost from the skin to the environment. When the environment is cooler than body temperature (as it usually is), heat loss is unavoidable. The amount of heat that is lost is determined by blood flow through the skin and by the activity of sweat glands.

流经皮肤的血流因辐射、传导、对流会影响到散热量。辐射是指将体热散发到较冷的空气中，就像散热器给室内空气加热一样。传导是指体热传至较凉的物体，譬如接触皮肤的衣物等。对流是指气流将皮肤表面的热气带走，有利于散热。这就是天热时风扇会让我们感到凉快的原因。

Blood flow through the skin influences the amount of heat lost by the processes of radiation, conduction, and convection(对流传热). Radiation means that heat from the body is lost to cooler air, much as a radiator warms the air within a room. Conduction is the loss of heat to cooler objects, such as clothing, that touch the skin. Convection means that air currents move the warmer air away from the skin surface and facilitate the loss of heat; this is why a fan makes us feel cooler on hot days. 皮肤的温度和散热决定于流经皮肤的血流。皮肤小动脉收缩或扩张来减少或增

加血流。血管收缩会减少流经皮肤的血液量，因而减少散热。皮肤血管扩张会增加流向身体表层的血流和散热量

The temperature of the skin and the subsequent loss of heat are determined by blood flow through the skin. The arterioles in the dermis may constrict or dilate to d e crease b l o o d f l o w. Vasoconstriction decreases blood flow through the dermis, and thereby decreases heat loss. Vasodilation in the dermis increases blood flow to the body surface and loss of heat to the e n v i r o n m e n t .

经皮肤散热的另一方式是排汗。小汗腺将汗液分泌到皮肤表面，多余的体热将汗液蒸发。这就好像把自来水倒入热锅，随着热气将水蒸发，锅的温度很快会冷却下来。虽然排汗没有那么明显(水蒸汽看不到)，但原理是相同的

The other mechanism by which heat is lost from the skin is sweating. The eccrine sweat glands secrete sweat (water) onto the skin surface, and excess body heat evaporates the sweat. Think of running water into a hot frying pan; the pan is rapidly cooled as its heat vāporizes the water. Although sweating is not quite as dramatic (no visible steam), the principle is just the same.当周围空气湿度低时，排汗效率最高。湿度是大气所含最大水蒸气量的百分值。湿度值90%是指空气中的水蒸气饱和度为90%，无力容纳更多的水蒸气。在这样情况下，汗液不易蒸发，既便分泌再多的汗，也只会停留在皮肤表面。如果湿度值为40%时，空气会容纳更多的水蒸气，汗液会迅速从皮肤表面蒸发，从而带走多余的体热。Sweating is most efficient when the humidity of the surrounding air is low. Humidity is the percentage of the maximum amount of water vapor the atmosphere can contain. A humidity reading of 90% means that the air is already 90% saturated with water vapor and can hold little more. In such a situation, sweat does not readily evaporate, but rather, remains on the skin even as more sweat is secreted. If the humidity is 40%, however, the air can hold a great deal more water vapor, and sweat evaporates quickly from the skin surface, removing excess body heat.虽然排汗是一个非常有效的散热机制，但也有不利之处。这是因为人体为了散热就要失去体内水分。出汗时失水过快会导致脱水，因此所失去的水分必须通过饮用液体来进行补充。Although sweating is a very effective mechanism of heat loss, it does have a disadvantage in that it requires the loss of water in order to also lose heat. Water loss during sweating may rapidly lead to dehydration, and the water lost must be replaced by drinking fluids.小量的散热还现于―无知觉失水‖。因为皮肤不是一个塑料袋，具有一定的渗透性，小量的水分经皮肤散开并由体热将其蒸发。然而，与出汗相比，不无知觉失水是次要的散热途径Small amounts of h eat are also lost in what is called ―insensible water loss‖. Since the skin is not like a plastic bag, but is somewhat permeable to water, a small amount of water diffuses through the skin and is evaporated by body heat. Compared to sweating, however, insensible water loss is a minor source of heat loss.当呼吸道粘膜蒸发掉其上皮表层的一些水分时，热量就从经呼吸道丧失了。蒸气呼出，并带走些许热量Heat is lost from the respiratory tract as the warmth of the respiratory mucosa evaporates some water from the living epithelial surface. The water vapor formed is exhaled, and a small amount of heat is lost.如果动物没有大量汗腺，比如狗，在炎热的天气下，就会经常―气喘‖。气喘是空气进出上呼吸道的剧烈运动，上呼吸道的热表层蒸发掉大量的水分。通过这种方式，动物排出大量的体热Animals such as dogs that do not have numerous sweat glands often “pant”in warm weather. Panting is the rapid movement of air into and out of the upper respiratory passages, where the warm surfaces evaporate large amounts of water. In this way the animal may lose large amounts of heat. 排泄时，尿液和粪便的温度与人体体温一致，由此，排泄也引起少量的散热。When excreted, urine and feces are at body temperature, and their elimination results in a very small amount of heat loss

