PHYSIOLOGY 173 



Functions of the Liver 



The secretion of the liver is bile and is discharged into the duo- 

 denum of the small intestine by way of the common hile duct. This 

 is an alkaline solution which serves to help neutralize the acidity of 

 the chyme as it comes from the stomach. This with the pancreatic 

 juice brings about the emulsification of fats mentioned above. Cho- 

 lesterin and two pigment materials are excreted in the bile. Bile is 

 secreted continuously, but between meals it is stored in the gall hlad- 

 de7' and supplied in quantity at meal time. 



Besides these digestive and excretory functions the liver serves 

 in another capacity. It is a storehouse for carbohydrates which it 

 converts to glycogen (animal starch) by enzyme action. This sub- 

 stance is also stored in the voluntary muscles. It is easily recon- 

 verted to dextrose for ready oxidation. Most of the protein by- 

 product wea (and uric acid in some forms) is formed in the liver 

 and carried by the blood to the kidneys for excretion. The removal of 

 toxic protein substances and toxic heavy metals is another function 

 of the liver. 



Absorption and Utilization of Food Materials 



The soluble products of digestion are absorbed through the semi- 

 permeable epithelial lining of the intestine into the blood of the 

 adjacent capillaries, or in the case of fats into the lacteal lymphatics 

 and from here into the subclavian vein through the thoracic lymph 

 duct. The blood supplying the intestine is collected by the hepatic 

 portal vein and delivered to the liver. 



The two functions of proteins in the body are: to rebuild debili- 

 tated protoplasm; and help supply heat and energy to the body by 

 oxidation. Carbohydrates and then fats are more economical and 

 efficient as sources of fuel for production of heat and energy. Oxi- 

 dation of protein requires the disposal of much more waste products. 

 The comparative heat production values of the three are as follows: 



One gram of protein z= 4100 small calories* 



One gram of carbohydrate = 4100 small calories 

 One gram of fat = 9305 small calories 



Some portion of the dextrose is distributed and oxidized directly 

 for immediate energy, but much of it is transformed into glycogen 

 by the enzyme glycogenase in the liver. This may be stored here or 



*A small calorie equals the amount of heat necessary to raise one gram of water 

 one degree centigrade under standard conditions, while a large calorie equals the 

 amount of heat necessary to raise one liter of water one degree centigrade under 

 standard conditions. 



