316 - Multicellular Animals, Especially Man 



the rectum normally generates the "desire to 

 defecate," which tends to follow certain 

 meals, according to the habits of the indi- 

 vidual. The headache and other discomfitures 

 of "constipation" appear to be associated 

 with a prolonged and unnatural distention 

 of the rectum by packed feces, when defeca- 

 tion fails to occur at proper intervals. All the 

 symptoms of the condition can be duplicated 

 in man by merely packing the rectum with an 

 inert mass, such as sterile cotton. This indi- 

 cates that the discomfiture arises not from 

 toxins absorbed from the gut, but from a 

 reflex irritation of the nervous system. 



Different cathartics initiate mass move- 

 ments — (hat is, vigorous and enduring peri- 

 staltic rushes in the small and large intestines 

 — in various ways. Certain drugs (for exam- 

 ple, castor oil) strongly irritate the nerve 

 endings in the mucosa of the tract, and these 

 nerve endings are the receptors of the power- 

 fid reflex movements that follow. Salts (tor 

 example, magnesium sulfate) have a double 



action. In the high concentrations used, they 

 irritate the gastrointestinal receptors; but 

 more important still, a hypertonic solution of 

 such a relatively nonabsorbable salt tends to 

 hold water in the digestive tract, keeping the 

 food mass abnormally fluid even after it 

 passes through the colon. The third type of 

 cathartic (for example, drugs such as cas- 

 cara) acts upon the reflex centers in the cen- 

 tral nervous system (medulla), sensitizing 

 these centers to discharge motor impulses to 

 the musculature of the intestinal tract. 



Regular use of any type of cathartic is to 

 be avoided, because all types are to some ex- 

 tent habit forming and at least slightly dele- 

 terious to the normal digestive and absorp- 

 tive functions. In almost all cases constipation 

 can be avoided by regularizing the defeca- 

 tion habit, bringing it into synchrony with 

 the normal autonomic reflexes of the gastro- 

 intestinal tract; and in rare cases when this 

 procedure is ineffective, a qualified physician 

 should be consulted. 



TEST QUESTIONS 



1. Gastric vacuoles, which are characteristic of 

 unicellular animals generally, have persisted 

 among primitive multicellular animals. Ex- 

 plain, citing at least two specific examples. 



2. Describe the processes of ingestion and di- 

 gestion as they occur in Hydra. 



3. Tubular digestive tracts tend to display more 

 differentiation than saccular tracts. Explain 

 this statement, basing the discussion on the 

 digestive tracts of Hydra and the earthworm. 



4. Explain the importance of the coelomic cav- 

 ity in relation to the "digestive movements" 

 of an animal. 



5. Diagram the digestive tract of man, showing 

 the connections of the various digestive 

 glands. 



6. Describe the general similarity of histological 

 structure that is found in different parts of 

 man's digestive tract. 



7. Identify and locate: (a) the hard palate; (b) 

 the uvula; (c) goblet cells; (d) the gastric 

 glands; (e) the intestinal glands; (I) placoid 

 scales; and (g) the parotid glands. 



8. Brielly discuss man's dentition in relation to 



the teeth of other mammals, especially the 

 rodents, herbivores, and carnivores. 

 9. Briefly explain the [unctions of each juice 

 in terms of its composition: (a) the saliva; 

 (b) the gastric juice: (c) the pancreatic juice; 

 (d) the bile; (e) the intestinal juice. 



10. Assume that a man has eaten a bowl of rice, 

 served with sugar and milk. Make a table to 

 show the complete digestion ol the carbo- 

 hydrate components of this meal. Be sure to 

 specify: 



a. all the different carbohydrates present 

 in the meal 



b. the enzyme or enzymes involved in the 

 digestion of each compound 



c. the glandular source of each enzyme 



d. the end products produced by diges- 

 tion 



e. the part ot the digestive tract in which 

 the digestion occurs 



11. Make similar tallies assuming that the man 

 has eaten: 



a. some olive oil. 



b. some boiled egg albumen (protein) 



