【文章內(nèi)容簡(jiǎn)介】 eeps out foreign substances and prevents excessive water evaporation. The nerves in the skin provide tactile information. The skin also helps keep the body39。s temperature close to 37 176。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. 皮膚是保護(hù)肌體內(nèi)層結(jié)構(gòu)的完整層，也是機(jī)體的最大器官。皮膚防御外來(lái)侵襲，防止過(guò)多水分蒸發(fā)。皮膚上的神經(jīng)提供觸覺(jué)信息。（約37攝氏度）。通過(guò)皮膚的血流量降低時(shí)，熱量就被儲(chǔ)存起來(lái)，通過(guò)皮膚的血流增加及汗液蒸發(fā)時(shí)，熱量就散發(fā)。頭發(fā)及指甲是皮膚的附屬結(jié)構(gòu)。 Cells and Tissues細(xì)胞與組織In this passage, you will learn: body systems as a whole parts of a cell kinds of tissuesCells 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 wholeno system is independent of the others. They work together to maintain the body’s state of internal stability, termed homeostasis. Now let’s begin our discussion with cells, the smallest unit of living matter that can exist by itself. 細(xì)胞構(gòu)成組織，組織構(gòu)成器官，器官又進(jìn)一步構(gòu)成系統(tǒng)。人體的每個(gè)系統(tǒng)都有其特定功能，但是，請(qǐng)記住這里:機(jī)體是作為一個(gè)整體來(lái)發(fā)揮作用的，沒(méi)有哪個(gè)系統(tǒng)能夠獨(dú)立于其他系統(tǒng)而存在，是整體系統(tǒng)共同作用保持了機(jī)體內(nèi)部的穩(wěn)定狀態(tài)，即體內(nèi)平衡?，F(xiàn)在，我們先討論細(xì)胞─能獨(dú)立存在活性物質(zhì)的最小單位。 The body can be studied from its simplest to its most plex 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 posed of many billions of cells. 從細(xì)胞開(kāi)始，我們能夠從最簡(jiǎn)單到最復(fù)雜的水平來(lái)研究機(jī)體。所有人體的功能都來(lái)自億萬(wàn)個(gè)特定細(xì)胞活動(dòng)，有的動(dòng)植物僅由一個(gè)細(xì)胞構(gòu)成，其他生物則由億萬(wàn)個(gè)細(xì)胞構(gòu)成。Cells exist in a variety of shapes and sizes. They may, for example, be cubeshaped 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, bacteriaeach one of which is a tiny cellare 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. 細(xì)胞有很多種形狀和大小。列如：有可能是立方形或扁形的?？茖W(xué)家的研究發(fā)現(xiàn)單獨(dú)一個(gè)細(xì)胞可以像網(wǎng)球一樣的大小，或小到幾千個(gè)細(xì)胞才能剛好填滿針頭。雞的蛋黃是一個(gè)非常大的單細(xì)胞。微小的細(xì)菌呢算是最小的細(xì)胞。不管是細(xì)胞大小或形狀的不同，每個(gè)細(xì)胞都有“需要存活的機(jī)制”。對(duì)每個(gè)正常的細(xì)胞，有效力的細(xì)胞，都存在許多問(wèn)題，能導(dǎo)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 micron in diameter. The average cell in the human bodyabout ten microns in diameteris a speck barely visible without the aid of a microscope. 細(xì)胞的大小是以“微米”為長(zhǎng)度單位。微米是一米的一百萬(wàn)分之一，25000微米等于一寸。人體正常細(xì)胞的評(píng)價(jià)圓徑約十微米，肉眼勉強(qiáng)可以看得到，不需要顯微鏡的幫助。 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. 研究關(guān)于“細(xì)胞”是生物學(xué)的分支，成為細(xì)胞生物學(xué)。在最微小水平針對(duì)細(xì)胞的結(jié)構(gòu)及功能的研究成為分子生物學(xué)。 All cells consist of protoplasm, the “l(fā)iving jelly.” The protoplasm of a typical cell forms three vital partsthe 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 11) 所有細(xì)胞都是以“原生質(zhì)”，又稱“生命膠質(zhì)”所形成的。典型細(xì)胞的原生質(zhì)形成了三個(gè)重要部分，細(xì)胞膜、細(xì)胞質(zhì)和細(xì)胞核。細(xì)胞膜圈住了細(xì)胞的其他結(jié)構(gòu)。大部分的化學(xué)反應(yīng)都在細(xì)胞核周?chē)?，?xì)胞質(zhì)完成的。被自己的膜包圍的細(xì)胞核是細(xì)胞的控制中心。the cells Membrane細(xì)胞膜 Cells can survive only in a liquid medium that brings in food and carries away waste. For onecelled organisms this fluid is an external body of waterthe ocean, a lake, or a stream. For manycelled plants and animals, however, the medium is part of the organismin plants, the sap。 in animals, the blood. 細(xì)胞只能存活在能供養(yǎng)分又能排除廢物的液體媒介中。對(duì)單細(xì)胞生物來(lái)說(shuō)，這就是細(xì)胞外的液體，如：大海里、河里或水流中。在對(duì)多細(xì)胞生物而言，這種媒介就是生物體的一部分，植物以汁液的形式，動(dòng)物以血液的形式。 The cell membrane is semipermeable, or differentially permeablesome 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. 細(xì)胞膜是半滲透性或區(qū)別性的滲透膜，即某些物質(zhì)能滲透。這個(gè)特殊性使細(xì)胞對(duì)細(xì)胞周?chē)晃樟诵枰奈镔|(zhì)而排除掉有害的物質(zhì)，包括細(xì)胞內(nèi)的廢物通過(guò)液體化后排出細(xì)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 moleculeandfluidfilled pocket then breads loose from the membrane to bee 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. 細(xì)胞膜是一種非常薄但確以很堅(jiān)固的蛋白磷脂膜形成。磷脂是一種類似于儲(chǔ)存的脂肪的蛋白物質(zhì)。通過(guò)電子顯微鏡，生物學(xué)家相信細(xì)胞膜有孔，使較小的物質(zhì)完全可以通過(guò)。物質(zhì)可通過(guò)多種方式從細(xì)胞膜進(jìn)入。細(xì)胞膜上的結(jié)構(gòu)，稱“小穴”，可接受化學(xué)信號(hào)再傳到細(xì)胞內(nèi)。小穴還可能參于細(xì)胞蛋白的分配。大的分子可通過(guò)“滲濾”進(jìn)入細(xì)胞內(nèi)，或被細(xì)胞膜內(nèi)體分解，使它們更容易的進(jìn)入細(xì)胞內(nèi)。有些細(xì)胞可通過(guò)“胞飲”方式吞飲較大的物質(zhì)。這個(gè)過(guò)程是通過(guò)細(xì)胞膜在大物質(zhì)形成了“帶”把它包圍著，將它以泡狀的“液泡”引入細(xì)胞質(zhì)，最后包圍解散，大物質(zhì)成功的進(jìn)入細(xì)胞內(nèi)。The cytoplasm細(xì)胞質(zhì) 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. 細(xì)胞質(zhì)