FUNCTIONS OF THE LIVER 161 



stomach, small intestine, spleen, and pancreas receive blood from 

 the capillaries in those organs and send it to a large vein called the 



fish- 



Among the vertebrates, animals are found with different numbers of chambers in the heart. The 

 heart of mammals is really two separate hearts, each composed of an auricle and a ventricle. 



portal win. This vein breaks up into capillaries in the liver. By 

 means of osmosis the liver cells either take out excess nutrients or 

 give needed sugar to the blood. Another vein, the hepatic vein, 

 then carries the blood with its normal content of nutrients to 

 the inferior vena cava. It takes, approximately, thirty seconds 

 for the blood to make a complete circulation. 



Functions of the liver. The liver, like all other organs, con- 

 sists of cells. These cells use oxygen and food and give up carbon 

 dioxide, water, and urea. The partially disintegrated red cor- 

 puscles are completely destroyed in the liver. The liver uses some 

 of these corpuscles and other substances as a basis for the manufac- 

 ture of bile. The function of bile was discussed in a former chapter 

 (page 132). Excess glucose is stored in the liver in the form 

 of glycogen or animal starch. When the cells of the body need 

 sugar, this glycogen is converted back into glucose and absorbed 

 again by the blood. Protein is not stored in animal cells ; there- 

 fore, excess proteins must be destroyed. This destruction is ac- 

 complished mainly by the liver. The carbon, hydrogen, and oxygen 

 are taken from the protein or ammo-acid and stored as glycogen. 

 Through an oxidation process, urea is formed in the cells from the 

 nitrogen, sulphates from sulphur, and phosphates from phosphorus. 

 These are given into the blood and are extracted by the kidneys. 



