Páginas 961 e 962 deste livro estudado em todas as escolas médicas pelo mundo inteiro.
Insulin Is a Hormone Associated with Energy Abundance
As we discuss insulin in the next few pages, it will become apparent that insulin
secretion is associated with energy abundance. That is, when there is great abundance of energy-giving foods in the diet, especially
excess amounts of carbohydrates, insulin is
secreted in great quantity. In turn, the insulin plays an
important role in storing the excess energy. In the case
of excess carbohydrates, it causes them to be stored as
glycogen mainly in the liver and muscles. Also, all the
excess carbohydrates that cannot be stored as glycogen
are converted under the stimulus of insulin into
fats and stored in the adipose tissue. In the case of proteins,
insulin has a direct effect in promoting amino
acid uptake by cells and conversion of these amino
acids into protein. In addition, it inhibits the breakdown
of the proteins that are already in the cells.
Páginas 964 e 965
Insulin Promotes Conversion of Excess Glucose into Fatty Acids
and Inhibits Gluconeogenesis in the Liver. When the quantity
of glucose entering the liver cells is more than can
be stored as glycogen or can be used for local hepatocyte
metabolism, insulin promotes the conversion
of all this excess glucose into fatty acids. These fatty
acids are subsequently packaged as triglycerides in very-low-density lipoproteins and transported in thisform by way of the blood to the adipose tissue anddeposited as fat.
Insulin also inhibits gluconeogenesis. It does this
mainly by decreasing the quantities and activities of
the liver enzymes required for gluconeogenesis.
However, part of the effect is caused by an action
of insulin that decreases the release of amino acids
from muscle and other extrahepatic tissues and in
turn the availability of these necessary precursors
required for gluconeogenesis. This is discussed
further in relation to the effect of insulin on protein