Fixation of special substances

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Fixation of special substances

  1. 1. • In fields of , and fixation is a chemical process by which biological tissues are preserved from decay,thereby preventing from • Fixation terminates ongoing biochemical reactions • It also increase the mechanical strenght or stability of treated tissues.
  2. 2. • • • • • • • Which are to be fixed are following Proteins Lipids Carbohydrates Biogenic amines Nucleic acids Water and lipid soluble substances
  3. 3. • Crosslinking fixatives act by creating covalent chemical bonds between proteins in tissue. • Most commonly used fixative in histology is the crosslinking fixative formaldehyde (also named formalin). • Formaldehyde is the most commonly used fixative for amino acid histochemistry. • Another popular aldehyde for fixation is glutaraldehyde. • Glutaraldehyde fix proteins very rapidly. • Glutaraldehyde may not penetrate thicker tissue specimens as effectively as formaldehyde. • Glutaraldehyde may offer a more rigid or tightly linked fixation.
  4. 4. • In order to demonstrate lipids,frozen sections are commonly used. used to preserve phospholipids. • For preservation of lipids in cryostat sections fixative should contain • For this purpose we use the • Fixation is over 3 days at room temperature.
  5. 5. • Alcoholic fixatives are used for glycogen fixation. are • Fixatives for ultrasturctural preservation of dextrans and glycogen is • • • • • It is used by making stock solutions of Formaldehyde Glutaraldehyde Osmium tetraoxide Lead citrate
  6. 6. • Biogenic amines can be demonstrated in tissues using a variety of techniques. • In this reaction potassium dichromateformaldehyde is used. Formaldehyde fixation of the adrenal medulla produced fluorescence of cells which contained biogenic amines or carnoy fixed paraffin section For histamines • Primary biogenic amines are well preserved by
  7. 7. • Fixatives choosen for nucleic acids must depend upon subsequent methods which are to be employed in analysis of tissue. –based fixatives (used but mostly avoided) – (most widely used) • It is to be used then the hydrolysis time varies with the fixative.
  8. 8. • For accurate demonstration of water soluble substances,non-aqueous fixatives are used. For example, Urates in gout is a satisfactory fixative For steriods.
  9. 9. Target Fixatives of choice Fixatives of avoided proteins Natural buffered formalin, paraldehyde Osmium tetroxide lipids Frozen sections Chemical fixative Nucleic acid Alcoholic fixative Aldehyde fixative Glycogen Alcoholic based fixatives Osmium tetroxide

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