医学专业英语翻译及答案

Chapter 1

Passage 1 Human Body

In this passage you will learn:

1. Classification of organ systems

2. Structure and function of each organ system

3. Associated medical terms

To understand the human body it is necessary to understand how its parts are put together and how they function. The study of the body's structure is called anatomy; the study of the body's function is known as physiology. Other studies of human body include biology, cytology, embryology, histology, endocrinology, hematology, immunology, psychology etc.

了解人体各部分的组成及其功能，对于认识人体是必需的。研究人体结构的科学叫解剖学；研究人体功能的科学叫生理学。其他研究人体的科学包括生物学、细胞学、胚胎学、组织学、内分泌学、血液学、遗传学、免疫学、心理学等等。

Anatomists find it useful to divide the human body into ten systems, that is, the skeletal system, the muscular system, the circulatory system, the respiratory system, the digestive system, the urinary system, the endocrine system, the nervous system, the reproductive system and the skin. The principal parts of each of these systems are described in this article.

解剖学家发现把整个人体分成骨骼、肌肉、循环、呼吸、消化、泌尿、内分泌、

神经、生殖系统以及感觉器官的做法是很有帮助的。本文描绘并阐述了各系统的主要部分。

The skeletal system is made of bones, joints between bones, and cartilage. Its function is to provide support and protection for the soft tissues and the organs of the body and to provide points of attachment for the muscles that move the body. There are 206 bones in the human skeleton. They have various shapes - long, short, cube - shaped, flat, and irregular. Many of the long bones have an interior space that is filled with bone marrow, where blood cells are made.

骨骼系统由骨、关节以及软骨组成。它对软组织及人体器官起到支持和保护作用，并牵动骨胳肌，引起各种运动。人体有206根骨头。骨形态不一，有长的、短、立方的、扁的及不规则的。许多长骨里有一个内层间隙，里面充填着骨髓，这即是血细胞的制造场所。

A joint is where bones are joined together. The connection can be so close that no movement is possible, as is the case in the skull. Other kinds of joints permit movement: either back and forth in one plane - as with the hinge joint of the elbow - or movement around a single axis - as with the pivot joint that permits the head to rotate. A wide range of movement is possible when the ball - shaped end of one bone fits into a socket at the end of another bone, as they do in the shoulder and hip joints.

关节把骨与骨连接起来。颅骨不能运动，是由于骨与骨之间的连接太紧密。但

其它的关节可允许活动，如一个平面上的前后屈伸运动，如肘关节；或是绕轴心旋转运动，如枢轴点允许头部转动。如果一根骨的球形末端插入另一根骨的臼槽里，大辐度的运动（如肩关节、髋关节）即成为可能。

Cartilage is a more flexible material than bone. It serves as a protective, cushioning layer where bones come together. It also connects the ribs to the breastbone and provides a structural base for the nose and the external ear. An infant's skeleton is made of cartilage that is gradually replaced by bone as the infant grows into an adult.

软骨是一种比一般骨更具韧性的物质。它是骨连结的保护、缓冲层。它把肋骨与胸骨连结起来，也是鼻腔与内耳的结构基础。一个婴儿的骨骼就是由软骨组成，然后不断生长、骨化，使婴儿长大成人。

The muscular system allows the body to move, and its contractions produce heat, which helps maintain a constant body temperature. Striated muscles can be consciously controlled. The ends of these muscles are attached to different bones by connective tissue bands so that when the muscle contracts, one bone moves in relation to the other. This makes it possible to move the whole body, as when walking, or to move just one part of the body, as when bending a finger. Contractions of the heart and smooth muscles are not under conscious control. Smooth muscles are found in the walls of organs such as the stomach and the intestines and serve to move the contents of these organs through the body.肌肉系统使躯体运动，肌肉收缩产生的热有助于维持一个恒定的

体温。人体能够有意识地控制条纹肌。结缔组织使肌肉末端附着于不同的骨面上，所以当肌肉收缩时，两骨彼此靠近而产生运动。这也就使整个人体可以运动起来，如走路，运动躯体某个部位，如弯曲手指。心脏收缩和平滑肌收缩就不是被意识所控制的。器官壁内层的平滑肌，如胃肠壁的平滑肌把胃肠中的物质运送到全身。

