3. • 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.

4. •
•
•
•
•
•
•
Which are to be fixed are following
Proteins
Lipids
Carbohydrates
Biogenic amines
Nucleic acids
Water and lipid soluble substances

5. • 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.

6. • 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.

8. • 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

9. • 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

10. • 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.

11. • For accurate demonstration of water soluble
substances,non-aqueous fixatives are used.
For example, Urates in gout
is a satisfactory fixative
For steriods.

12. 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