tailieunhanh - Cracking the Toefl IBT 2009 edition part 48

Part I of this book gives a brief outline on how the test is organized. Part II helps you familiarize yourself with the basic concepts tested on the TOEFL. Parr III presents you with strategies and tips for the questions and tasks on the test. Pare IV provides you with a full-length practice exam with answers and explanations. | TOEFL Reading 28 of 39 __ 00 08 45 28. The word it in the passage refers to A B C D secretin small intestine bloodstream pancreas Hormones in the Body Until the beginning ol 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. essentially on electrical impulses These impulses were thought to be the engine lor thought emotion movement and internal processes such as digestion However experiments by William Bayliss and Ernest Starling on the chemical secrelm. which is produced in the small intestine when food enters the stomach eventually challenged that view From the small intestine secretin travels through the bloodstream to lhe pancreas There it stimulates the release ol digestive chemicals in this fashion the intestinal cells that produce secretin ultimately regulate the production ol different chemicals in a different organ the pancreas Such a coordination ol processes had peen thought to require control by the nervous system Bayliss and Starling showed that it could occur through chemicals alone This discovery spurred Starling to com the term nomone to refer to secretin taking it from lhe Greek word ttwmm. meaning to excite or to set m motion A normone is a chemical produced by one tissue to make things happen elsewhere. 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 secrete hormones tSreclly into the bloodstream. Such glands include the thyroid and lhe pituitary The exocrine system consists ol organs and glands mat produce substances that are used outside lhe bloodstream primarily lor digestion The pancreas is one such organ although it secretes some chemicals into the blood and thus Is also part ol the endocrine system Much has been teamen about hormones since their discovery Some play such key roles in .