Question

Briefly explain the purpose of each of the following histological procedures.  

a.   Immersion of fresh tissue in 10% buffered formalin

At the end it will turn in water base.

b.   Embedding tissue samples in paraffin wax

c.   Immersion of paraffin-embedded tissue sections in hydrocarbon solvent before staining

Answer 1

A). To date, formaldehyde as a 10% neutral buffered formalin is the most widely used universal fixative because it preserves a wide range of tissues and tissue components.

Fixation in 10% buffered formalin plays many roles in histochemistry:

• It preserves and stabilizes cell morphology and tissue architecture
• It inactivates proteolytic enzymes that could otherwise degrade the sample.
• It strengthens samples so that they can withstand further processing and staining.
• It protects samples against microbial contamination and possible decomposition (as it is toxic to most common microorganisms like bacteria).

At the end it will turn in water base -

To prevent exposure to formalin gas and formalin pollution of the ethanol dehydration series. This does not have any serious detrimental effects on the quality and characteristics of sections stained as per histological procedures.

B). Embedding tissue samples in paraffin wax -

Embedding is actually a process in which the tissues or the specimens are enclosed in a mass of the embedding medium using a mould. Since the tissue blocks are very thin, they need a supporting medium in which the tissue blocks are embedded.

In histopathology, paraffin wax is used for embedding specimens. Once solidified, the block of paraffin with the embedded specimen is transferred to a microtome (an instrument with a very sharp knife, which cuts 3-4 micron sections of tissue for examination under microscope).

C). Paraffin-embedded tissue sections are immersed in hydrocarbon solvent -

This makes tissues transparent so that paraffin can fully envelop the tissue. And when preparing slides for microscopy, it can remove any remaining wax from slides.

Explanation -

In histology, xylene is used to process and stain tissues. Then these tissues can be used in microscopy. As we already discussed, in tissue processing, tissue has to be embedded in a paraffin medium to support it and allow it to be cut without damaging the tissue. Fixed tissue is then dehydrated to remove water from the tissue. This alcohol is not miscible with paraffin. But Xylene is highly miscible with paraffin. So it is used to process tissues after paraffin embedding.

Thank you.