3. Principles of the methods of cytological and histological examination

Question 1

What is the first step called? Is it done by one chemical or a mixture of chemicals? Why is it done? Name 4 reasons? What is the most commonly used fixative?

Answer 1

The first step is called fixation.

It can be done by one or a mixture Of chemicals.

It is done to preserve the structure of the tissue.

1. Terminate cell metabolism
2. Prevent enzymatic self degradation called autolysis.
3. To remove pathogenic microorganisms.
4. Harden the tissue.

The most commonly used fixative is called formalin.

Question 2

What is the second step? In what is it embedded and why? Explain the process of it? What solvents are used normally. What’s is the machine that slices the material called?

Answer 2

The second step is embedding.

It’s embedded in paraffin to make it easier to slice.

It’s washed. Its dehydrated in alcohol. Then it’s cleared. Then we need to use xylol or tulol to remove the alcohol before the infiltration of the specimen with melted paraffin. Then it’s dried and hardened and ready for it to be sliced by a microtome.

Question 3

What is the third and last step? Why do we need to stain it? How do we dissolve the paraffin? How do we rehydrate it? What are the slides stained with and in what? What’s the next step before the second dying? What’s the last dye and how is it done?

Answer 3

The last step is staining.

The slide is colourless so we need to stain it in order to examine it with a microscope.

The paraffin needs to be dissolved with xylol or tulol. We then need to rehydrate it with a series of alcohol concentrations.

The slides are then stained with hematoxylin in water. It’s then rehydrated in alcohol again. The last step is to dye it in eosin in alcohol.