MLT GlobeHistopathology: Lab safety, equipment & museum
20 Histopathology MCQs on Lab safety, equipment & museum with answers and explanations.
Disposable latex or nitrile gloves mainly protect lab staff from:
Gloves are a barrier to fluid contact; they do not resist sharps, and aerosols need respiratory protection or a safety cabinet.
What is the main safety hazard of picric acid?
Dry picric acid is shock-sensitive and explosive, so it is stored moist with water.
Which step is essential when picking sections up on slides?
Correct labelling links each slide to its patient and block; mislabelling can cause a wrong diagnosis.
Which microscope gives a three-dimensional view of a specimen for grossing or dissection?
Stereo microscopes use two optical paths, one per eye, giving depth perception at low magnification.
The 'high-dry' objective on a standard light microscope has what magnification?
The 40× objective is the highest used without immersion oil. The 100× objective requires oil; 10× is low power.
To pull a paraffin block from the archive, a technician should search by:
Blocks and slides are filed by unique accession number, which links to the patient record. Names and bed numbers are not unique or durable identifiers.
Kaiserling solutions are used for:
Kaiserling fixatives and preservatives retain the natural colour of gross specimens displayed in pathology museums.
Unstained living cells in culture can be viewed with good contrast using:
Phase contrast converts small differences in refractive index into differences in brightness, so live cells can be seen without staining. TEM requires fixed, sectioned material.
Which microscopic technique cannot be used to examine living cells?
TEM needs a vacuum and fixed, ultrathin, heavy-metal-stained sections, so cells must be dead. Phase contrast, DIC and fluorescence can all image live cells.
A temperature log reads 38.2 °F (about 3.4 °C). This reading is typical of which laboratory equipment?
38.2 °F converts to about 3.4 °C, within the 2–8 °C refrigerator range. Freezers run below 0 °C and incubators near 37 °C.
Kaiserling solutions used for museum specimens preserve natural colour. Their fixing agent is:
Kaiserling fixatives are formalin-based with potassium salts; picric acid stains tissue yellow.
A slide that focuses at 10× cannot be brought into focus with the 40× objective. The most likely cause is:
With the coverslip facing down, the slide thickness exceeds the short working distance of the 40× objective. Staining or smear thickness affects image quality but not the ability to focus.
Which piece of routine histology equipment does NOT depend on a controlled temperature to function?
Embedding centres, processors and flotation baths all hold wax or water at set temperatures. A standard rotary microtome is a mechanical cutting device used at room temperature.
In a phase contrast microscope, the annular diaphragm in the condenser must be aligned with which component?
Light passing through the condenser annulus must fall on the matching phase ring in the objective to create contrast. Prisms and polarizers belong to DIC and polarization microscopy.
Under polarized light, which structure appears dark because it is isotropic (non-birefringent)?
The I-band is isotropic and the A-band anisotropic, hence their names. Collagen and bone lamellae are birefringent.
In a tissue autoradiograph, the developed silver grains over labelled cells are best visualized as bright points against a dark background using which microscopy?
Dark-field illumination makes the light-scattering silver grains appear bright, so even small numbers are easily counted. Polarizing microscopy is for birefringent material such as crystals or amyloid.
Which clearing agent is most associated with skin sensitization after repeated use?
D-limonene clearants oxidize to allergenic compounds and can cause contact sensitization with prolonged exposure. Xylene is mainly a neurotoxic and irritant hazard.
Under the OSHA formaldehyde standard, the 8-hour time-weighted average permissible exposure limit is:
OSHA sets the 8-h TWA PEL at 0.75 ppm; 0.5 ppm is the action level and 2 ppm the 15-minute short-term limit.
For a cryostat in daily use, CAP accreditation expects routine decontamination at a defined interval; the commonly applied minimum is:
Cryostats must be decontaminated at defined intervals (commonly at least weekly for daily use) and after known infectious cases, since freezing does not inactivate pathogens such as TB.
A section stained mainly blue is photographed in bright field. Which colour filter will give the greatest contrast?
A filter of the complementary colour is absorbed by the stained structures, making them appear dark against a bright background. A blue filter would make blue structures fade.