下丘脑负责对体温的调节，并且被认为是人体的―恒温器‖。作为恒温器，下丘脑通过平衡产热和散热使身体保持在设定的温度上来维护体温的―设置‖。The hypothalamus is responsible for the regulation of body temperature, and is considered the “thermostat”of the body. As the thermostat, the hypothalamus maintains the “setting”of body temperature by balancing heat production and heat loss to keep the body at the set temperature 为此，下丘脑必须接收到体内温度和环境温度信息。下丘脑区特定神经元会感知到流经大脑的血液温度变化。皮肤的温度感受器会提供人体所处的外在温度变化信息。接着，下丘脑将这感官信息整合，并加快必要的反应来使体温维持在正常范围内In order to do this,the hypothalamus must receive inforrmation about the temperature within the body and about the environmental temperature. Specialized neurons of the hypothalamus detect changes in the temperature of the blood that flows through the b r a i n .The temperature receptors in the skin provide information about the external temperature changes the body is exposed to. The hypothalamus then integrates this sensory information and promotes the necessary responses to maintain body temperature within the normal range. 皮肤温度感受器负责提供肌体接触到外部温度变化的信息，接着下丘脑将感官信息整合，为使体温维持在正常范围进行必要的反应。

Mechanisms to Increase Heat Loss在温暖的环境下或者运动时，人体体温易于上升，就需要更大量的散热。这一点可以通过皮肤的血管扩张和增加排汗来完成。血管扩张使更多的热血接近人体表层，热量随之释放到环境当中。然而，如果环境温度高于人体体温，这个机制就会没有效率。第二个机制是增加排汗，即：多余的体热将汗液蒸发到皮肤表面。就像前边提到的那样，当大气湿度高时，排汗效率低下。In a warm environment or during exercise, the body temperature tends to rise, and greater heat loss is needed. This is accomplished byvasodilation in the dermis and an increase in sweating. Vasodilation brings more warm blood close to the body surface, and heat is lost to the environment. However, if the environmental temperature is higher than

应激

身体一直在不断变化的条件下保持内环境恒定。例如，血液和体液中形成的过多酸和碱性物质，可以通过肾脏清除掉。尽管在极端气候下，仍可以保持正常的体温，身体会储存适量的水来防止组织脱水或水肿。这种恒定状态的维持就被称作稳态。体内功能的调节受到大脑的下丘脑控制，大脑的下丘脑控制着自主神经系统和主要的内分泌腺----垂体。下丘脑不仅控制着稳态，当身体或身体的一部分处于应激时，它能够感知到，且通过神经和腺体做出适当的反应。

稳态的维持和身体对应激的反应如何与疾病联系起来呢？身体不断地受到应激的影响，这就要求大大增加体内活动。在对应激做出反应或调整适应的过程中，疾病就会产生。考虑一下先前我们对炎症的描述。尽管它可能会产生严重的疼痛和红、肿、热、痛等这些典型的症状，但是炎症仍是身体积极的防御反应。它可以通过阻止和试图克服外来入侵物（如病原微生物或有毒物质）的方式来防止感染的扩散。

