When it comes to preserving biological specimens, fixatives play a crucial role in maintaining their cellular integrity and preventing decay. Fixatives are chemicals that stabilize the cell structure by cross-linking or denaturing proteins and other macromolecules. There are five major groups of fixatives, each with a distinctive mode of action. Aldehydes such as formaldehyde and glutaraldehyde work by forming covalent bonds with proteins and nucleic acids. Mercurials like mercuric chloride react with sulfhydryl groups on amino acids to preserve tissues. Alcohols such as ethanol and methanol dehydrate cells and promote protein precipitation. Oxidizing agents such as potassium permanganate and osmium tetroxide oxidize lipids and proteins, leading to tissue preservation. Lastly, picrates like picric acid and picraldehyde form complexes with fixative-loving proteins, which stabilize the cellular structure. Understanding the differences between these fixatives is crucial for choosing the appropriate one for a given application.
What Are the Classification of Fixatives Based on Mode of Action?
Fixatives are important chemicals that allow researchers to preserve the morphology and composition of biological specimens. Fixation essentially involves arresting all cellular and biochemical activities in a specimen, thereby stopping any further changes or degradation of the sample. This process is critical to ensure accurate analysis and observation of specimens under a microscope. Fixatives are categorized based on their mode of action and five major groups have been identified.
The first group of fixatives is aldehydes. Aldehydes are commonly used fixatives in the laboratory because of their ability to create covalent bonds with proteins and other biomolecules. Formaldehyde is the most common aldehyde fixative utilized in the laboratory for routine histological preparations. Other aldehyde fixatives used include glutaraldehyde and acrolein. Formaldehyde is preferred because it’s less toxic, and it doesn’t alter the color of the tissue.
The second group of fixatives are mercurials. Mercury-based fixatives include Bouins and Zenkers solutions, and they’re primarily used for their ability to improve the antigenicity and staining properties of the specimen. However, the use of these fixatives is limited due to the toxicity and environmental hazards associated with mercury compounds.
The third group of fixatives are alcohols. Alcohols, such as ethanol and methanol, are commonly used as fixatives for small specimens that are intended for immunohistochemistry, including small biopsy samples. Alcohol-based fixatives are easy to prepare, but their ability to preserve cell morphology and cytoplasmic components is limited.
The fourth group of fixatives are oxidizing agents. These fixatives are utilized to modify amino acid residues in proteins, and they’re often used in combination with aldehydes or other fixatives to enhance fixation. Examples of oxidizing agents include OsO4, potassium permanganate, and chromic acid.
The fifth and final group of fixatives are picrates. Picric acid is commonly used to fix specimens that contain erythrocytes because it enhances staining and reduces distortion during processing. However, picrates are highly explosive and require special handling procedures to prevent accidents.
The five major groups of fixatives based on mechanism of action include aldehydes, mercurials, alcohols, oxidizing agents, and picrates. The appropriate choice of a fixative will depend on the nature of the specimen and the desired outcome. Researchers should consider the potential toxic effects of the fixatives and undertake appropriate health and safety precautions when using them.
When it comes to preserving fresh tissue or cell specimens for microscopic examination, fixatives are an essential part of the process. There are several types of fixatives to choose from, ranging from simple chemical compounds to more complex solutions designed for specific purposes. In this article, we’ll explore the world of simple fixatives and their benefits in preserving tissues for examination.
Which of the Following Is a Simple Fixative?
When it comes to preserving or hardening fresh tissue or cell specimens for microscopic examination, fixatives are essential. Fixation is the process of preserving cells, tissues, and organs by preventing decay and degradation caused by physical and chemical changes in the body. In histology, a solution is used to harden the tissues to enable microscopic examination. That solution is known as a “fixative.”
There are many types of fixatives available in the market. Simple fixatives are made up of simple chemical compounds. These fixatives require more time for tissue fixation than complex fixatives. Simple fixatives include formalin, picric acid, mercuric oxide, osmic acid, osmium tetroxide, and more. These fixatives are used in laboratories to help researchers study the internal structure of living organisms, tissues, and cells.
Formalin is one of the most commonly used fixatives in histology. It’s a solution of formaldehyde water and is used to preserve tissues for microscopic examination. Formalin also helps in preventing decay and bacterial growth in the tissues. The formaldehyde in the solution reacts with proteins in the tissue to create a stable, solid structure.
Picric acid is another simple fixative that’s commonly used in histology. It’s known for it’s strong yellow color and is used as a fixative for brain tissue and some other organs. One of the benefits of picric acid is that it kills bacteria and fungi that may be present in the tissue, thus helping to preserve the tissue for longer periods.
Mercuric oxide is a fixative that’s used to harden small insects and other small creatures. It’s a toxic substance and therefore should only be used by professionals who’ve access to the necessary protective equipment. Mercuric oxide is also used as a disinfectant and antiseptic.
Osmic acid is a fixative that’s used for cells that contain lipids, such as nerve and brain tissue. Osmic acid is a corrosive chemical and should be used with caution. It reacts with the lipids in the cell membrane to stabilize and harden the tissue, making it suitable for microscopic analysis.
Fixatives are an important part of histology and other scientific disciplines that deal with the study of tissues and cells. Researchers and scientists must use fixatives with caution and take the necessary precautions while handling fixatives, especially toxic substances like mercuric oxide.
Conclusion
In the field of histology and pathology, the selection of an appropriate fixative is crucial in achieving accurate and reliable results. Among the different types of fixatives, the five major fixatives are aldehydes, mercurials, alcohols, oxidizing agents, and picrates. Each of these fixatives has a unique mechanism of action, making them suitable for different types of samples and applications. Fixation is an essential step in preserving tissues and cells for further microscopic examination and analysis. With the proper use of fixatives, it’s possible to maintain the morphological and biochemical integrity of biological samples, providing valuable insights into cellular and tissue structures. As research and medical fields continue to evolve, the knowledge and understanding of the different types of fixatives will remain a critical aspect in ensuring high-quality results.
