Enhancement Questions
Draw the set-up for dehydration and clearing.
1. Give the importance of:
a. Dehydration
Dehydration is important in tissue processing because it will remove the water present in the
specimen which is not miscible to the paraffin that will be used on the later tissue processing steps
in embedding. In order for the paraffin to penetrate the tissue completely and effectively, the water
that is present should be removed first which will be done in the dehydration process using
dehydrating agents such as alcohol.
b. Clearing
Clearing will make the components of the tissue easier to see because the high refractive index
of most clearing agents makes the specimen transparent. Tissue fats are also removed in this
step which can hinder in the paraffin infiltration step.
2. Why do you start from lower to higher concentration of alcohol during dehydration?
We need to dehydrate the specimen in ascending grades of alcohol to ensure complete
penetration of alcohol into the specimen. If the tissue is immersed in a very high concentration as
the initial concentration, then the tissue will only harden on the surface and the deeper parts will
not be completely penetrated. Also, we need to be careful in adding reagents in the specimen
since most dehydrating agents can cause shrinkage and destruction of cellular components so in
order to avoid violent osmotic changes of the tissue, alcohol concentration is added in increasing
manner.
Draw the set-up for dehydration and clearing.
1. Give the importance of:
a. Dehydration
Dehydration is important in tissue processing because it will remove the water present in the
specimen which is not miscible to the paraffin that will be used on the later tissue processing steps
in embedding. In order for the paraffin to penetrate the tissue completely and effectively, the water
that is present should be removed first which will be done in the dehydration process using
dehydrating agents such as alcohol.
b. Clearing
Clearing will make the components of the tissue easier to see because the high refractive index
of most clearing agents makes the specimen transparent. Tissue fats are also removed in this
step which can hinder in the paraffin infiltration step.
2. Why do you start from lower to higher concentration of alcohol during dehydration?
We need to dehydrate the specimen in ascending grades of alcohol to ensure complete
penetration of alcohol into the specimen. If the tissue is immersed in a very high concentration as
the initial concentration, then the tissue will only harden on the surface and the deeper parts will
not be completely penetrated. Also, we need to be careful in adding reagents in the specimen
since most dehydrating agents can cause shrinkage and destruction of cellular components so in
order to avoid violent osmotic changes of the tissue, alcohol concentration is added in increasing
manner.
