CHAPTER LI 

 THE METABOLISM OF CARBOHYDRATE 



THE digestive processes reduce the carbohydrates to the mono- 

 saccharides dextrose, levulose, and galactose the chief of which 

 is dextrose, since cane-sugar and lactose normally form but an in- 

 significant part of the diet. Dextrose is absorbed unchanged into 

 the portal blood by the activity of the intestinal cells. The portal 

 blood therefore becomes charged with sugar above the content nor- 

 mally present in blood. The excess of sugar acts as a stimulus to the 

 liver, which abstracts the excess, so that the blood leaves that organ 

 supplied with about 0-01 per cent, of sugar the normal content. 

 The diffusible sugar retained by the liver is elaborated into the 

 non-diffusible colloid glycogen, and stored as such. There has been 

 much controversy as to the ultimate fate of the glycogen. The 

 generally accepted view is that there is a reversible ferment action in 

 the liver. The ferment converts sugar into glycogen when the portal 

 blood comes laden with sugar, and glycogen into sugar when the 

 blood comes to the liver impoverished in sugar. 



(1) Dextrose (2) Dextrose 



I 



Glycogen Glycogen 



Fat Carbohydrate portion 

 of protein 



Another view is that glycogen is never again converted to dextrose 

 in life, but is elaborated into fat, or it may possibly be combined to 

 the proteins as a carbohydrate moiety. The balance of evidence is 

 in favour of the first view. 



The glycogen quickly disappears from the liver after death, and 

 dextrose is formed. It is also probable that this process takes place 

 in life, and not only post-mortem. There seems to be good evidence, 

 too, that when blood, with a low dextrose content, is perfused through 

 the liver, it acquires dextrose. It is true that glycogen may give 

 rise to fat under certain conditions, but the available evidence indicates 

 that such fat, when metabolized within the body, is again broken 

 down to glycogen and dextrose (see p. 440). Leaving the liver, the 

 dextrose passes in the blood to the heart, and thence to the system 

 generally, to be katabolized. 



The Katabolism of Dextrose. Three views are held as to the manner 

 in which dextrose is normally broken down within the body. Accord- 



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