和炎症机制紧密相关的是过敏反应。在这种情况下，炎症反应对抗一种通常是无害的入侵物，如花粉、尘土或特定的食物。病人会患上花粉热、哮喘或荨麻疹。在这些疾病中，炎症弊大于利。一些疾病反应出身体对一种刺激物的不恰当反应。疾病远不止患病者克服它这么简单。它包括身体对疾病的对抗过程。呼吸系统的疾病（咳嗽和打喷嚏）是身体帮助清除喉咙和鼻子里的刺激物的反射活动。呕吐-----胃肠道疾病的一种症状----是缓解痛苦的一种反射活动。任何一种疾病的严重性很大程度上取决于病人对疾病的抵抗力。

应激对身体的影响

许多疾病与应激有关。胃肠道系统疾病、呼吸系统疾病和皮肤病如果不是由应激引起，通常

会由应激而加重。高血压是受应激影响非常大的另外一种疾病。

人生中有许多情况可能会引起应激，如居住条件、职业、受伤、饮食缺乏和长时间暴露于寒冷中。担忧、疲乏和酗酒也可以引起应激。由应激造成的伤害的体征通常是身体防御伤害或适应它的结果。

当身体受到像外伤这样的应激影响时，身体会发生什么变化呢？血糖水平升高，为受伤的组织修复提供更多的能量供应。受伤的部位会由于更多的血液流向受伤区域而出现炎症。嗜中性粒细胞数目增加，使吞噬细胞能够吞食外来物质和细胞碎片。

如果受伤严重导致血液丢失，病人就会休克。血液量减少，血压降低，静脉回流心脏的血液就会缺少。心输出量不足以满足身体的需要，病人就会因为没有足够的血液到达大脑而失去意识。

身体对这种应激的反应就是增加血压。特殊的神经受体感知到低血压，通过一种将要解释的神经机制来升高血压。由于血液丢失导致血压降低，肾脏能够感知到，释放一种被称作肾素的物质来辅助恢复正常的血压。肾上腺受到刺激释放肾上腺素，也可以升高血压，增强心脏的活动。

自主神经系统对应激反应时的功能

我们都熟悉我们的身体对应激情形、受惊吓或心烦意乱做出的反应。心脏会吓得嘣嘣地跳，血压升高，呼吸加快，出汗增加。这些变化通过自主神经系统活动为满足应激需要提供了更多的能量。

交感神经系统的大部分同时受到应激的刺激。第一反应就是把血液重新分配到最需要的地方：心脏、大脑和呼吸肌。这可以通过皮肤和胃肠道血管收缩和通向心脏、大脑和呼吸肌的血管舒张来完成。血管收缩升高血压，可以引起更多的静脉血回流至心脏增加心输出量。当受到交感神经系统的刺激时，肝脏会释放储存的葡萄糖到血液里，因此为活跃的新陈代谢细胞提供更多的能量源。随着甲状腺在应激条件下受到刺激分泌更多的甲状腺素，细胞的新陈代谢率也会增加。肾上腺髓质释放肾上腺素，可以增加交感神经系统的刺激作用。来自肾上腺皮层的糖皮质激素也可以增加血糖水平。身体对应激反应整个激活的状态就是我们所知的警戒反应。

应激与肾上腺皮质激素

警戒反应的信号被发送给下丘脑，下丘脑依次将释放因子发送给垂体。垂体分泌促肾上腺皮质激素和促甲状腺素，它们刺激甲状腺和肾上腺皮层释放甲状腺和皮质类固醇。

皮质醇（一种糖皮质激素）有抗炎作用，且可以抑制不必要的防御反应。在花粉热和类风湿关节炎中，炎症实际上是疾病。这类疾病中，没有要阻止的病原和毒素，炎症反应是有害的而不是有利的。

