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试论述维生素A的生理功能及缺乏和过量症。

答案

参考答案：

A、生理功能：1、维持暗适应能力：促进视觉细胞内感光物质的合成与再生，防治夜盲症。2、维持上皮细胞组织结构的健全：参与糖基转移酶系统的功能，对糖基起转运和活化作用。3、促进生长发育，维持正常免疫功能。4、增强生殖机能：影响生殖系统的上皮组织。若缺乏，影响雄性动物精子的生成，使雌性动物雌激素分泌的周期变化消失， * * 、子宫、输卵管及胎盘上皮角化，不易受孕或流产。5、防癌作用：VA可促进上皮细胞正常的分化，抑制癌变；胡萝卜素捕捉自由基，猝灭单线氧，提高抗氧化能力。6、参与维持正常骨质代谢：若缺乏会使破骨细胞数目减少，成骨细胞功能失调，导致骨膜骨质过度增生、骨腔变小，牙齿的珐琅保护层出现裂纹和凹陷。B、缺乏症：①暗适应能力降低及出现夜盲症。②皮肤干燥症及干眼病。③儿童、老人易引起呼吸道炎症。④血红蛋白合成代谢障碍，免疫功能低下，生长发育迟缓。C、过量：①破骨细胞活性增强，导致骨脱钙，脆性增加，生长受阻，长骨变粗及关节疼痛。②皮肤干燥、发痒、鳞样皮疹，脱发等。③易激动、疲乏、恶心、呕吐、腹泻、肌无力、肝脾肿大、黄疸等。④血液中血红蛋白和钾水平下降，凝血时间延长，易出血。⑤是一种确认的致癌原，孕妇在妊娠早期大量摄入VA娩出畸形儿的相对危险度为25.6。⑥VC可解除VA毒性的影响。

单项选择题

Passage twoEducating girls quite possibly yields a higher rate of return than any other investment available in the developing world .women’s education may be unusual territory for economists ,but enhancing women’s contribution to development is actually as much an economic as a social issue .and economics ,with its emphasis on incentives ,provides guideposts that point to an explanation for why so many girls are deprived of an education Parents in low-income countries fail to invest in their daughters because they do not expert them to make an economic contribution to he family :girls grow up only to marry into somebody else’s family and bear children .Girls are thus seen as less valuable than boys and kept at home to do housework while their brothers are sent to school-the prophecy becomes self-fulfilling ,trapping women in a vicious circle of neglect. An educated mother ,on the other hand ,has greater earning abilities outside the home and faces an entirely different set of choices. She is likely to have fewer but healthier children and can insist on the development of all her children ,ensuring that her daughters are given a fair chance .The education of her daughters then makes it much more likely that the next generation of girls ,as well as of boys ,will be education and healthy . The vicious circle is thus transformed into a virtuous circle. Few will dispute that education women has great social benefits.But it has enormous economic advantages as well .Most obviously ,there is the direct effect of education on the wages of female workers.Wages rise by 10 to 20 percent for each additional year of schooling. Such big returns are impressive by the standard of other available investments ,but they are just the beginning .Education women also has a significant impact on health practices,including family planning.

By saying“…the prophecy becomes self –fulfilling…” （Lines45，para.2）.the author means that ( )

A．girls will turn out to be less valuable than boys

B．girls will be capable of realizing their own dreams

C．girls will eventually find their goals in life beyond reach

D．girls will be increasingly discontented with their life at home
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多项选择题

肾源性水肿常伴有

A．静脉压升高

B．低蛋白血症

C．高血压

D．眼底改变

E．尿液改变
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