(3) Resistance to infection. The presence of intercellular substance creates
a buffer zone to help prevent the spread of infection from cell to cell. However, some
bacteria produce an enzyme (hyaluronidase) that is capable of breaking down one of
the chief constituents of intercellular substance (a mucopolysaccharide called
hyaluronic acid), thus reducing the viscosity of the intercellular substance and enabling
an infection to spread.
c. Fibrous Intercellular Substance. There are three kinds of formed
intercellular substances that are fibers: collagenic, reticular, and elastic. Chemically,
these fibers are a great deal alike since they are all albuminous proteins. This group of
proteins is characterized by their insolubility in neutral solvents.
d. Amorphous Intercellular Substance. The ground substance of connective
tissue is a nonfibrillar amorphous substance that varies from a fluidlike, to a gellike, to
a firm intercellular cement. When in a liquid state, the ground substance should not be
confused with interstitial fluid, which originates from blood plasma. The amorphous
material is chiefly composed of mucopolysaccharides. Cartilage is composed
predominantly of mucopolysaccharides. As calcium salts deposit in
mucopolysaccharides, bone is formed.
Section III. INTRODUCTION TO PATHOLOGY
116. DEFINITION OF PATHOLOGY
Pathology is the study of disease. Disease can be defined as a derangement of
the normal functioning of one or more of the body processes. This interference with the
normal body functions either prevents them from taking place, or causes them to act in
an abnormal manner. For example, a tumor may obstruct the flow of intestinal contents,
or bacteria may cause irritation or inflammation. In the following text, consideration will
be given to those factors that are responsible for interference with the normal body
functions, in other words, the etiology (causes) of disease.
117. CAUSES OF DISEASE
There are nine major causes of disease (a through i below). Frequently, a
disease may be produced by a combination of these causes, or the same disease may
be caused by different factors in different patients, or the cause may be unknown (j
a. Prenatal Influences. By this is meant those factors that may operate before
birth to produce disease in the offspring; factors may be manifested at birth (congenital
disease) or may not become obvious until later in life.
(1) Heredity. Among prenatal factors, one influence is heredity.
A disease may be genetically transmitted from a parent to offspring. The parents who
transmit the disease to their offspring may or may not have the disease themselves.
Examples of some common hereditary diseases are hemophilia and congenital
dislocation of the hip.