问题 问答题 简答题

简述发热的表现及特点。

答案

参考答案:

(1)体温上升期:此期常有疲乏无力、肌肉酸痛、皮肤苍白、畏寒或寒战等。机理:皮肤苍白是因体温调节中枢发出的冲动经交感神经而引起皮肤血管收缩、浅层血流减少所致,甚或伴有皮肤温度下降。由于皮肤散热减少刺激皮肤的冷觉感受器并传至中枢引起畏寒。中枢发出的冲动再经运动神经传至运动终板,引起骨骼肌不随意的周期性收缩,发生寒战及竖毛肌收缩,使产热增加,产热大于散热,使体温上升。体温上升有两种方式:①骤升型:体温在几小时内达到39~40℃或以上,常伴寒战。小儿易伴惊厥。见于疟疾、大叶性肺炎、败血症、流行性感冒、急性肾盂肾炎、输液反应或某些药物反应。②缓升型:体温逐渐上升在数日内达高峰,多不伴畏寒。见于伤寒、结核病、布氏杆菌病等。

(2)高热期:体温上升达高峰之后保持一定时间,持续时间的长短可因病因不同而有差异。如疟疾可持续数小时,大叶性肺炎、流行性感冒可持续数天,伤寒则可为数周。此期体温已达到或略高于上移的体温调定点水平,体温调节中枢不再发出寒战冲动,故寒战消失;皮肤血管由收缩转为舒张,使皮肤发红并有灼热感;呼吸加快变深;开始出汗并逐渐增多,使产热与散热过程在较高水平上保持相对平衡。

(3)体温下降期:由于病因的消除,致热原的作用逐渐减弱或消失,体温中枢的体温调定点逐渐降到正常水平,产热相对减少,散热大于产热,使体温降至正常水平。表现为出汗多,皮肤潮湿。体温下降有两种方式:①骤降:体温数小时内迅速下降至正常,有时可略低于正常,伴大汗淋漓。见于疟疾、急性肾盂肾炎、大叶性肺炎及输液反应。②渐降:体温在数天内逐渐降至正常,如伤寒。

单项选择题
阅读理解

Animals can move from place to place, but plants cannot. When an animal is under attack, it can run away or fight back.. Plants certainly cannot run away, and they lack teeth and claws. But plants can defend themselves by using both physical and chemical means.

Some plants have their own ways to keep animals away. For example, the leaves of the holly plant have sharp spines (刺) that discourage grass-eating animals. Holly leaves on lower branches have more spines than leaves on upper branches. This is because the lower leaves are easier for most animals to reach.

Some plants, such as the oak tree, have thick and hard leaves that are difficult for animals to eat. Some grasses may contain a sandy material; eating such grasses wears down the animal's teeth.

Many plants also have chemical defenses. Some plants produce chemicals that taste bitter or cause an unpleasant reaction. Some plants may fight against an attack by increasing the production of these chemicals. When a caterpillar (毛虫) bites a tobacco leaf, the leaf produces a chemical messenger. This messenger sends to the roots the information to produce more nicotine. The higher levels of nicotine discourage the caterpillar.

Many plants depend on both physical and chemical defenses. A certain plant in China, for

instance, has prickly (多刺的) leaves, and each prickle contains poisonous venom (毒液) A single experience with this kind of plant will teach an animal to stay away from it in the future.

小题1:The holly plant has more spines on the lower leaves because most animals________.

A.are not tall enough

B.like the lower leaves only

C.are not clever enough

D.can get the lower leaves easily小题2:To defend themselves, oak trees use________.

A.chemical means

B.physical means

C.bitter chemicals

D.sandy materials小题3:How does tobacco protect itself against an attack from a caterpillar?

A.Its leaves fight against the attack by physical means.

B.Its roots send a messenger to discourage the caterpillar.

C.Its roots increase the production of nicotine when it is attacked.

D.Its leaves produce poisonous sand to drive the caterpillar away.小题4:What would be the best title for this passage?

A.Plants and Animals

B.How Plants Defend Themselves

C.Attacks and Defenses

D.How Animals Eat Plant Leaves