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Tissue Fixation-Lecture 12 10.30.55 AM

Tissue Fixation-Lecture 12 10.30.55 AM - HISTOLOGY LECTURE...

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HISTOLOGY LECTURE # 12 INTRODUCTION TO TISSUE FIXATION Rationale : Fixation is the most essential part in histology. Here is where everything starts. A well fixed tissue is the key for a good slide and therefore a good interpretation for diagnosis. Here we will learn the several types of fixation available their advantages and disadvantages. Objective: Once completed this lecture, the student should be able to: a) Describe the various fixatives and their uses. b) Learn the difference between autolysis and putrefaction c) Differentiate the fixatives that could impact the final results. d) Learn the chemicals and reagents used in each fixative. TISSUE FIXATIVE Introduction Fixation - is the most important step through the process of histology. The purpose of the fixative is to stabilize the protein in the tissue. Once the tissue is removed from the body it will go through a process of self-destruction. This process is known as Autolysis – which starts soon after the cell death creating an enzyme attack, which in place causes the breakdown of protein and eventual liquefaction of the cell. Autolysis is more severe in tissues which are rich in enzymes, such as the liver, brain and kidney, and is less rapid in tissues such as elastic fibers and collagen. By light microscopy, autolyzed tissue presents a `washed-out' appearance with swelling of cytoplasm, eventually converting to a granular, homogeneous mass which fails to take up stains. If tissue is left without any preservation, then a bacterial attack will occur, this process is known as Putrefaction . 1
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2 The objective of fixation is to preserve cells and tissue constituents in as close a life-like state as possible and to allow them to undergo further preparative procedures without change. Fixation arrests autolysis and bacterial decomposition and stabilizes the cellular and tissue constituents so that they withstand the subsequent stages of tissue processing. Fixation should also provide for the preservation of tissue substances and proteins, therefore, it is the first step and the foundation in a sequence of events that culminates in the final examination of a tissue section. FUNCTION OF FIXATIVES A. Help Maintain a proper relationship between cells and extracellular substances: Connective Tissue Fibers: Collagen, Reticulin, Elastin Amorphous ground substances B. Brings out differences in refractive indexes and increases the visibility or contrast between different tissue elements. R.I. = Velocity of light in Air/Velocity of light in a liquid or solid medium C. Render cell constituent’s insoluble, with tissue proteins serving as the primary target for stabilization. ACTION OF FIXATIVES A. Methods of Stabilizing Proteins 1. Heat (Physical method) – this method is becoming more used in the histology laboratories with the introduction of microwave fixation.
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Tissue Fixation-Lecture 12 10.30.55 AM - HISTOLOGY LECTURE...

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