Classification and Composition of Fixatives
About this topic
This comprehensive tertiary topic provides a systematic overview of fixative classification, composition, and specific applications, essential knowledge for students in Zambian university and college programs in cellular pathology and histotechnology. Fixatives are classified by mechanism (aldehydes, oxidizing agents, alcohols, mercurials, picrates) and by use (microanatomical, histochemical, cytological). Students will learn the chemical composition of common fixatives such as 10% Neutral Buffered Formalin, Zenker's, Bouin's, Carnoy's, and B-5, including their active ingredients and target tissues. The module details the advantages and disadvantages of key fixatives like formaldehyde (good penetration, irritant) and glutaraldehyde (excellent for EM, poor penetration). For Zambian diploma and degree students, this knowledge is critical for selecting the appropriate fixative based on diagnostic needs, subsequent staining techniques (e.g., H&E, IHC), and tissue type. Mastery supports exam success and enables effective participation in laboratory protocol development and quality control in Zambian histopathology departments, ensuring optimal tissue preservation for accurate diagnosis.
What you'll practise (50 questions)
- What is the most common fixative used in histopathology laboratories?
- Bouin's fluid is an excellent fixative for testicular biopsies because it preserves nuclear detail well.
- Formalin pigment is an artifact that can form if formaldehyde becomes acidic.
- Mercuric chloride-based fixatives like Zenker's fluid can leave a crystalline deposit in tissue that must be removed with iodine before staining.
- Glutaraldehyde is a better fixative than formaldehyde for preserving tissue antigens for immunohistochemistry.
- Osmium tetroxide is a fixative commonly used for light microscopy of routine biopsies.
- Carnoy's fixative, which contains alcohol and acetic acid, is good for preserving glycogen and RNA.
- What is the term for the artefact pigment that can form in tissues fixed in acidic formalin?
- Mercuric chloride is a component of some fixatives and acts as a mordant to improve tissue staining.
- Bouin's fixative contains picric acid, which stains tissues yellow, requiring a washing step in alcohol before processing.
- Which component of Zenker's fixative is responsible for the formation of mercury pigment artifacts?
- Bouin's fixative is particularly good for fixing hematopoietic (blood-forming) tissues like bone marrow.
- Zenker's fluid is an example of a microanatomical fixative that preserves overall tissue structure.
- Picric acid is both a fixative component and can be used as a yellow acidic dye.
- Which of these fixatives is most appropriate for a lymph node biopsy where immunohistochemistry might be needed later?
- Carnoy's fixative is a good choice when you need to preserve glycogen in a liver biopsy.
- What is the term for the unwanted black/brown crystalline deposits that can form in tissues fixed with mercuric chloride?
- B-5 fixative is specifically recommended for fixing lymph nodes and other hematopoietic tissues.
- Picric acid-based fixatives like Bouin's are ideal for preserving glycogen and carbohydrates.
- Osmium tetroxide is an excellent fixative for preserving lipid membranes and myelin sheaths.
- Which of these fixatives is most likely to be used for a bone marrow trephine biopsy?
- Mercuric chloride-containing fixatives provide excellent nuclear detail but are toxic and require special disposal.
- Alcohol-based fixatives like Carnoy's are good for cytology smears because they act quickly and preserve nuclear detail.
- 'Formalin pigment' can be differentiated from true hemosiderin pigment because it is birefringent under polarized light.
- B-5 fixative must be prepared fresh before use because it is unstable.
- 'Neutral Buffered Formalin' is buffered to prevent the formation of formic acid and formalin pigment.
- Glutaraldehyde provides better ultrastructural preservation than formaldehyde for electron microscopy.
- What is the function of 'acetic acid' in compound fixatives like Carnoy's or Bouin's?
- Bouin's fixative is excellent for preserving glycogen.
- Mercury-based fixatives require a special treatment step to remove crystalline deposits before staining.
- Which of the following fixatives is most appropriate for preserving enzymes for histochemical studies?
- Osmium tetroxide is commonly used as a primary fixative for routine light microscopy.
- B-5 fixative is ideal for tissues that will undergo immunohistochemistry for lymphocyte markers.
- Glutaraldehyde fixation is reversible.
- Which of the following is a characteristic of a 'precipitating fixative' like ethanol?
- Zenker's fluid is an excellent fixative for preserving cytoplasmic detail.
- Carnoy's fixative contains chloroform, which helps to dissolve lipids during fixation.
- Which of the following is an advantage of using 'neutral buffered formalin' over plain formalin?
- Bouin's fixative contains formaldehyde, which acts as the primary cross-linking agent.
- Mercuric chloride improves nuclear staining by acting as a mordant.
- Which of the following fixatives is best suited for preserving phospholipids in tissues?
- Formalin pigment artifact appears as brown-black crystalline deposits within blood vessels and tissues.
- What is the primary role of 'acetic acid' in Carnoy's fixative?
- Bouin's fixative is recommended for fixing tissues that will be used for electron microscopy.
- For which type of tissue is 'B-5 fixative' particularly recommended?
- Carnoy's fixative is good for fixing bloody specimens because it lyses red blood cells.
- What is the main function of 'acetic acid' in Bouin's fixative?
- Glutaraldehyde provides better antigen preservation than formaldehyde for immunohistochemistry.
- Which of these is a 'cross-linking' fixative?
- What is the term for the artifact where formalin-fixed tissue develops dark brown, crystalline deposits?
Answer each question above to see the correct answer and a full explanation.