醛固酮和有抗炎作用的皮质醇保持适当平衡是很有必要的。在应激条件下产生过多有抗炎作用的激素会由于削弱了感染机体周围的屏障而引起感染扩散。在结核病扩散中应激成为诱因就是这个原因。直到有过多的皮质醇循环，结核杆菌都藏在隐凹里。通常寄生在呼吸道、肠道和皮肤的非致病性的微生物，当抵抗它们的防御机制削弱时就会变得危险。抗炎作用的皮质激素不仅可以抑制对抗微生物的免疫反应，还可以抑制移植手术过程中的排斥外来组织倾向。这些激素在防止典型炎症疾病中不必要的炎症反应，作用非常重要。皮质激素的治疗

皮质类固醇作为治疗许多炎症疾病的作用已经被证实。由于这些激素的副作用，要谨慎使用。大剂量或长时间使用皮质醇或皮质酮会降低病人对感染的反应，因此在缺少炎症症状时，感染会未被注意进而广泛扩散。

应激相关的疾病

受应激而加重的许多疾病的症状、原因和治疗，我们已经描述。这部分将解释应激或警戒反

应如何影响特定的疾病。受应激影响的胃肠道疾病

胃肠道系统尤其受应激影响，这种情况大部分人都经历过。心烦意乱、担忧或恐惧可以引起呕吐、腹泻或便秘。一些人在应激时会失去胃口，而另外一些会暴饮暴食。

消化性溃疡是应激相关的疾病的一个重要例子。溃疡病人通常精神紧张，易于担忧，非常谨慎。长时间的生理或心理应激会引起警戒反应和胃液分泌增加，胃液中富含消化酶和胃酸。还有些人胃或十二指肠粘膜的保护屏障，应激时受分泌的皮质激素影响被削弱。治疗包括确定应激源或焦虑，并且要让病人有规律进食或使用药物治疗。一些溃疡被称作应激性溃疡，在休克之后或创伤之后，如严重的烧伤或外伤，突然形成。这些溃疡有别于慢性溃疡，通常表现为流血而非疼痛。

溃疡性结肠炎（结肠的炎症和溃疡）是不明原因可以由应激而加重的疾病。这种疾病伴随带血和粘液的腹泻。炎症的治疗包括非刺激性的食物，抗生素来防止伤口感染，另外要多休息。病人要远离情感的应激，提供其心理咨询来帮助解决焦虑和紧张。因为皮质类固醇的抗炎作用通常要开出这种药物。

局部性肠炎或Crohn疾病与溃疡性结肠炎相似。它不是由病原微生物引起但是可以由应激而加重，比如心烦意乱。局部性肠炎是大肠或小肠的炎症。病人会经历腹痛、腹泻和体重减轻。皮质类固醇要谨慎使用防止过量产生副作用。偏头痛综合征

偏头痛患者知道这种疾病比周期性头痛影响更严重。偏头痛通常始于一侧太阳穴，传至另外一侧，然后就无特征了。它会持续一小段时间或几天，严重程度也非常广泛。胃肠道疾病经常伴随着头痛，包括恶心、呕吐、腹泻和便秘。

一些症状通常先于头痛发作：视觉变化如眼前跳动光，眩晕，胳膊和腿麻木，皮肤泛红或白。在头痛发作疼痛。眼睛会红、肿，表现出多泪。

治疗旨在收缩舒张的血管，更新更为有效的药物正在成为可能。如果头痛不严重，阿司匹林在缓解头痛方面很有效，但也需要其它药物。这些收缩血管的药物的剂量必须认真控制防止其副作用。

受偏头痛影响的人通常是努力工作的和喜欢有规律的人。恐吓或冲突会引起他们紧张和疲乏。通常，应激先于头痛发作。偏头痛通常发生在女性月经期。有时候，头痛发作也会由高海拔；天气变化；食用巧克力，奶酪；吸烟和饮酒引起。

应激或警戒反应会引起体液广泛积聚。这可能由于受刺激的肾上腺，醛固酮分泌增加导致。醛固酮引起钠和水潴留，过多的体液潴留引起血管变化进而引起头痛。头痛发作前，一些神经递质物质水平也会出现异常，如血清素。

