HT Tissue Processing 1 — Questions and Answers

Question 1: What is the first step in tissue processing?

Embedding
Dehydration
Fixation (Correct answer)
Clearing

Correct answer: Fixation

Fixation is the critical first step in tissue processing, immediately following tissue collection. Its primary purpose is to rapidly preserve the tissue's cellular and molecular components, preventing autolysis (self-digestion) and putrefaction (bacterial decomposition). This step is essential for maintaining the tissue's architecture and integrity, which is crucial for accurate microscopic examination and diagnosis.

Question 2: Why is tissue dehydration important in processing?

It prevents tissue hardening.
It removes lipids.
It allows tissue to be infiltrated with embedding media. (Correct answer)
It facilitates staining.

Correct answer: It allows tissue to be infiltrated with embedding media.

Tissue dehydration is a crucial step where water is progressively removed from the tissue using ascending concentrations of alcohol. This is necessary because most embedding media, such as paraffin wax, are not miscible with water. By removing water, the tissue becomes receptive to subsequent clearing agents and ultimately allows for proper infiltration with the embedding medium, which is vital for sectioning.

Question 3: What is the purpose of clearing in tissue processing?

To remove the fixative.
To prepare tissues for embedding.
To make tissue transparent. (Correct answer)
To harden tissue for sectioning.

Correct answer: To make tissue transparent.

Clearing is the step after dehydration where alcohol is replaced by a clearing agent, such as xylene. The primary purpose of clearing is to make the tissue transparent, which is necessary because the refractive index of the clearing agent is similar to that of the embedding medium. This transparency allows for better visualization during embedding and ensures complete infiltration of the wax into the tissue.

Question 4: Which embedding media is commonly used in tissue processing?

Celloidin
Paraffin wax (Correct answer)
Resin
Glycol

Correct answer: Paraffin wax

Paraffin wax is the most commonly used embedding medium in routine histology due to its excellent sectioning properties and ease of use. It provides firm support to the delicate tissue, allowing for very thin sections to be cut without distortion or damage. While other media exist for specialized purposes, paraffin remains the standard for general diagnostic work.

Question 5: How does tissue fixation help preserve the sample?

By removing water.
By maintaining cellular integrity.
By preventing bacterial growth.
By preventing cellular breakdown. (Correct answer)

Correct answer: By preventing cellular breakdown.

Tissue fixation preserves the sample by rapidly halting all cellular processes, including autolysis (self-digestion by enzymes) and putrefaction (decomposition by bacteria). This prevents the breakdown of cellular components and maintains the tissue's structural integrity and molecular composition. Effective fixation is crucial for accurate microscopic examination and diagnosis, ensuring the tissue remains in a life-like state.

Question 6: What is the role of paraffin wax in tissue embedding?

It prevents the tissue from shrinking.
It makes the tissue more elastic.
It preserves the cellular structure. (Correct answer)
It increases tissue transparency.

Correct answer: It preserves the cellular structure.

Paraffin wax plays a vital role in tissue embedding by providing a rigid matrix that supports the delicate tissue structure. Once the tissue is infiltrated with molten wax and then cooled, the wax solidifies, allowing for extremely thin sections to be cut without distortion or damage. This preservation of cellular structure is essential for accurate microscopic analysis and diagnosis.

Question 7: What does over-dehydration of tissue lead to?

Better tissue clarity.
Improved embedding.
Distortion of tissue structure. (Correct answer)
No effect on tissue quality.

Correct answer: Distortion of tissue structure.

Over-dehydration occurs when tissue is left in dehydrating agents for too long or in excessively strong concentrations. This can lead to excessive shrinkage and hardening of the tissue, making it brittle and difficult to section properly. Ultimately, over-dehydration results in significant distortion of the tissue's cellular and architectural structure, compromising diagnostic quality and interpretation.

Question 8: Which of the following is true regarding tissue sectioning?

Thicker sections provide better clarity.
Sections must be cut very thin for microscopic examination. (Correct answer)
The sectioning process does not affect the tissue's appearance.
Thinner sections can be too fragile to handle.

Correct answer: Sections must be cut very thin for microscopic examination.

For effective microscopic examination, tissue sections must be cut extremely thin, typically between 3-5 micrometers. This allows light to pass through the tissue, enabling clear visualization of individual cells and their internal structures without overlapping or obscuring details. Thicker sections would result in a blurry or opaque image, hindering accurate diagnosis and analysis.

Question 9: What is the common temperature used for paraffin embedding?

60-65°C (Correct answer)
35-40°C
70-75°C
50-55°C

Correct answer: 60-65°C

Paraffin wax embedding is typically performed at a temperature range of 60-65°C. This temperature is crucial because it ensures the paraffin wax is molten enough to fully infiltrate the tissue, yet not so hot as to cause excessive tissue shrinkage or damage. Maintaining this specific temperature allows for optimal embedding and subsequent sectioning without compromising tissue integrity.

HT Tissue Processing 1

What is the first step in tissue processing?