a. why different grades of alcohol are used for dehydration in staining procedure?
Answers
Answer:
Dehydration is simply the removal of water from aqueous-fixed tissue. Since most fixatives are aqueous, this step is necessary to prepare the tissue for embedding in non-aqueous media like paraffin. Alcohols are most commonly used in the laboratory for tissue dehydration, since they are miscible with aqueous fixatives like 10% formalin. In this step, the alcohol penetrates tissue quickly and the water is replaced with alcohol. Since alcohols act rapidly and may shrink and harden tissue too much, care must be taken when calculating the amount of time needed in the dehydration step. This step is performed at room temperature. Ethyl alcohol and isopropyl alcohol are used most often, with methanol and butanol being used to some degree in special techniques. Since most alcohols (with the exception of isopropyl alcohol) and paraffin are NOT miscible, another step, known as clearing, is introduced.
Explanation:
Dehydration of tissues is the important process because of the paraffin, in which the tissues are embedded, is not miscible with water and does not penetrate the tissue effectively. Hence water in the tissue should be removed before embedding; this process is called as dehydration. Tissues are generally soft after fixation and thus for satisfactory staining and the right degree of hardening, the tissue is treated with the dehydrating agent.
THE IDEAL TECHNIQUE OF DEHYDRATION
Water is extracted from the tissues by passing them through the graded alcohol as 70%, 80%, 90% and then Absolute alcohol. This technique prevents the mechanical damage to delicate intracellular structures, which may occur due to the rapid passage of water from the cells to the dehydrating medium.