The circulatory system. All parts of the body must have nourishment and oxygen in order to function and grow, and their waste products must be removed before they accumulate and poison the body. The circulatory system distributes needed materials and removes unneeded ones. It is made up of the heart, blood vessels, and blood, which together make up the cardiovascular system. The blood is also part of the body's defense system. It has antibodies and white blood cells that protect the body against foreign invaders. 循环系统：机体的所有部分需要营养物质和氧气来使之发挥功能和生长，也需要在这些器官所产生的废物积聚而危害生命之前将其排除。循环系统运送有用物质，排泄废物。心血管系统是循环系统的组成之一；心血管系统包括心脏、血管及血液。血液也是机体防御系统的一个部分，血液中有抗体及白细胞来防止机体受到外来的侵袭。

The heart is a muscle that is divided into two nearly identical halves: one half receives blood from the lungs and sends it to the rest of the body, the other half sends blood that has traveled through the body back to the lungs. When the heart muscle contracts, the blood is forced out into arteries and enters small capillaries. Blood returns to the heart through veins. 心

脏是一块被分为几乎对等两半的肌肉。一半吸收来自肺部的血液，并将血液运送到机体的其余部位，另一半使流经全身的血液回流人肺。心脏收缩时，动脉把全身血液输送到毛细血管。静脉输送血液返回心脏。

Also functioning in circulation is the lymphatic system. Some of the fluid that surrounds cells does not reenter the blood vessels directly. This fluid, called lymph, returns to the heart by way of another system of channels - the lymph vessels. Lymph nodes along these vessels filter the fluid before it reenters the blood. The spleen is a large lymphatic organ that filters the blood. 淋巴系统也是循环系统的一个组成部分。一些细胞周围的体液不是直接回流入血管通道，这种体液叫淋巴液，它是流经另一个管道系统——淋巴管而回流人心脏。沿淋巴管的淋巴结将淋巴液过滤，过滤后再回流人血液。脾是一个过滤血液的大淋巴器官。

The respiratory system takes in oxygen from the air and expels carbon dioxide and water vapor. Air enters the nose and mouth and travels through the larynx, and trachea. The trachea divides to enter each of the two lungs and then divides more than 20 times to form a very large number of small air spaces. Oxygen from the air enters the blood through capillaries in the walls of these air spaces, and the blood release carbon dioxide into the air spaces to be exhaled. 呼吸系统从空气中摄取氧气，并将二氧化碳、水蒸气排出体外。空气经鼻腔、口腔人喉管、气管。气管分成左右支气管，各连结左右肺，左右支气管再分枝20多次，在终端形成大量微小的肺泡。从空气摄取的氧气流经这些肺泡壁内

的毛细血管流入血液，血液再经肺泡把释放出的二氧化碳排出体外。

The digestive system consists of a tube extending from the mouth to the anus. In it, food and fluids are taken in, moved through the body, and broken down into small molecules that are absorbed into the circulatory system. This breakdown, known as digestion, is both a mechanical and a chemical process.消化系统是一个从口腔直到肛门的管道。食物和液体在消化道里被吸收，在肠道里移动时，被分解成小分子物质后再进入循环系统。这种分解，即消化，是一个机械过程，也是一个化学过程。

Food enters through the mouth, where chewing and saliva start to break it up and make it easier to swallow. Next, the food travels down through the esophagus to the stomach. Contractions of the stomach's muscular wall continue to break down the food mechanically, and chemical digestion continues when acid and enzymes are secreted into the stomach cavity. 食物进入口腔里，咀嚼和唾液开始将食物粉碎，使之便于吞咽。接着，食物经食管人胃。胃肌壁的收缩继续机械化地分解食物，而当酸和酶分泌入胃腔时，化学性消化开始。

