What is Dehydration in Histology?
In
Histology, dehydration is a crucial step in the preparation of tissue samples for microscopic examination. It involves the gradual removal of water from the tissue, which is essential for subsequent embedding in a medium such as
paraffin wax or resin. This process ensures that the tissue maintains its structure and cellular integrity during sectioning and staining.
Why is Dehydration Necessary?
Dehydration is necessary because water is incompatible with embedding media. If not properly dehydrated, tissues can become distorted or damaged. This step ensures that the tissue is adequately prepared for embedding, which is crucial for producing high-quality
histological sections.
How is Dehydration Performed?
The process typically involves passing the tissue through a series of graded
ethanol solutions, starting from lower concentrations (e.g., 70%) and progressing to absolute ethanol (100%). This gradual increase in ethanol concentration allows for the careful removal of water, minimizing tissue shrinkage and distortion.
After the ethanol steps, tissues are often transferred to a clearing agent like
xylene or toluene, which is miscible with both ethanol and the embedding medium. This step further ensures that the tissue is entirely free of water.
What is Mounting in Histology?
Mounting is the final step in the preparation of histological slides. After sectioning and staining, the thin tissue sections are placed on a glass slide and covered with a
cover slip using a mounting medium. This step is essential for preserving the tissue and providing a clear view under the
microscope.
It protects the tissue section from physical damage and contamination.
It preserves the staining, ensuring that colors do not fade over time.
It provides a refractive index that enhances the visibility of the tissue structures under the microscope.
Canada Balsam: A traditional medium that provides excellent optical properties but takes a long time to dry.
DPX: A synthetic resin that dries quickly and provides good optical clarity.
Aqueous media like
glycerol or
gelatin: Used for mounting water-soluble stains or when the tissue cannot be dehydrated.
How is Mounting Performed?
Mounting involves placing a small drop of mounting medium on the tissue section, followed by carefully placing a cover slip over it. It is essential to avoid air bubbles, as they can obscure the view and interfere with microscopy. The slide is then left to dry, allowing the mounting medium to harden and secure the cover slip in place.
Dehydration: Rapid dehydration can cause tissue shrinkage and distortion. It is crucial to follow a graded ethanol series to minimize these effects.
Mounting: Air bubbles and improper alignment of the cover slip can affect the quality of the slide. Careful technique is essential to avoid these issues.
Conclusion
Dehydration and mounting are critical steps in histological preparation, ensuring that tissue samples are well-preserved and clearly visible under the microscope. Proper techniques and careful handling at each stage are essential for producing high-quality histological slides, facilitating accurate and detailed microscopic analysis.
