问题 问答题 简答题

简述佝偻病的发病机理。

答案

参考答案:

佝偻病是由于维生素D缺乏或代谢障碍所导致的儿童因骨质钙化不良,造成骨骼形成的障碍性疾病。因维生素D具有促进肠道和肾小管对钙磷的吸收和促进骨细胞的转化,有利于骨盐的沉积和骨骼钙化作用。维生素D生化作用的发挥依赖于肝、肾功能的正常,它首先在肝25-羟化酶催化下生成25-(OH)-D3,经血液运送至肾,在肾1-羟化酶催化下生成1、25-(OH)2-D3是维生素D3的活性形式,才能发挥生理功用。当维生素D缺乏或肝肾功能不健全时,同样会造成钙磷代谢紊乱,骨骼形成障碍,而引起佝偻病。

阅读理解

In the course of working my way through school, I took many jobs I would rather forget. But none of these jobs was as dreadful as my job in an apple plant. The work was hard; the pay was poor; and, most of all, the working conditions were terrible.

First of all, the job made huge demands on my strength. For then hours a night, I took boxes that rolled down a metal track and piled them onto a truck. Each box contained twelve heavy bottles of apple juice. I once figured out that I was lifting an average of twelve tons of apple juice every night.

I would not have minded the difficulty of the work so much if the pay had not been so poor. I was paid the lowest wage of that time—two dollars an hour. Because of the low pay, I felt eager to get as much as possible. I usually worked twelve hours a night but did not take home much more than $ 100 a week.

But even more than the low pay, what made me unhappy was the working conditions. During work I was limited to two ten-minute breaks and an unpaid half hour for lunch. Most of my time was spent outside loading trucks with those heavy boxes in near-zero-degree temperatures. The steel floors of the trucks were like ice, which made my feet feel like stone. And after the production line shut down at night and most people left, I had to spend two hours alone cleaning the floor.

I stayed on the job for five months, all the while hating the difficulty of the work, the poor money, and the conditions under which I worked. By the time I left, I was determined never to go back there again.

49. Why did the writer have to take many jobs at that time?

A. To pay for his schooling.

B. To save for his future.

C. To support his family

D. To gain some experience

50. The following facts describe the terrible working conditions of the plant EXCEPT ______.

A. loading boxes in the freezing cold                     B. having limited time for breaks

C. working and studying at the same time        D. getting no pay for lunch time

51. What is the subject discussed in the text?

A. The writer’s unhappy school life.               B. The writer’s eagerness to earn money.

C. The writer’s experience to earn money.      D. The writer’s hard work in an apple plant.

52. How is the text organized?

A. Topic—Argument—Explanation

B. Opinion—Discussion—Description

C. Main idea—Comparison—Supporting examples

D. Introduction—Supporting examples—Conclusion

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