The liquified food gradually passes into the small intestine. In the first part of the small intestine, called the duodenum, enzymes from the pancreas are added. These enzymes complete the chemical breakdown of the food. The digestion of fat is aided by bile, which is made in the liver and stored in the gall bladder. The small intestine of an adult is about 21 feet (6.4

meters) long. Most of its length is devoted to absorbing the nutrients released during these digestive activities. 液体化食物逐渐进入小肠。小肠的起始部分叫十二指肠，胰腺分泌的酶辅助食物消化。这些酶完成食物的化学分解。肝脏分泌的胆汁贮存在胆囊内，胆汁有助于脂肪消化。一个成年人的小肠有21英尺（6.4米）长。小肠的大部分肠段用来吸收消化过程中释放的营养物质。

The liquid remainder of the food enters the large intestine, or colon, which is about 12 feet (3.7 meters) long. It is more than twice as wide as the small intestine. In the large intestine most of the fluid is absorbed, and the relatively dry residues are expelled. 液状的剩余食物进入大肠，或结肠，它大约有12英尺（3.7米）长。大肠是小肠的两倍多宽。大部分液体在大肠内被吸收，相对干化的残余物被排出体外。

The urinary system maintains normal levels of water and of certain small molecules such as sodium and potassium in the body. It does this by passing blood through the kidneys, two efficient filtering organs that get rid of any excess of various molecules and conserve those molecules that are in short supply. 泌尿系统维持水分及体内某些小分子物质，如钠、钾的正常水平。身体是通过让’肾过滤血液来做到这一点的。肾是两个有效的过滤器官，它滤出各种多余的小分子物质，保留那些供应不足的小分子物质。

The fluid that leaves the kidneys, known as urine, travels through a tube called the ureter to the bladder. The bladder holds the urine until it is voided from the body through another tube, the urethra. 从肾流出的液体，

即尿，通过输尿管人膀胱。膀胱起贮存尿液的作用，直到尿经膀胱另一端的管道排出。

The endocrine system. The two systems that control body activities are the endocrine system and the nervous system. The former exerts its control by means of chemical messengers called hormones. Hormones are produced by a variety of endocrine glands, which release the hormones directly into the blood stream. 内分泌系统。内分泌和神经是调控机体活动的两个系统，前者依靠其化学信使——激素发挥作用。激素是由各种内分泌腺体制造，并直接被释放入血流

A major gland is the pituitary, which is located under the brain in the middle of the head. It produces at least eight hormones, which affect growth, kidney function, and development of the sex organs. Because some of the pituitary's hormones stimulate other glands to produce their own hormones, the pituitary called the master gland. 脑垂体是一个主要腺体，它位于头中部脑下方。它至少分泌八种激素，这些激素对人体生长、肝功能及性器官发育有影响。因为脑垂体分泌的一些激素促进其他腺体分泌激素，所以脑垂体是主要腺体。

Another gland, the thyroid, is located between the collar bones. Its hormone controls the rate of the body's metabolism. The sex organs (ovaries end testes) make the sex cells and also make hormones that control certain characteristics of males and females. Located on top of each kidney is the adrenal gland, which produces cortisone and adrenaline. The pancreas

produces not only digestive enzymes but also 3 insulin and glucagon, which control the body's use of sugar and starches. 另一个腺体，甲状腺，位于锁骨之间。甲状腺激素调控着机体新陈代谢的速度。性器官（卵巢、睾丸）分泌性细胞和性激素，这些激素控制着男性和女性的某些特征。每边肾上方是肾上腺，它分泌可的松和肾上腺激素。胰腺不仅分泌消化酶，而且分泌胰岛素和高血糖素，这两种激素控制机体的糖分及淀粉的消耗。

The nervous system. The brain, the spinal cord and the nerve - also controls body activities. The lower parts of the brain control basic functions such as breathing and heart rate as well as body temperature, hunger, and thirst. Above these regions are the centers for sight, sound, touch, smell, and taste, and the regions that direct voluntary muscular activities of the arms and legs. Performed here are the higher functions of integrating and processing information. 神经系统——脑、脊髓及神经，也调控机体活动。脑的偏下部位控制着诸如呼吸、心跳、体温、饥渴的基本活动。而脑的偏上部位则是视觉、听觉、触觉、嗅觉及味觉中心，也是指挥臂、腿随意肌肉运动的区域。神经系统更高级的功能是整合、处理信息。

