What is the purpose of using propylene oxide in tissue processing?

Propylene oxide serves primarily as a dehydrating agent in the process of tissue processing for histopathology. The primary purpose of dehydration is to remove water from the tissues, as most embedding media used in histology, such as paraffin, are hydrophobic and do not mix with water. Propylene oxide is advantageous because it effectively removes water from tissue samples without causing undue damage or distortion to the cellular architecture.

As tissues are prepared for embedding, sequential dehydration is essential, typically involving the use of increasing concentrations of alcohol, ultimately followed by a clearing agent, such as propylene oxide. This intermediary step helps facilitate the infiltration of the embedding medium. By adequately dehydrating the tissue, propylene oxide ensures that the structural integrity and morphology are preserved, enabling accurate microscopic examination later.

The context of other choices helps clarify the function of propylene oxide; while hardening refers to the process of making tissues more resilient during embedding, embedding itself is the final step where tissues are infiltrated with resin or paraffin. Staining processes, on the other hand, are employed after embedding to visualize specific cellular components and are not related to the dehydration step.