A microtome is a precision medical laboratory instrument used to cut tissue into extremely thin slices for viewing under a microscope. These slices allow pathologists and researchers to see cell structure, tissue organization, and signs of disease. Microtomes are essential in hospitals, biopsy labs, and research centers because accurate diagnosis often depends on clear tissue sections.
Without thin, even slices, light cannot pass through the sample well enough to reveal microscopic detail.
In a rotary microtome, a tissue sample is usually embedded in paraffin wax, mounted in a specimen holder, and moved toward a very sharp blade in tiny measured steps. Each turn of the handwheel advances the block so the blade shaves off a thin section, often only a few micrometers thick. The sections may form a ribbon as they curl away from the blade, then they are placed on a glass slide and stained.
The quality of the final microscope image depends on blade sharpness, cutting thickness, tissue preparation, and careful handling.
Key Facts
- Typical histology section thickness = 3 to 10 micrometers
- 1 micrometer = 0.001 millimeter
- Section thickness is controlled by the microtome feed mechanism
- Number of sections = block advance distance / section thickness
- Clear tissue sections require a sharp blade and stable specimen holder
- Paraffin embedding supports soft tissue so it can be sliced cleanly
Vocabulary
- Microtome
- A microtome is a laboratory instrument that cuts tissue into very thin sections for microscope study.
- Tissue block
- A tissue block is a prepared sample, often embedded in wax, that is held in the microtome for cutting.
- Section
- A section is a thin slice of tissue cut from a tissue block and placed on a slide for viewing.
- Paraffin embedding
- Paraffin embedding is the process of surrounding tissue with wax to support it during thin slicing.
- Rotary microtome
- A rotary microtome is a type of microtome that uses a handwheel to move the specimen past a fixed blade in controlled steps.
Common Mistakes to Avoid
- Confusing micrometers with millimeters is wrong because a micrometer is 1000 times smaller than a millimeter, which changes section thickness calculations greatly.
- Using a dull blade is wrong because it can tear, compress, or chatter the tissue, making cells harder to identify under the microscope.
- Assuming thicker sections always give better images is wrong because overly thick tissue blocks light and causes overlapping cell details.
- Skipping proper tissue support is wrong because soft tissue can deform during cutting unless it is fixed, embedded, frozen, or otherwise stabilized.
Practice Questions
- 1 A microtome is set to cut sections 5 micrometers thick. How many sections can be cut from 0.50 millimeter of tissue block advance?
- 2 A ribbon contains 12 tissue sections, and each section is 4 micrometers thick. What total thickness of tissue was removed in micrometers and in millimeters?
- 3 A student sees torn, uneven tissue sections coming from a rotary microtome. Explain two possible causes and how each one could be corrected.