The brain receives and sends information by means of nerves, many of which lie partly in the spinal cord. The spinal cord is protected by the spinal column. Nerves enter and leave the spinal cord at each level of the body, traveling to and from the arms, legs, and trunk. These nerves bring information from the various sense organs. The information is processed by

the brain, and then messages are carried back to muscles and glands through out the body. 脑通过神经收集并传送信息，许多神经部分地分布在脊髓里。脊髓由脊柱保护。在机体每一级，神经传人、传出脊髓，往返于臂、腿、躯体。这些神经输送来自各种感觉器官的信息。信息经脑处理后输送回全身及腺体The reproductive system is constructed differently for males and females. The male reproductive system is responsible for producing, transporting and maintaining viable sperm (the male sex cell). It also produces the male sex hormone, testosterone, which regulates the development of a beard, pubic hair, a deep voice and other bodily characteristics of the adult male. 男、女性的生殖系统不同。男性生殖系统产生、输送、维持能存活的精子（男性性细胞）。它也分泌男性激素、睾酮，以此调节胡须、阴毛、深沉嗓音极其他成年男子身体发育的特征。

The female productive system is responsible for producing and transporting ova (the female sex cells), eliminating ova from the body when they are not fertilized by sperm, nourishing and providing a place for growth of an embryo when an ovum is fertilized by sperm, and nourishing a newborn child. The female reproductive system also produces the female sex hormones, estrogen and progesterone, which regulate the development of breasts and other bodily characteristics of the mature female. 女性生殖系统产生、输送卵子（女性性细胞），将未受精的卵子排出体外，而当精、卵结合时，女性生殖系统培养、提供胚胎生长场所，并孕育新生儿。女性生殖系统也分泌女性性激素——雌

激素和孕酮，以此调节乳房及其他成熟女性身体发育的特征。

The skin is a complete layer that protects the inner structures of the body, and it is the largest of the body's organs. It keeps out foreign substances and prevents excessive water evaporation. The nerves in the skin provide tactile information. The skin also helps keep the body's temperature close to 37 °C, heat is conserved by reducing blood flow through the skin or is expended by increasing blood flow and by evaporation of sweat from the skin. Hair and nails are accessory structures of the skin. 皮肤是保护肌体内层结构的完整层，也是机体的最大器官。皮肤防御外来侵袭，防止过多水分蒸发。皮肤上的神经提供触觉信息。皮肤也能将体温维持到98.6华氏度（约37摄氏度）。通过皮肤的血流量降低时，热量就被储存起来，通过皮肤的血流增加及汗液蒸发时，热量就散发。头发及指甲是皮肤的附属结构。

Cells and Tissues细胞与组织

In this passage, you will learn:1.Human body systems as a whole 2.Vital parts of a cell 3.Four kinds of tissues

Cells are organized into tissues, and tissues are arranged into organs, which in turn are grouped into systems. Each body system serves its specific functions. Bear in mind however that the body functions as a whole----no system is independent of the others. They work together to maintain the body’s state of internal stability, terme d homeostasis. Now let’s begin our discussion with cells, the smallest unit of living matter that can exist

by itself. 细胞构成组织，组织构成器官，器官又进一步构成系统。人体的每个系统都有其特定功能，但是，请记住这里:机体是作为一个整体来发挥作用的，没有哪个系统能够独立于其他系统而存在，是整体系统共同作用保持了机体内部的稳定状态，即体内平衡。现在，我们先讨论细胞─能独立存在活性物质的最小单位。

The body can be studied from its simplest to its most complex level, beginning with the cell. All body functions result from the activities of billions of the specialized cells. Some plants and animals consist of only a single cell. Others are composed of many billions of cells. 从细胞开始，我们能够从最简单到最复杂的水平来研究机体。所有人体的功能都来自亿万个特定细胞活动，有的动植物仅由一个细胞构成，其他生物则由亿万个细胞构成。

