3.1 Processing, Embedding and Microtomy

Tissue Processing, Embedding & Microtomy Overview

Learning Objectives

  • Key Steps in Histology Workflow: Identify essential processes involved in tissue examination.

  • Tissue Processing: Describes steps to prepare samples for embedding and sectioning.

  • Importance of Embedding in Paraffin Wax: Understand the role of paraffin in preserving tissue morphology.

  • Microtomy Principles: Explain sectioning relevance and its methodological significance.

  • Common Issues in Processing: Learn to identify and solve typical problems encountered during histological preparations.

Key Steps in Tissue Processing

1. Fixation

  • Purpose: Preserves tissue to prevent autolysis and decomposition before further processing.

  • Common Fixative: Formalin (formaldehyde solution) used to maintain tissue morphology.

2. Dehydration

  • Process: Removal of water content from tissues.

  • Method: A series of alcohol baths starting from 70% to reach 100% alcohol concentration.

3. Clearing

  • Objective: Replace the dehydrating agent (alcohol) with a solvent, such as xylene, that mixes well with paraffin wax.

  • Importance of Transparency: Ensures proper infiltration of the wax, enhancing visibility of tissue under microscopy.

4. Infiltration

  • Process: Tissue is saturated with molten paraffin wax, replacing the clearing agent completely.

  • Importance: Prepares the tissue for proper molding and sectioning by ensuring uniformity and preservation.

5. Embedding

  • Description: Placing tissue in a mold filled with molten paraffin, oriented to allow correct cutting planes.

  • Result: Solidified blocks of paraffin with embedded tissues for sectioning.

Microtomy

Overview

  • Function: Cutting very thin sections of paraffin-embedded tissues, typically 3-5 microns thick.

  • Microtome Device: Tool used to create sections thin enough for light penetration and effective staining.

Importance of Thin Sections

  • Light Passage: Essential to allow light to pass through tissues for clear imaging.

  • Staining Efficiency: Thin sections enable stains to adequately highlight different cellular components by enhancing contrast.

Cryotomy

Definition

  • Cryotomy Purpose: Prepares frozen sections for rapid microscopic examinations, preserving cellular structure.

  • Techniques: Involves rapid freezing of tissues followed by using a cryostat to cut sections.

Benefits of Cryotomy

  • Advantages: Rapid diagnosis and preservation of antigens for immunohistochemical analysis.

Summary of Key Processes in Histology

  • Sample Collection: Selection of specimens.

  • Tissue Processing: Fixation, dehydration, clearing, and infiltration.

  • Embedding: Prioritizing proper orientation in paraffin.

  • Microtomy and Cryotomy: Techniques for sectioning tissues for analysis.