1 56 PHYSIOLOGY FOR BEGINNERS, CHAP.. 



situated on the under side of the anterior edge of the 

 liver. 



The Functions of the Liver. The secretion of bile is 

 one of the functions of the liver. It is formed by the hepatic 

 cells. These draw the substances they require from the blood 

 in the capillaries of the lobule, and they themselves make the 

 special bile salts and pigments of the bile. The bile so 

 formed passes from the hepatic cells into the minute passages 

 between the cells, thence to the small bile ducts between the 

 lobules, and so to the main duct. The bile is always being 

 formed, and in this respect its secretion differs from that of the 

 saliva, gastric juice, and pancreatic juice, which .are generally 

 formed only when food has been taken. When digestion is 

 not going on the bile passes into the gall-bladder, and is 

 sent on from the gall-bladder into the duodenum only when it 

 is wanted to act on the chyme. The quantity of bile secreted 

 in twenty-four hours is about two pints. 



Another function of the liver is to store up carbohydrates. 

 The portal vein brings to the liver a large quantity of sugar 

 which has been absorbed in the intestines. The sugar is in 

 solution in the plasma of the blood of the portal vein. Some 

 of this sugar passes out of the capillaries in the liver with the 

 lymph which exudes through the capillary walls, and is taken 

 up by the hepatic cells which then make out of the sugar a 

 starch-like substance called glycogen, storing it up in the 

 substance of the cells in the form of granules or small masses. 

 Glycogen is far less soluble than sugar, and it is stored in the 

 hepatic cells in the solid condition. Much of the carbo- 

 hydrates absorbed from a meal are in this way taken up and 

 stored in the liver are, in fact, intercepted on their way to 

 the general circulation. By this means the blood of the 

 general circulation is prevented from becoming too rich in sugar, 

 as it would otherwise be after a good meal. Sugar is one of 

 the substances which the blood brings to the tissues ; there 

 is always a small quantity of sugar in the blood, and as this is 

 used up some of the glycogen in the liver is turned into sugar, 

 and is discharged from the liver cells into the blood. In this 

 way the sugar in the blood is always kept at the proper amount. 

 The liver lays down most glycogen after a meal containing 

 much carbohydrate food has been taken. But an animal can 