Cells exist in a variety of shapes and sizes. They may, for example, be cube-shaped or flat. Scientists who study cells have determined that a single cell may be as large as a tennis ball or so small that thousands would fit on the point of a needle. The yolk of a hen’s egg is actually a very large cell. By contrast, bacteria----each one of which is a tiny cell----are among the smallest cells. Regardless of its shape or size, every cell contains the “machinery” needed to maintain life. While normally cells function with great efficiency, they are subject to various disorders that result in disease. 细胞有很多种形状和大小。列如：有可能是立方形或扁形的。科学家的研究发现单独一个细胞可以像网球一样的大小，或小到几千个细胞才能刚好填满针头。鸡的蛋黄是一个非常大的单细胞。微小的细菌呢算是最小的细胞。不管是细胞大小

或形状的不同，每个细胞都有“需要存活的机制”。对每个正常的细胞，有效力的细胞，都存在许多问题，能导致疾病。

The size of cells is usually measured in microns. A micron is a millionth of a meter, and about 25,000 microns equal one inch. The smallest bacteria are about 0.2 micron in diameter. The average cell in the human body----about ten microns in diameter----is a speck barely visible without the aid of a microscope. 细胞的大小是以“微米”为长度单位。微米是一米的一百万分之一，25000微米等于一寸。最小的细菌的圆径是0.2微米。人体正常细胞的评价圆径约十微米，肉眼勉强可以看得到，不需要显微镜的帮助。

The study of cells is the branch of biology called cytology. The science that deals with cells on the smallest structural and functional level is called molecular biology. 研究关于“细胞”是生物学的分支，成为细胞生物学。在最微小水平针对细胞的结构及功能的研究成为分子生物学。

All cells consist of protoplasm, the “living jelly.” The protoplasm of a typical cell forms three vital parts----the cell membrane, the cytoplasm, and the nucleus. The membrane encloses the other cell structures. Much of the chemical work of the cell is done in the cytoplasm, which surrounds the nucleus. The nucleus, enclosed by its own membrane, is the control center of the cell. (see Figure 1-1) 所有细胞都是以“原生质”，又称“生命胶质”所形成的。典型细胞的原生质形成了三个重要部分，细胞膜、细胞质和细胞核。细胞膜圈住了细胞的其他结构。大部分的化学反应都在细胞核周围，细胞质完成的。

被自己的膜包围的细胞核是细胞的控制中心。

the cells Membrane细胞膜

Cells can survive only in a liquid medium that brings in food and carries away waste. For one-celled organisms this fluid is an external body of water----the ocean, a lake, or a stream. For many-celled plants and animals, however, the medium is part of the organism----in plants, the sap; in animals, the blood. 细胞只能存活在能供养分又能排除废物的液体媒介中。对单细胞生物来说，这就是细胞外的液体，如：大海里、河里或水流中。在对多细胞生物而言，这种媒介就是生物体的一部分，植物以汁液的形式，动物以血液的形式。

The cell membrane is semipermeable, or differentially permeable----some substances can pass through it, but others cannot. This characteristic enables the cell to admit useful substances and to reject harmful substances from the surrounding fluid as well as to force out, or excrete waste products into the fluid. 细胞膜是半渗透性或区别性的渗透膜，即某些物质能渗透。这个特殊性使细胞对细胞周围只吸收了需要的物质而排除掉有害的物质，包括细胞内的废物通过液体化后排出细胞外。

The cell membrane is an extremely thin but tough band of protein and phospholipid molecules. Phospholipids are chemicals similar to stored fat. On the evidence of electron micrographs, biologists believe that it has pores through which certain small molecules pass intact. Substances probably pass through the cell membrane in several ways. Small chambers located on the cell

membrane called caveolae gather chemical signals and channel them into the cells. The caveolae may also help distribute proteins throughout the cell. Large molecules enter the cell by a process called diffusion, in which they may be dissolved by substances in the cell membrane. They can then through the membrane without difficulty. Some cells take in large molecules by means of pinocytosis. In this process, the cell membrane forms a pocket around large molecules floating against it. The molecule-and-fluid-filled pocket then breads loose from the membrane to become a bubblelike vacuole, and the vacuole then drifts into the cytoplasm. Finally, the vacuole wall breaks up and the molecules are released into the cytoplasm. 细胞膜是一种非常薄但确以很坚固的蛋白磷脂膜形成。磷脂是一种类似于储存的脂肪的蛋白物质。通过电子显微镜，生物学家相信细胞膜有孔，使较小的物质完全可以通过。物质可通过多种方式从细胞膜进入。细胞膜上的结构，称“小穴”，可接受化学信号再传到细胞内。小穴还可能参于细胞蛋白的分配。大的分子可通过“渗滤”进入细胞内，或被细胞膜内体分解，使它们更容易的进入细胞内。有些细胞可通过“胞饮”方式吞饮较大的物质。这个过程是通过细胞膜在大物质形成了“带”把它包围着，将它以泡状的“液泡”引入细胞质，最后包围解散，大物质成功的进入细胞内。

