MLT GlobeHistopathology: Tissue processing & embedding
39 Histopathology MCQs on Tissue processing & embedding with answers and explanations.
Which reagent is used after dehydration to make tissue miscible with paraffin wax?
Xylene is a clearing agent: it replaces alcohol and dissolves wax. Ethanol dehydrates but does not mix with paraffin.
Tissue has just been through ascending grades of alcohol. What is the next processing step?
Alcohol and paraffin do not mix, so a clearing agent is needed first; impregnation and embedding follow clearing.
Which reagent removes water from tissue during processing?
Graded ethanol dehydrates; xylene clears, paraffin impregnates and eosin is a stain.
Which reagent does NOT act as a clearing agent in tissue processing?
Clearing agents are miscible with alcohol and paraffin; acetic acid is a fixative component, not a clearant.
Which substance forms the supporting block from which sections are cut?
Paraffin wax is the routine embedding medium; ethanol and acetone dehydrate and formalin fixes.
What is the main purpose of infiltrating tissue with molten paraffin?
Wax fills the tissue spaces and hardens, so the block can be cut into thin sections without crumbling.
The most essential property of a clearing agent is that it:
Clearing must bridge alcohol and wax; low toxicity and cost are desirable but secondary.
Which statement about paraffin wax as an embedding medium is FALSE?
Paraffin is solid and firm at room temperature, giving block support; softness would prevent sectioning.
Routine paraffin embedding wax typically has a melting point of about:
Most histology wax melts near 56–58 °C; much higher melting waxes are not used routinely and would overheat tissue.
Modern enclosed tissue processors speed up reagent penetration mainly by using:
Warming, vacuum and pressure cycles, and agitation all hasten exchange of fluids and wax infiltration.
An automated tissue processor moves fixed tissue through reagents in which order?
Tissue is dehydrated in graded alcohols, cleared in a wax-miscible solvent such as xylene, then infiltrated with molten paraffin. Wax cannot enter tissue containing water or alcohol.
Enclosing processed tissue in a medium such as paraffin wax, which then solidifies into a block, is called:
Embedding orients the infiltrated tissue in a mould of wax (or agar, resin, gelatin) that hardens to allow sectioning.
During paraffin processing, what is xylene's role?
Wax is not miscible with alcohol, so xylene (a clearing agent) is used between dehydration and infiltration. Alcohol removes water; mountants attach coverslips.
Xylene, the classic clearing agent, belongs to which chemical group?
Xylene is dimethylbenzene, a benzene-ring (aromatic) hydrocarbon. Aliphatic clearing agents are the straight-chain xylene substitutes.
When several skin fragments are placed in one mould, how should their epidermal surfaces be oriented?
Aligning all epidermal surfaces the same way lets every piece be cut in the same plane and direction, giving uniform sections and avoiding compression differences.
Tissue is first infiltrated with celloidin and then embedded in paraffin. This approach is called:
Double embedding combines a supporting medium such as celloidin or agar with paraffin, useful for hard or friable tissues.
Delicate specimens on a closed tissue processor should be dehydrated using:
Gradual transfer from lower to higher alcohol concentrations minimizes shrinkage and distortion.
Which factor mainly determines how long a tissue needs for complete paraffin impregnation?
Large, thick or dense tissues (e.g. bone, fatty tissue) need longer wax infiltration; wax melting point and vacuum also matter.
Tissue left too long in which clearing agent is most likely to become hard and brittle?
Prolonged xylene hardens tissue and makes sectioning difficult; chloroform and cedarwood oil cause less hardening.
Why is tissue dehydrated through graded alcohols rather than placed straight into absolute ethanol?
Gradual exchange of water for alcohol limits osmotic distortion; ethanol mixes freely with water.