头痛患者应该帮助其识别出引起头痛的应激源。心理咨询可以使患者表达内心的气愤、抑郁或矛盾，进而帮助他们更好地解决。

和偏头痛紧密相关的是丛集性头痛，因为它有丛集性发作的倾向而命名，通常一天发作几次，或发作好长时间。这些剧烈的跳动性疼痛通常限定于一侧，且持续几个小时。男性比女性更容易受丛集性头痛影响，女性容易患偏头痛。治疗与偏头痛相似。心血管系统与应激

交感神经系统对应激的反应是收缩外周的血管，升高血压。肾上腺皮层对应激的反应也是通过分泌过量的醛固酮引起血压升高。钠和水在醛固酮影响下会潴留，增加的体液引起血压升高。一位有高血压倾向且长时间受应激影响的人很可能会患慢性高血压。通常伴随动脉硬化，加重心脏负担。在这些情况下，心脏病发作风险增加，尤其如果人肥胖，吸烟和久坐。高血压的一个特殊例子，怀孕时的子痫，这种疾病，病人的血压会突然急剧升高。子痫通常发生在第九个月，伴随着血清白蛋白水平增加，出现在尿液里。痉挛会导致昏迷。子痫的原因不清楚，但可以由应激而加重。呼吸系统与应激

当一个人由于应激抵抗力下降时，呼吸系统通常会受到疾病的影响。应激的原因可能是情感的因素，如担忧、抑郁、矛盾或身体的因素，如受伤、长期暴露于寒冷或营养不良。应激会

降低身体对感染的抵抗力，正如前面在肺结核中提到的。

应激时患上普通感冒大部分人都经历过。警戒反应时皮质激素的释放可能与这种现象有关。呼吸系统的感染性疾病并不是由应激引起的唯一疾病。哮喘通常有过敏的基础，这种疾病表现出支气管直径明显变化和气道阻塞。各种过敏源和刺激物都可以引起哮喘发作。抗原---抗体复合体与支气管肥大细胞表面结合，引起组胺和其它致痉物释放，这些物质会引起支气管肌肉组织的痉挛性收缩。

哮喘发作（咳嗽、呼吸困难和气短）会由情感或心理压力而加重。哮喘病人通过对自主神经活动过度反应，表现出支气管活动多度。

其它加重哮喘的因素有过度劳累和病毒性呼吸道感染。儿童的哮喘表现出开学时由于各种原因而加重。一种新的经历在情感上就是有压力的，学校环境增加了儿童接触呼吸道感染的机会，学校活动也会使儿童过度劳累。

哮喘的治疗始于在可能的地方减少接触过敏原或刺激物。旨在脱敏的过敏针对于一些人是有帮助的。使用像肾上腺素这样的支气管扩张药通常十分有效。严重的病例可能需要使用皮质类固醇或促肾上腺皮质激素来降低炎症反应、浮肿和过多粘液产生。受应激影响的皮肤病皮肤病可能由感染源、过敏或异常细胞活动引起，但许多都受应激影响。感冒疮或热性疱疹，属于病毒性感染，通常发生于对感染的抵抗力下降时。病毒可能存在且无症状很长时间，只有在情感或身体出现应激时才有感染的活性。之前颅内动脉会发生血管收缩这样的变化，紧跟着血管舒张，引起跳动性荨麻疹是一种过敏性皮肤病，可以由应激而加重。过敏与应激的关系已经讨论过。荨麻疹的治疗包括使用皮质类固醇来降低炎症反应。湿疹是另外一种受情感应激影响的过敏性炎症性皮肤病。

牛皮癣的病因还不清楚，但是它有遗传的基础，且可以由应激加重。使用皮质类固醇和其它药物在控制伤口上十分有效。

应激造成的身体系统变化

各种应激有关的疾病或适应性疾病我们已经讨论：心血管系统疾病；呼吸系统疾病；胃肠道系统疾病；过敏和偏头痛综合征。实验已表明长时间应激导致的其它明显变化。肾上腺皮层会由于过度刺激产生激素而肥大。淋巴样组织，对于免疫反应和清除外来入侵物方面很重要，会萎缩。胃和十二指肠粘膜发生。