The cytoplasm细胞质

The cytoplasm is mainly water. Its water content varies from a minimum of about 65 percent to a maximum of about 95 percent. The solids in the cytoplasm include granular proteins, carbohydrates, droplets of fat, and

pigments. The cytoplasm is thus a colloidal system. 细胞质主要成分是“水”。水分含量有百分之65到最高，百分之95。细胞质内的固体包括蛋白颗粒、碳水化合物、脂肪小滴和色素。细胞质是胶体性的。

The cytoplasm may be either watery or syrupy, depending on the concentration of solids dispersed in the fluid. When the solid content decreases, these structures seem to vanish. Changes in concentration also produce an apparent steaming of the cytoplasm from place to place within the cell. This occurs, for example, when food molecules enter the cell. 细胞质可能是水性或糖浆性，根据散在细胞质内固体的浓度。当固体成分浓度增多，膜状和纤维状结果在细胞质显出。而当固体成分浓度减少时，膜状和纤维状的结构就消失。浓度的变化还可以表现细胞质内局部流动的变化。食物分子进入时可见。

Most of the cell’s constant work of keeping alive is performed in the cytoplasm. Here food molecules are changed into the material needed for energy and materials for growth or stiffening of the cell membrane are manufactures needed by the rest of the organism. For example, plant cells containing chlorophyll manufacture glucose----a plant food----from carbon dioxide and water. 大部分为了细胞存活的工作都在此处（细胞质）完成的。在此处，食物物质将被转化成提供细胞能量的材料和提供细胞生长的材料，或细胞膜的增强剂所生产。多细胞植物的细胞质还是生产了对其他生物提供食物的物质。列如：植物叶绿素所产生的葡萄糖，植物的食物，从水和二氧化碳合成。

One of the cytoplasm’s key energy transactions occurs in the

sausage-shaped mitochondria. Each mitochondrion has an inner and an outer membrane. Like the cell membrane, the membranes of the mitochondrion are semipermeable. Food molecules that pass into the cytoplasm are taken into the mitochondria and oxidized, or burned, for energy. 细胞质能量转换的要点发生在锥状形的线粒体。每个线粒体都有内膜和外膜。像细胞膜一样，线粒体的膜也是半渗透性。进入线粒体的食物分子被氧化提供出能量。

The endoplasmic reticulum, a network of membranous tubes, runs through the cytoplasm. In the opinion of some biologists, this network is a continuous structure that begins at the cell membrane, twists through the cytoplasm, and ends at the membrane surrounding the nucleus. Located along the endoplasmic reticulum as well as elsewhere in the cytoplasm are numerous ribosomes. These tiny granules consist in part of ribonucleic acid (RNA). Proteins are manufactured at the ribosomes. The Golgi complex, or Golgi apparatus, is a membranous structure composed of stacks of thin sacs. Newly made proteins move from the endoplasmic reticulum to the Golgi complex, where they are stored for later secretion. 胞浆网，在细胞质中由膜所形成管状的网。有些生物学家认为这是一种连续性结构，始点为细胞膜，在细胞膜内扭绞，终点为细胞核的膜。分布于胞浆网包括细胞质中某处的是核糖体。这些小颗粒是核糖核酸所形成的。蛋白质是在核糖体合成的。高尔基体是膜状囊包堆成层形成的。新合成的蛋白从胞浆网移动到高尔基体储存，为了后来分泌所用。

