INTRODUCTION TO HISTOLOGY
Courses in Cell Biology usually precede those in Histology.
In these courses Cell Concept or Cell Theory is studied and
the cell is defined as the smallest basic structure of higher organisms
capable of independent existence. Even today the Protozoa represent single-celled
organisms. However, the higher organisms consist of tissues and organs.
Tissues are groups of cells of similar function and origin that form
functional units (and also intercellular connective tissue in most
cases) . The organs represent an even greater measure of complexity
and are composed of various tissues. At an even higher level of organization
there are the organ systems composed of several organs (such as
the gastrointestinal system, respiratory system, cardiovascular system,
endocrine system). Thus the body can be seen to be formed of different
levels of organization, with increasing levels of complexity and each of
which plays important roles in the physiological homeostasis of the body.
LEVELS OF ORGANIZATION
The name "Histology" is derived from the Greek word for a tissue "Histos", and "-logos" = the study of. Today the concept of Histology as a subject includes far more than just the study of tissues, but includes understanding of the structure and function of cells, tissues, organs and organ systems, which can better be described as "Microscopic Anatomy". It is evident from the title that the study of Histology or Microscopic Anatomy involves the use of microscopes (light and electron) as basic tools. In addition to understanding the histology and ultrastructure of cells, tissues and organs, it is also necessary to complement the morphological observations with an understanding of the biochemistry, physiology and biophysics of these structures.
BASIC TISSUES
The body is composed of four basic tissues :
