【正文】 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。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)整體來發(fā)揮作用的，沒有哪個(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。（約37攝氏度）。s temperature close to 37 176。 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. 女性生殖系統(tǒng)產(chǎn)生、輸送卵子（女性性細(xì)胞），將未受精的卵子排出體外，而當(dāng)精、卵結(jié)合時(shí)，女性生殖系統(tǒng)培養(yǎng)、提供胚胎生長(zhǎng)場(chǎng)所，并孕育新生兒。這些神經(jīng)輸送來自各種感覺器官的信息。神經(jīng)系統(tǒng)更高級(jí)的功能是整合、處理信息。胰腺不僅分泌消化酶，而且分泌胰島素和高血糖素，這兩種激素控制機(jī)體的糖分及淀粉的消耗。s use of sugar and starches. 另一個(gè)腺體，甲狀腺，位于鎖骨之間。它至少分泌八種激素，這些激素對(duì)人體生長(zhǎng)、肝功能及性器官發(fā)育有影響。 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. 內(nèi)分泌系統(tǒng)。身體是通過讓’腎過濾血液來做到這一點(diǎn)的。 The liquid remainder of the food enters the large intestine, or colon, which is about 12 feet ( 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. 液狀的剩余食物進(jìn)入大腸，或結(jié)腸，它大約有12英尺（）長(zhǎng)。這些酶完成食物的化學(xué)分解。接著，食物經(jīng)食管人胃。食物和液體在消化道里被吸收，在腸道里移動(dòng)時(shí)，被分解成小分子物質(zhì)后再進(jìn)入循環(huán)系統(tǒng)。空氣經(jīng)鼻腔、口腔人喉管、氣管。一些細(xì)胞周圍的體液不是直接回流入血管通道，這種體液叫淋巴液，它是流經(jīng)另一個(gè)管道系統(tǒng)——淋巴管而回流人心臟。一半吸收來自肺部的血液，并將血液運(yùn)送到機(jī)體的其余部位，另一半使流經(jīng)全身的血液回流人肺。循環(huán)系統(tǒng)運(yùn)送有用物質(zhì)，排泄廢物。心臟收縮和平滑肌收縮就不是被意識(shí)所控制的。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 ，肌肉收縮產(chǎn)生的熱有助于維持一個(gè)恒定的體溫。s skeleton is made of cartilage that is gradually replaced by bone as the infant grows into an adult.軟骨是一種比一般骨更具韌性的物質(zhì)。顱骨不能運(yùn)動(dòng)，是由于骨與骨之間的連接太緊密。人體有206根骨頭。 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.解剖學(xué)家發(fā)現(xiàn)把整個(gè)人體分成骨骼、肌肉、循環(huán)、呼吸、消化、泌尿、內(nèi)分泌、神經(jīng)、生殖系統(tǒng)以及感覺器官的做法是很有幫助的。 the study of the body39。s structure is called anatomy。其他研究人體的科學(xué)包括生物學(xué)、細(xì)胞學(xué)、胚胎學(xué)、組織學(xué)、內(nèi)分泌學(xué)、血液學(xué)、遺傳學(xué)、免疫學(xué)、心理學(xué)等等。它對(duì)軟組織及人體器官起到支持和保護(hù)作用，并牽動(dòng)骨胳肌，引起各種運(yùn)動(dòng)。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. 關(guān)節(jié)把骨與骨連接起來。Cartilage is a more flexible material than bone. It serves as a protective, cushioning layer where bones e together. It also connects the ribs to the breastbone and provides a structural base for the nose and the external ear. An infant39。一個(gè)嬰兒的骨骼就是由軟骨組成，然后不斷生長(zhǎng)、骨化，使嬰兒長(zhǎng)大成人。這也就使整個(gè)人體可以運(yùn)動(dòng)起來，如走路，運(yùn)動(dòng)軀體某個(gè)部位，如彎曲手指。s defense system. It has antibodies and white blood cells that protect the body against foreign invaders. 循環(huán)系統(tǒng)：機(jī)體的所有部分需要營(yíng)養(yǎng)物質(zhì)和氧氣來使之發(fā)揮功能和生長(zhǎng)，也需要在這些器官所產(chǎn)生的廢物積聚而危害生命之前將其排除。 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. 心臟是一塊被分為幾乎對(duì)等兩半的肌肉。 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. 淋巴系統(tǒng)也是循環(huán)系統(tǒng)的一個(gè)組成部分。 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. 呼吸系統(tǒng)從空氣中攝取氧氣，并將二氧化碳、水蒸氣排出體外。 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.