SECRETIONS 101 



granules and fat droplets and, in well-fed animals, masses 

 of glycogen. In the fasting condition the cells are small, 

 cloudy, and have not well-defined contours ; during digestion 

 they are larger, the centre being clear and the periphery 

 containing large granules. 



When a liver is cut through, the liver lobules (Fig. 6) can be 

 seen. These are composed of cells arranged in rows, radiating 



from a vein (the vena centralis) in the 

 centre of the lobules to the circum- 

 ference. But these rows of cells are 

 not isolated, for each cell is connected 

 with those above and below it. 



Between the cells are found both 

 the small bile ducts (the so-called bile 

 capillaries) and the blood capillaries. 

 The bile capillaries stand in the same 

 relation to the liver cells as the lumen 

 of other cells to the gland-cells. Two 

 FIG. 6. CROSS-SECTION OF A cells form the wall of the bile capil- 

 LIVER LOBULE OF A PIG. lary, the latter being formed by two 

 RADIAL ARRANGEMENT OF groove-like depressions in the surfaces 



of two neighboring cells which are 

 fitted together. Each liver cell comes 



in contact with bile capillaries on more than one side. The bile 

 capillaries empty into the bile ducts coursing between the lobules. 

 The blood capillaries originate from the intralobular branch of 

 the portal vein, they traverse the lobules radially and finally join 

 the central vein of the lobule which connects with the intralobular 

 branch of the hepatic vein. The blood capillaries also run 

 between the liver cells, but in such a manner that the blood and 

 bile capillaries never touch each other but are surrounded on all 

 sides by liver cells. Hence, a liver cell or a part of a liver cell is 

 always placed between a blood and a bile capillary. 



The branches of the hepatic artery run only in the intralobular 

 tissue; their capillaries empty in veins which end in the portal 

 vein. The lymph vessels accompany the portal vein. 



4. The formation of bile. 



The secretion of bile can be investigated by means of the biliary 

 fistula. 



The secretion of bile is continuous, but is increased 3-5 

 hours after the taking of food. This increase of secretion 

 during digestion seems to be brought about by absorbed 

 substances which stimulate the liver directly. As such, the 



