Histology & Its Methods of Study

Introduction
Histology: is the study of the microscopic anatomy of cells and tissues of the body and how these tissues are arranged to constitute organs. Histology involves all aspects of tissue biology, with the focus on how cells structure and arrangement optimize functions specific to each organ.
Tissues are made of two interacting components: cells and extracellular matrix. The extracellular matrix consists of many kinds of molecules, most of which are highly organized and form complex structures, such as collagen fibrils and basement membranes. The main functions are:
1- Provide a mechanical support for the cells,
2- Transport nutrients to the cells,
3- Carry away catabolites and secretory products.
Although the cells produce the extracellular matrix, they are also influenced and sometimes controlled by molecules of the matrix. There is, thus, an intense interaction between cells and matrix, with many components of the matrix recognized by and attaching to receptors present on cell surfaces. Most of these receptors are molecules that cross the cell membranes and connect to structural components of the intracellular cytoplasm. Thus, cells and extracellular matrix form a continuum that functions together and reacts to stimuli and inhibitors together.
Each of the fundamental tissues (except the central nervous system) is formed by several types of cells and typically by specific associations of cells and extracellular matrix.
The small size of cells and matrix components makes histology dependent on the use of microscopes. Advances in chemistry, molecular biology, physiology, immunology, and pathology—and the interactions among these fields—are essential for a better knowledge of tissue biology.

Preparation of Tissues for Study
The first step to study the tissues is the preparation of histological sections or tissue slices that can be studied with the aid of the light microscope. Under the light microscope, tissues are examined via a light beam that is transmitted through the tissue. Because tissues and organs are usually too thick for light to pass through them, they must be sectioned to obtain thin, translucent sections and then attached to glass slides before they can be examined.
The ideal microscope tissue preparation should be preserved so that the tissue on the slide has the same structure and molecular composition as it had in the body. However, as a practical matter this is seldom feasible and artifacts, distortions, and loss of components due to the preparation process are almost always present.
The basic steps used in tissue preparation for histology are shown in Figure 1-1