问题 单项选择题 B1型题

下列对“视网膜色素变性”描述正确的是()。

A.双颞侧偏盲

B.向心性视野缩小

C.中心暗点

D.生理盲点扩大

E.同侧偏盲

答案

参考答案:B

解析:1.视盘水肿的视野改变为生理性盲点的扩大。2.视交叉病变最典型的视野改变为双颞侧偏盲,因为是交叉处的神经纤维主要来自于双眼鼻侧的视网膜。3.黄斑出血的视野改变为中心暗点。4.视网膜色素变性的视野改变为周边视野向心性缩小。

名词解释
单项选择题

Imagine eating everything delicious you want with none of the fat. That would be great, wouldn’t it

New "fake fat" products appeared on store shelves in the United States recently, but not everyone is happy about it. Makers of the products, which contain a compound called olestra, say food manufacturers can now eliminate fat from certain foods. Critics, however, say the new compound can rob the body of essential vitamins and nutrients and also cause unpleasant side effects in some people. So it’s up to consumers to decide whether the new fat-free products taste good enough to keep eating.

Chemists discovered olestra in the late 1960s, when they were searching for a fat that could be digested by infants more easily. Instead of finding the desired fat, the researchers created a fat that can’t be digested at all.

Normally, special chemicals in the intestines (肠道) "grab" molecules of regular fat and break them down so they can be used by the body. A molecule of regular fat is made up of three molecules of substances called fatty acids.

The fatty acids are absorbed by the intestines and bring with them the essential vitamins A, D, E and K. When fat molecules are present in the intestines with any of those vitamins, the vitamins attach to the molecules and are carried into the bloodstream.

Olestra, which is made from six to eight molecules of fatty acids, is too large for the intestines to absorb. It just slides through the intestines without being broken down. Manufacturers say it’s that ability to slide unchanged through the intestines that makes olestra so valuable as a fit substitute. It provides consumers with the taste of regular fat without any bad effects on the body. But critics say olestra can prevent vitamins A, D, E and K from being absorbed. It can also prevent the absorption of carotenoids (类胡萝卜素), compounds that may reduce the risk of cancer, heart disease, etc.

Manufacturers are adding vitamins A, D, E and K as well as carotenoids to their products now. Even so, some nutritionists are still concerned that people might eat unlimited amounts of food made with the fat substitute without worrying about how many calories they are consuming.

The result of the search for an easily digestible fat turned out to be ()。

A. just as anticipated

B. commercially useless

C. quite unexpected

D. somewhat controversial