[Sidenote: Products formed in the body from digested carbohydrates]
The products produced by the digestion of carbohydrates are absorbed
from the alimentary canal in the form of glucose and smaller quantities
of levulose, and acetic, butyric and lactic acids. This glucose passes
into the blood-vessels of the intestines. These blood-vessels unite to
form the portal vein which supplies blood to the liver.
[Sidenote: Conversion of glucose into glycogen]
[Sidenote: Percentage of glucose in blood]
The chief function of the liver is to regulate the sugar contained in
the blood. The liver converts this glucose into glycogen and also acts
as a reservoir in which carbohydrates are stored in the form of glycogen
until needed by the body. From this glycogen, glucose, or blood-sugar,
is again produced when the consumption from the circulation is greater
than the supply. Moreover, the liver possesses the power to produce
glucose when no carbohydrates are eaten, as glucose can be produced from
proteids. The percentage of glucose in the blood remains, or should
remain about level, averaging .15 of 1 per cent. It may seem odd at
first that the quantity of glucose in the blood remains so nearly level,
when the quantity absorbed from the digestive organs, and that utilized
in work, is so variable. The control of sugar in the blood is of very
great importance in the body-metabolism or life-processes.
[Sidenote: Uses of glucose in the body]
The chief use of glucose, and of other forms of digested carbohydrates
is in the formation of heat and energy. Glucose is oxidized chiefly
in the muscles, producing carbon dioxid, water, and some lactic acid.
Another function of glucose in the blood is to build up or form fat. Fat
is a form of stored food which is not so readily available for use as
are glycogen and glucose.
To use a homely figure of comparison, the energy-producing substances
of the human body--glucose, glycogen, and fat--may be compared to the
movement of merchandise in ordinary commerce. We could say that the
glucose of the blood is as merchandise in the hands of the people,
ready to be consumed. The glycogen of the liver would represent goods
in the hands of the retailer, while the fat which is stored in larger
quantities would be represented by merchandise in warehouses.
[Sidenote: Fat produced from carbohydrates]
Many interesting experiments have been conducted to prove that fat can
be produced from carbohydrates. For instance, during a given period of
time a pig was fed daily upon food containing half a pound of fat, and
gained during the period nine pounds of fat. Such facts prove beyond all
possibility of doubt that carbohydrates are converted into fat in the
animal body.