Tissue processing

 TISSUE PROCESSING

Fixation:

Purpose: Fixation is the initial step in tissue processing that aims to preserve the structure and integrity of cells and tissues. It prevents degradation, autolysis, and bacterial contamination.

Method: Tissues are immersed in a fixative solution (e.g., formalin) that stabilizes cellular structures by cross-linking proteins, preserving cellular morphology.

Dehydration:

Purpose: Dehydration involves the removal of water from the fixed tissues to prepare them for embedding in a solid medium. This step prevents water-induced artifacts during subsequent processing.

Method: Tissues are gradually dehydrated by passing them through a series of alcohol solutions of increasing concentration.

Clearing:

Purpose: Clearing is the process of replacing the dehydrating agent (alcohol) with a substance that is miscible with the embedding medium. It renders tissues transparent, allowing for better visualization during microscopic examination.

Method: Tissues are immersed in a clearing agent (e.g., xylene) that displaces the alcohol. This step prepares the tissue for embedding.

Embedding:

Purpose: Embedding involves placing dehydrated and cleared tissues into a supporting medium (embedding medium) that solidifies, allowing for the preparation of thin sections for microscopy.

Method: Tissues are embedded in a suitable medium (e.g., paraffin wax for routine histology) and allowed to solidify. This process facilitates the cutting of thin sections for microscopy.

Sectioning:

Purpose: Sectioning involves cutting thin slices (sections) of the embedded tissue for mounting on microscope slides. This step allows for the examination of cellular and tissue structures.

Method: Microtomes or other cutting devices are used to obtain thin and uniform sections from the embedded tissue block. The sections are then mounted onto glass slides.

Staining:

Purpose: Staining enhances the contrast of cellular and tissue structures, making them more visible under the microscope. Different stains highlight specific components, such as nuclei, cytoplasm, or connective tissues.

Method: Sections are treated with various dyes or stains, each targeting specific cellular components. Common stains include hematoxylin and eosin (H&E), which provides a general overview of tissue structures.

Cover Slipping:

Purpose: Cover slipping involves placing a coverslip over the stained tissue section to protect it and provide a clear, flat surface for microscopy.

Method: A thin layer of mounting medium is applied to the stained tissue section, and a coverslip is carefully placed over it. The mounting medium ensures optical clarity and preserves the stained features.

Each stage in tissue processing plays a crucial role in preparing biological specimens for microscopic analysis, contributing to the accurate diagnosis and understanding of diseases.