Histology

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Author:
me1issa_june@hotmail.com
ID:
54410
Filename:
Histology
Updated:
2010-12-08 19:01:10
Tags:
histology histotechnology
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Description:
Overall histotechnology review
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  1. Functions of Fixatives
    • 1. Kill the tissue (prevent autolysis)
    • 2. Maintain relationship b/w cells and extracellular substance
    • 3. Increase differences in Refractive Index to increase the contrast b/w different tissue elements
    • 4. Enhance staining (w/ exceptions)
    • 5. Rendering cell constituents insoluble (especially proteins)
    • 6. Make tissue firmer iot make gross dissection easier
  2. Actions of Fixatives
    • 1. Inactivate enzymes
    • 2. Kill bacteria/molds
    • 3. Make tissue more receptive to dyes
    • 4. Modify tissue constituents for the maximum retention of form throughout processing
  3. Effects of overheating tissue
    • 1. Pyknotic, over-stained nuclei
    • 2. Loss of enzyme activity
    • 3. Loss of antigenicity
    • 4. False localization of nucleic acids
    • 5. Lysis of RBCs
  4. Physical methods of fixation
    • 1. Heat
    • 2. Desiccation
  5. When is desiccation used for fixation?
    Air drying of touch preps for Wright staining
  6. Methods of Fixation
    • 1. Physical
    • 2. Chemical
  7. Classification of Chemical Fixatives
    • 1. Additive/Non-additive
    • 2. Coagulant/Non-coagulant
  8. How does an Additive Fixative work?
    They chemically link to - and change - the tissue
  9. Common Additive Fixatives
    • Mercuric chloride
    • Chromium trioxide
    • Picric acid
    • Formaldehyde
    • Glutaraldehyde
    • Osmium tetroxide
    • Zinc sulfate/chloride

    MCPFGOZ
  10. Common Non-additive Fixatives
    • Acetone
    • Alcohols
  11. How do Non-additive Fixatives work?
    They dissociate bound water molecules from tissue protein groups
  12. Which fixatives cause shrinkage and hardening with over-exposure?
    Non-additive Fixatives
  13. How do coagulant fixatives work?
    They establish a network in tissue allowing solutions to readily penetrate the interior of the tissue
  14. How do non-coagulant fixatives work?
    The create a gel, making penetration by solutions difficult
  15. Common Coagulant Fixatives
    • Mercuric chloride
    • Picric Acid
    • Zinc salts
    • Acetone
    • Ethyl alcohol
    • Methyl alcohol
    • Cupric sulfate

    MPZAEMC
  16. Common Non-coagulant Fixatives
    • Formaldehyde
    • Glutaraldehyde
    • Osmium tetroxide
    • Potassium dichromate
    • Glyoxam
  17. Which fixative is sometimes considered a coagulant and sometimes a non-coagulant?
    Acetic Acid

    • nucleic acids - coagulant
    • cytoplasm - non-coagulant
  18. Factors affecting fixation
    Temperature - increase => increased rate of fixation and autolysis

    Size of specimen - larger specimen => longer to penetrate and fix

    Volume Ratio - should be 15 - 20 x more fixative than tissue volume

    Time - depends on tissue size/type and fixative

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