1、Unit2. Cells and AgingAging is a normal process accompanied by a progressive alteration of the bodys homeostatic adaptive responses; the specialized branch of medicine that deals with the medical problems and care of elderly person is called geriatrics.衰老是一種正常的生理過程，伴有機體內環(huán)境穩(wěn)定適應性應答的進行性改變。研究老年人的健康問題和保健

2、的一門特殊醫(yī)學分支被稱作老年病學The obvious characteristics of aging are well known; graying and loss of hair, loss of teeth, wrinkling of skin, decreased muscle mass, and increased fat deposits. The physiological signs of aging are gradual deterioration in function and capacity to maintain a constant internal envi

3、ronment (homeostasis) in response to changes in temperature, diet, and oxygen supply. These sings of aging are related to a net decrease in the number of cells in the body and to the dysfunctioning of the cells that remain.衰老的明顯特征眾所周知：頭發(fā)花白和脫落，牙齒脫落，皮膚起皺，肌肉減少，脂肪積存增加。衰老的生理征兆是機體對環(huán)境刺激反應的功能和能力的逐漸退化如同維持機體內

4、環(huán)境穩(wěn)定來應對溫度，飲食和氧氣供應改變的能力減退一樣，機體新陳代謝也減慢了。衰老的這些跡象與機體中細胞數目的凈減少以及存余細胞的功能紊亂有關。The extracellular components of tissues also change with age. Collagen fibers, responsible for the strength in tendons, increase in number and change in quality with aging. These changes in the collagen of arterial walls are as m

5、uch responsible for their loss of extensibility as are the deposits associated with atherosclerosis, the deposition of fatty materials in the arterial walls. Elastin, another extracellular component, is responsible for the elasticity of blood vessels and skin. It thickens, fragments, and acquires a

6、greater affinity for calcium with age changes that may also be associated with the development of atherosclerosis. 組織的細胞外成分也隨著年齡的變化而變化。負責肌腱力量的膠原纖維的數量增加，而質量卻隨著衰老降低。動脈壁上的膠原質的變化與動脈壁伸展性喪失有關，正如動脈粥樣硬化，即動脈壁脂肪物質堆積造成動脈壁伸展性缺失一樣。彈性蛋白是另一種細胞外成分，與血管和皮膚的彈性有關，隨著年齡的變化，它變粗，易斷裂并且與鈣有很大的親和力，這些變化可能也與動脈粥樣硬化的發(fā)生有關。Glucose,

7、the most abundant sugar in the body, may also play a role in the aging process. According to one hypothesis, glucose is added, haphazardly, to proteins inside and outside cells, forming irreversible cross-links between adjacent protein molecules. As a person ages, more cross-links are formed, and th

8、is probably contributes to the stiffening and loss of elasticity in aging tissues.葡萄糖是機體中含量最多的糖類，它在衰老的過程中可能也起作用。根據一個假說，隨機地在細胞內外蛋白質上添加葡萄糖，結果會在相鄰蛋白質分子之間形成不可逆的交聯。隨著人的衰老，會形成更多的交聯，這很可能就是造成衰老的組織僵硬及彈性喪失的原因。Although many millions of new cells normally are produced each minute, several kinds of cells heart c

9、ells, skeletal muscle fibers, nerve cells - cannot be replaced, Experiments have shown that many other cell types have only a limited capability to divide. Cells grown outside the body divide only a certain number of times and then stop. The number of divisions correlates with the donor/s age and wi

10、th the normal life span of the different species from which the cells are obtained. These observations provides strong evidence for the hypothesis that cessation of mitosis is a normal, genetically programmed event. According to this view, an “aging” gene is part of the genetic blueprint at birth, a

11、nd it turns on at a preprogrammed time, slowing down or halting processes vital to life.雖然正常情況下，每分鐘會有好幾百萬的新細胞產生，但有幾種細胞：心臟細胞，骨骼肌纖維細胞，神經細胞是無法替代的。實驗顯示，許多種類的細胞分裂能力有限。在機體外生長的細胞僅僅分裂幾代就停止了。細胞分裂數與捐獻者的年齡和這些細胞來自的不同物種的正常壽命有關。這些發(fā)現為這種假說提供了有力的證據，即（細胞的）有絲分裂的終止是正常的，是由基因決定的。根據這個觀點，衰老基因是出生時就存在的基因藍圖的一部分，在預定的時間里開啟，減慢或停

12、止對生命至關重要的生理過程。Another theory of aging is the free radical theory. Free radicals are electrically charged molecules that have an unpaired electron. Such molecules are unstable and highly active and can easily damage proteins. Some effects are wrinkled skin, stiff joints, and hardened arteries. Free r

13、adical may also damage DNA. Among the factors that produce free radicals are air pollution, radiation, and certain foods we eat. Other substances in the diet such as vitamin E, vitamin C, beta-carotene, and selenium are antioxidants and inhibit free radical formation. The free radical theory of agin

14、g is bolstered by two recent discoveries. Strains of fruitt flies bred for longevity produce larger-than-normal amouts of an enzyme called superoxide dismutase, which functions to neutralize free radicals. Also, injection of genes that lead to production of superoxide dismutase into fruit fly embryo

15、s prolongs their average lifetime.衰老的另一個理論即自由基理論，自由基是含有未配對電子的帶電荷分子。這種分子性質不穩(wěn)定，具有高反應活性，容易損害蛋白質。自由基的影響有：皮膚起皺，關節(jié)僵直，動脈硬化。自由基也可以損害DNA。產生自由基的因素有：空氣污染，放射線，以及我們吃的某些食物。飲食中的其他物質如維生素E，維生素C，-胡蘿卜素以及硒都是抗氧化劑，可以抑制自由基的形成。最近的兩個研究支持了衰老的自由基理論。孕育長壽的果蠅株從而產生超正常量的酶：過氧化物歧化酶，它可以中和自由基。同樣，把產生過氧化物歧化酶生成的基因注入果蠅胚胎中會延長其平均壽命。Whereas

16、some theories of aging explain the process at the cellular lever, others concentrates on regulatory mechanisms operating within the entire organism. For example, the immune system, which manufactures antibodies against foreign invaders, may start to attack the bodys own cells. This autoimmune response might be caused by changes in the surfaces of cells, causing antibodies to attach and mark the cell for destruction. As