DIGESTION, CIRCULATION, AND ABSORPTION 279 



c. Paths of Absorbed Foods 



Observations. 1. The absorbed foods now take two different 

 directions ; all but the fats go at once to the liver, through the 

 portal vein; while the fats are carried by the main lymph duct 

 (thoracic duct) to a vein under the left 

 collar bone as indicated above, therefore 

 the fats do not pass directly through the 

 liver but to the heart first. What are 

 the lacteals ? Note. Study Figure 63 

 carefully, forming your own questions 

 and answers. 



2. Fats are absorbed chiefly as fatty 

 acids and glycerin. The cells of the 

 villi reconstruct the fatty acids and 

 glycerin into the microscopic fat parti- 

 cles which are passed on into the small 

 tubes that finally converge to form, in 

 part, the thoracic duct which conveys 

 this fatty food into the general circula- 

 tion. 



3. The digestive tube is, then, a mus- 

 cular tube of varying diameter, lined by FIG. 63. Diagram show- 

 mucous membrane. The muscular coat ing how the food reaches 



1 , i /> -, i . . , . . , the heart to he sent with 



propels the foods and mixes them with the blood to all parts of 

 the liquids present; some of these the body, 

 liquids merely soak the food, others act 



on it chemically, while mucus serves to lubricate the surface. 

 It seems that the glands lining the inner surface of the digestive 

 canal are not sufficient, so several extra glands are provided, 

 such as the salivary glands, pancreas, and liver. Find these 

 glands on a chart. 



Conclusion. Write a brief summary of the paths absorbed 

 foods take in reaching the heart. Copy Figure 63. 



