118 



ADVANCED PHYSIOLOGY 



These substances are also taken into the villi (Fig. 64), but 

 not into the blood vessels; they enter the single tube, the 

 lacteal, in the center of each villus, and during their absorption 



appear to be again united into true 

 fat. Although physiologists do not 

 know just where or how this occurs, 

 the fact that true fat rapidly collects 

 in the lacteals during absorption 

 would seem to indicate that the fat is 

 broken up simply to enable it to be 

 absorbed through the intestinal walls. 



Thoracic 

 Duct 



THE PATH TAKEN BY THE ABSORBED 

 CARBOHYDRATES AND PROTEIDS 



Proteid foods and carbohydrates 

 both pass directly into the blood ves- 

 sels. The veins carrying this blood 

 away from the viscera unite and 

 form one large vessel, called the 

 portal vein; this goes to the liver, 

 where it divides into very minute 

 branches; Fig. 65. After passing 

 through the liver, the blood collects 

 once more and flows to the heart. 

 This portal vein, which with these 

 same relations occurs in all back- 

 boned animals, is the only vein in 

 the body which breaks up into 

 branches in the liver on its way to 

 the heart. All the others run directly 

 to the heart. 



Why should the blood from the 



intestine be thus distributed through the liver? It is evident 

 that soon after each meal the largest amount of food stuff is 

 present in the portal vein. If this should pass immedi- 



FIG. 65. DIAGRAM OF 



THE VENOUS CIRCULA- 

 TION OF THE INTESTINE 

 AND LIVER 



