2019 年托福考试阅读理解模拟练习题及答案
Hormones in the Body
Up to the beginning of the twentieth century,the nervous system was thought to control all communication within the body and the resulting integration of behavior.Scientists had determined that nerves ran,esntially,on electrical impuls.The impuls were thought to be the engine for thought,emotion,movement,and internal process such as digestion.However,experiments by William Bayliss and Ernest Starling on the chemical cretin,which is produced in the small intestine when food enters the stomach,eventually challenged that view.From the small intestine,cretin travels through the bloodstream to the pancreas.There,it stimulates the relea of digestive chemicals.In this fashion,the intestinal cells that produce cretin ultimately regulate the production of different chemicals in a different organ,the pancreas.
880什么意思
Such a coordination of process had been thought to require control by the nervous system;Bayliss and Starling showed that it could occur through chemicals alone.This discovhero第一季
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ery spurred Starling to coin the term hormone to refer学校哪里有插花培训
to cretin,taking it from the Greek word hormon,meaning “to excite ”or “中译英翻译公司>建造师考试科目to t in motion. ”A hormone is a chemical
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produced by one tissue to make things happen elwhere.n sheva
As more hormones were discovered,they were categorized,primarily according to the process by which they operated on the body.Some glands(which make up the endocrine system)crete hormones directly into the bloodstream.Such
glands include the thyroid and the pituitary.The exocrine system consists of organs and glands that produce substances that are ud outside the bloodstream,primarily for digestion.The pancreas is one such organ,although it cretes some chemicals into the blood and thus is also part of the endocrine system.
修葺
Much has been learned about hormones since their discovery.Some play such key roles in regulating bodily process or behavior that their abnce would cau immediate death.The most abundant hormones have effects that are less obviously urgent but can be more far-reaching and
difficult to track ：They modify moods and affect human behavior,even some behavior we normally think of as voluntary.Hormonal systems are very intricate.Even minute amounts of the right chemicals can suppress appetite,calm aggression,and change the attitude of a parent toward a child.Certain hormones accelerate the development of the body,regulating growth and form;others may even define an individual ’s personality characteristics.The quantities and proportions of hormones produced change with age,so scientists have given a great deal of study to shifts in the endocrine system over time in the hopes of alleviating ailments associated with aging.
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In fact,some hormone therapies are already very common.A combination of estrogen and progesterone has been prescribed for decades to women who want to reduce mood swin
gs,sudden changes in body temperature,and other discomforts caud by lower natural levels of tho hormones as they enter middle age.Known as hormone replacement therapy(HRT),the treatment was also believed to prevent weakening of the bones.At least
