2 00 Houo a Complex Animal Uses Food unit iv 



the bloodstream from dog to dog. This also be partly responsible for the stimula- 

 experiment and similar ones were re- tion of the intestinal glands. Secretin is 

 peated, always with the same results. For one of many "chemical messengers" in 

 this reason the experimenters concluded the body. Such substances that are ear- 

 that there is a substance carried by the ried in the blood and act as chemical 

 blood which stimulates the pancreas; they messengers are called homiones. There is 

 called it secretin (see-cree'tin). believed to be a different hormone which 

 Secretin gets into the blood from the stimulates the liver and perhaps another 

 mucous membrane of the small intestine, for the gastric glands. 

 When the first food materials from the The action of digestive glands can be 

 stomach arrive in the small intestine, slowed up as well as increased. Dr. Wal- 

 they stimulate some mucous membrane ter B. Cannon of Harvard University has 

 cells to form secretin. The secretin enters demonstrated that anger or other excite- 

 the blood. It circulates with the blood ment interferes seriously with the secre- 

 and promptly reaches the pancreas. tion of gastric juice in a cat. You can 

 When it arrives there it causes that gland read an account of his experiments in his 

 to secrete very actively. Secretin may book, The Wisdoin of the Body. 



Questions 



1. Name in order the parts of the digestive tube or alimentary canal. 

 How long is it? How long does it take food to pass from end to end? 



2. Where in the body is food constantly needed? If it is carried by the 

 blood, explain through what it must pass to get into the blood. 

 Which substances can diffuse through the walls of the digestive tube 

 and blood vessels? Which cannot? 



3. What is meant by digestion? Why is this called a chemical change? 



4. Explain intermediate and end products of digestion. Give examples. 

 How does the number of amino acids compare with the number of 

 different proteins? 



5. What is the result of adding saliva to cooked starch? What kind of 

 substance in saliva changes starch to sugar? What is the name of this 

 substance? 



6. Define catalyst. How do enzymes differ from other catalysts? In 

 which cell activities do enzymes help? 



7. What is the work of a gland? Define the word secrete. Describe a 

 microscopic gland and name two kinds of microscopic glands that 

 help in digestion. 



8. Name tlirce gland organs that lie outside the digestive tube and that 

 help in digestion. How do they differ from gastric glands? How does 

 the gall bladder function? 



9. State four ways in which the tongue functions. Describe the lining 

 of the mouth and the whole digestive tube. Name three substances 

 making up a tooth. What starts the secretion of the salivary glands? 



