LECTURE XL 

 PHYSIOLOGY OF DIGESTION. 



Definition. —Digestion is a chemical process by which food 

 matters are made soluble and capable of absorption. 



The digestive fluids are saliva, gastric juice, pancreatic juice, 

 bile, and intestinal juice. These are the active agents which bring 

 about the chemical changes necessary to make food matters so- 

 luble. 



Food groups are of two general classes : organic, and inor- 

 ganic. 



The organic group is divided into three sub-groups : car- 

 bohydrates (sugars and starches) ; proteids (egg albumen, casein, 

 gluten, etc.) ; and hydrocarbons (fats and oils). 



The inorganic group includes water, lime, sulphur, phos- 

 phorus, etc. 



COURSE AND HISTORY OF FOOD GROUPS. 



Carbohydrates. — Starch cells are broken up by the teeth 

 and the starch is changed by the saliva, and pancreatic juice, 

 into soluble sugars. Physiologists differ somewhat as to details, 

 but during the process of digestion at least two sugars — dex- 

 trose (grage sugar), maltose, and dextrine, an intermediate body 

 between sugar and starch, are formed. After these chemical 

 changes comes absorption, then distribution. A large part of the 

 starch products are taken into the portal circulation and carried to 

 the liver. The remainder enters the general circulation. The por- 

 tion carried to the liver is there changed back to a form of starch, 

 called glycogen. As the blood loses its sugar, it is resupplied 

 from the liver. Thus the liver becomes a store house for sur- 

 plus sugar and at the same time acts as a balance wheel, in main- 

 taining a uniform percentage of this material in the blood. The 

 sugar is ultimately oxidized, liberating heat, CO2, and water. 

 These are excreted by the skin, lungs and kidneys. 



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