g. Mechanical Disturbances. Certain static mechanical abnormalities may
result in disease within the body. For example, volvulus or twisting of the intestine on
itself, torsion of the spermatic cord, strangulation of a hernia, and intussusception, are
all often of a purely mechanical basis.
h. Disorders of Metabolism, Growth, or Nutrition. Metabolism has to do with
the total chemical cycle of converting substances into forms that are usable to the body.
Metabolism occurs in two phases.
(1) Anabolism. In anabolism, foodstuffs are broken down (digested) and
reconverted into compounds that can be utilized as energy, or as building blocks for
new tissue cells and substances. In anabolism, living tissue is manufactured from
nonliving substances. This results in growth or replenishment.
(2) Catabolism. Catabolism is the breaking down of the body's complex
substances by wear, tear, and age into waste products of simpler composition for
elimination. Metabolism and growth then are dependent on the body's receiving enough
of the proper foodstuffs in order to supply its needs, in other words, on proper nutrition.
Metabolism and growth are further regulated by the vitamins and hormones. The
hormones are supplied by the ductless glands of the body (the pituitary, thyroid,
parathyroids, pancreas, adrenals, and gonads), and any disorder of these glands will
profoundly disturb growth and metabolism. The vitamins are supplied by the diet; if the
diet or nutrition is unsatisfactory, disturbances in growth and metabolism can result also.
Therefore, metabolism, growth, and nutrition are closely related to one another.
i. Neoplasms (Tumors). Normally, the body grows by multiplication of its cells.
At first, in the embryo, these cells are all alike or undifferentiated, but as they multiply,
they come under the influence of certain factors and take on different forms and
different functions to make up the different tissues, organs, and systems of the body
(that is, they become differentiated). This growth and differentiation is a slow,
methodical, controlled process. However, some cells may not differentiate entirely, but
for some unknown reasons, retain varying degrees of undifferentiation, break free of
their growth control and form a new growth (neoplasm) or tumor. Tumors cause
disease by interfering with the function of normal cells, tissues, and organs. They may
cause pressure on an organ so that its normal cells are destroyed or its blood supply is
shut off. A tumor may fill the cavity of an organ so that the organ wall cannot contract
properly. The tumor may also use up the nutritive materials taken into the body so that
there is not enough for the normal tissues. Tumors are of two types: benign and
(1) Benign. These are more slowly growing, the cells are more
differentiated, the tumor is well separated from the surrounding tissues by its capsule,
and can usually be completely removed surgically.
(2) Malignant. These are more rapidly growing with very little growth
control, and the cells are more primitive or undifferentiated. The cells of the tumor
infiltrate or grow between the normal tissue cells, and are much more difficult to remove