In the following web pages about histological techniques, we are going to describe the experimental procedures that, starting from living tissues, allow us to get tissue sections stained and ready to be observed with microscopes. There are web pages dealing with getting the samples, fixation, embedding, sectioning, staining, and visualization of tissues. The instruments to manipulate and process the samples are also introduced, highlighting what they are useful for, but not explained in detail how they operate. A section with protocols and recipes of the more common techniques and solutions is also available.
Most histological techniques are designed for processing of animal and plant samples intended to be studied under the microscope, both light and electron microscopes. These techniques are necessary because a) besides a few cases, tissues do not usually show colors or contrasted structures that allow a fine and detailed study, and b) many tissular and cellular features cannot be distinguished by simple eye but with the help of microscopes. Therefore, samples have to be processed to enhance and discern the structures to be studied. In addition, histological techniques prevent the degradation of samples and preserve the tissular features.
There are quick and simple procedures to study living tissues and cells, known as vital techniques. Intravital techniques make possible the observation of tissues and cells in the body, that is, in situ. For example, the study of the blood flow inside the blood vessels. More complex are the supravital techniques, that allow the study of tissues and cells that have been removed from the body, and keep them alive in vitro. For example, cell and tissue cultures..
Postvital histological techniques entail the dead of the cells, but the morphological and molecular features of the tissue are preserved as much as possible, which depends on the type of histological procedure. The following web pages in this section are dealing with postvital techniques, since they are the most common techniques in the histology laboratories.
The goal of every histological technique is to study the general and fine structure of tissular components. These features should be the same features that the tissues had in the living animal. Although the current histological techniques are designed to preserve the tissular features during the technical process, all techniques introduce more or less important modifications of the tissues. These alterations are known as artifacts, and we should keep them in mind when we are studying the processed tissues under the microscope.
A wide variety of histological techniques have been elaborated during the last centuries. Some of them are used for general assessment of tissues and organs, and some allow a really detailed study of the tissular features, or even of a single component of that tissue. The type of technique and its modifications should be chose depending on the tissue we want to study and on what we want to study in it. For example, animal and plant tissues requires different technical approaches, a bone and a brain need also particular steps in the technical process. In the next web pages, the most general histological techniques will be shown.