Vacuoles drift through the cytoplasm and usually carry food molecules

in solution. Lysosomes are structures somewhat similar in appearance to vacuoles but denser. They appear to have a digestive function. Each lysosome is filled with digestive enzymes and encased in a membrane. Lysosomes are believed to break down food substances brought into the cell by pinocytosis. It has been suggested that the Golgi complex plays a part in the formation of lysosomes. 在细胞质内游动的液泡一般是带着食物分子的溶液。溶酶体是一种有点像液泡的结构，但较稠。它是用来消化的。每个溶酶体的膜内都是添装着消化酶。我们认为它是消化通过“胞饮”方式的大物质。也认为高尔基体对溶酶体的形成有关系。

The Nucleus细胞核

Near the center of the cell is a roundish or oval-shaped nucleus. The nucleus controls the growth and division of the cell. It also contains the structures that transmit hereditary traits. 细胞的中央，圆形或椭圆形的就是细胞核。细胞核控制细胞的生长和分化。也装着遗传信息。

Enclosed by a two-layered membrane, the nucleus contains a liquid called nucleoplasm as well as strands of deoxyribonucleic acid (DNA) covered with a coating of protein. A strand of DNA consists of a long series of genes, which are the units of heredity of plants and animals. Genes determine the characteristics of a cell. They do this by regulating the production of RNA, which in turn controls the manufacture of specific proteins. 被两层膜圈住着，细胞核内含有称为“核质（浆）”的液体和脱氧核糖核酸的蛋白层。脱氧核糖

核酸缕是很长的基因系列所组成的，它是植物和动物的遗传信息。基因决定了细胞的特征。它是通过调节核糖核酸，使核糖核酸产出特异的蛋白。

Human cells, for example, make only proteins unique to human beings DNA strands are usually too thinly strung out to be seen with an optical microscope. Because the strands are readily stained with dyes, they are called chromatin. When a cell begins to divide, however, the chromatin thickens into the form of chromosomes. 列如：人的细胞，只产出人独特拥有的蛋白。脱氧核糖核酸缕一般都很细小过光学显微镜能观察到。因为脱氧核糖核酸缕能够染色后部分被染，称“染色质”。细胞分化过程中，染色体拾起变厚形成了“染色体”。

A nucleus not undergoing division has at least one nucleolus. The nucleolus contains a concentration of RNA. Biologists think RNA is made initially in the nucleus accordin g to a DNA “blueprint” and stored there until needed for protein manufacture. 细胞核分化核仁不会减少，最少要有一个核仁。核仁含有丰富的核糖核酸。生物学家认为核糖核酸原本在核仁里，根据脱氧核糖核酸的蓝图造出而藏在此处直到有蛋白合成的需要。

the nucleus of animal cells is a spherical structure called the centrosome, from which asters radiate. The centrosome contains a pair of rodded structure called centrioles, which usually lie at right angles to each other. Although centrioles and centrosomes have not been seen in plant cells, biologists believe that plant cells contain similar structures. 靠近动物

的细胞核的圆形结构叫“中心体”，可见呈放射状散发的星体。中心体内含有一对棍状结构，称为“中心粒”，一般都形成正确固定的角度。无法在植物细胞发现中心体和中心粒，但生物学家认为植物应该有存在类似功能的其他结构。

Tissues组织

Cells are organized into tissues that perform specific functions. The four basic tissue types are as follows: 多细胞组成了组织，为了特异的功能。四种基本的组织：

Epithelial tissues----covers and protects body structures and lines organs, vessels, and cavities. 上皮组织 : 覆盖及保护着身体结构和分清器官、导管和空腔。

Connective tissues----supports and binds body structures. It contains fibers and other nonliving material between the cells; included are fat tissues, cartilage, bone and blood. 结缔组织 : 支柱和联结着身体结构。包括细胞之间的纤维和其它无生物结构。包括脂肪组织、软骨、骨头和血液。

Muscle tissues----contracts to produce movement. The three types are：skeletal or voluntary muscle that moves the skeleton; the cardiac muscle of the heart; and the smooth muscle that forms the walls of the abdominal organs. Cardiac and smooth muscle can function without conscious control and are thus described as involuntary muscle. 肌肉组织 : 通过收拾来产生动作。分为三种：骨骼肌，作用于一般骨骼移动。心机，心脏的肌肉。平滑肌，形成胃肠道壁的肌肉。