The Digestive System At the beginning of the twentieth century, it was known tha
ID: 47237 • Letter: T
Question
The Digestive System
At the beginning of the twentieth century, it was known that the pancreas, a small organ near the stomach, secreted digestive juices into the duodenum, which connects the stomach with the small intestine. This happened whenever partially digested food entered the duodenum from the stomach. The question was whether the signal that started the pancreas working was transmitted by the nervous system or by a chemical substance carried by the blood. At the time, there were known examples of both nerve-stimulated organs and chemical-stimulated organs. No other stimulating mechanism was known.
To decide the issue, two physiologists, W. M. Bayliss and E. H. Sterling, cut all the nerves going to and from the duodenum of an experimental animal. All blood vessels to and from the duodenum were left in place. They also inserted tubes to detect the flow of digestive juices from the pancreas to the duodenum.
The result of this experiment was that, when food entered the duodenum of the experimental animal, the pancreas secreted digestive juices.
Which of the following is a hypothesis from this study? Note: More than one of these could be a hypothesis. Be sure to check every statement that is a hypothesis.
1)When the nerves are cut the pancreas still secretes digestive enzymes into the duodenum.
2)The signal from the duodenum to the stomach is transmitted by chemical substances carried in the blood.
3)How does the duodenum signal the pancreas?
4)The signal from the duodenum to the pancreas is transmitted by nerves.
5)The pancreas secretes digestive enzymes whenever partially digested food enters the duodenum from the stomach.
6)If all the nerves to and from the duodenum are cut, the signal will not be transmitted and the pancreas will not secrete enzymes into the duodenum.
7)If all the nerves to and from the duodenum are cut, the signal will be transmitted and the pancreas will secrete enzymes into the duodenum.
Explanation / Answer
2)The signal from the duodenum to the stomach is transmitted by chemical substances carried in the blood.
3)How does the duodenum signal the pancreas?
4)The signal from the duodenum to the pancreas is transmitted by nerves.
5)The pancreas secretes digestive enzymes whenever partially digested food enters the duodenum from the stomach.
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