HISTOLOGIC TECHNIQUES Flashcards
Define a biopsy
Removal and usually microscopic examination of tissue from the living body, performed to establish precise diagnosis
mention 6 types of biopsy
- Aspiration biopsy
- Brush biopsy
- Core needle biopsy
- Excissional biopsy
- Incissional biopsy
- Shave biopsy
What happens in tissue accesioning
- New specimens are registered in a book
- Specimens usually come in formalin faxative
- Specimens are macroscopically examined
How is a tissue examined macroscopically
~ Appearance is described and weighed
~suspicious portions are selected and cut
What is the purpose of tissue processing
means handling of tissue specimen until it is ready for staining
what steps are caried out during tissue processing
- Fixation
- Dehydration
- Clearing
- Infiltration
explain embedding as a step in tissue handling
Embedding: This step involves placing tissue samples into a mold with a liquid embedding medium (such as paraffin wax) that will solidify. Embedding helps prepare the tissue for sectioning
mention the tissue handling steps
Embedding
Blocking
Trimming
Sectioning
explain blocking as a step in tissue handling
Blocking: After embedding, the tissue block is trimmed to a specific size and shape. This process ensures that the tissue is properly oriented for sectioning.
Explain trimming as a step i tissue handling
Trimming: Trimming refers to removing excess embedding medium from around the tissue block. It ensures that only the tissue of interest remains for sectioning
Explain sectioning as a step in tissue handling
Sectioning: In this step, thin slices (sections) of the tissue block are cut using a microtome. These sections are then mounted on slides for further analysis (e.g., staining, microscopy).
explain 5 purposes/aim of fixation
- to prevent decomposition
~Decomposition may be due to O2 and essential metabolite deprivation, deprivation of blood supply and accumulation of by-product of metabolism.
~The fixative denature or precipitate proteins which form sponge or meshwork that tend to hold other cells constituents. - It prevents cellular autolysis
a. the fixative inactivates the lysosomal enzyme
b. The fixative chemically alters the cell components so that they become resistant to enzyme degradation. - It prevents putrefaction
~Fixation seems to protect the tissue from microbial damage - protects the tissue from damage during subsquent preparative operations. e.g dehydration, embedinng, sectioning and mounting
- Insolubilisation of tissue
Fixation renders insoluble certain tissue components that woud otherwise leach out during subsquent handling.e.g lipids.
However, no one fixative is capable of insolubilising all tissue components.
Therefore, the success of examining a particular component lies in the proper selection of fixative to use
mention the factors affecting fixation
- Buffering and PH
- Penetration
- Temperature
- Concentration of fixative
- Volume of fixative
factors retarding (delay) fixation
1.Size and thickness of tissue specimen
2. Presence of mucus-preventing complete penetration of fixative. .Excess mucus can be washed away with normal saline.
3. Presence of fat
4. Presence of blood
5. Cold temperature
How does buffering and PH affect fixation
Fixation is best carried out close to neutral pH.
Hypoxia of tissue lowers the tissue pH, as such, there should be a buffering capacity to prevent excess acidity.
Acidity favors formation of formalin, lead to formation of black pigment in tissue.
Common buffers; phosphates, bicarbonates, cocodylates and veronal.
The buffer must not react with the fixative, inhibit enzymes or react with incubation medium.
How does penetration affect fixation
For proper fixation, the fixative needs to reach all parts of the tissue sample. Inadequate penetration results in uneven fixation, with some areas well-preserved and others poorly fixed. This can lead to artifacts and difficulty interpreting the tissue structure under a microscope.
How does temperature affect fixation
Fixation of most surgical specimens is at room temperature.
For electron microscopy and some histochemistry, the temperature range is 0-4oC
As a rule, cold temperatures retards fixation and mderate heat accerates fixation but also hastens autolytic changes and enzyme destruction
How does concentration of fixative affect fixation
A certain level of fixative concentration is necessary for effective fixation. The fixative molecules need to be present in sufficient numbers to react with and stabilize the molecules within the tissue sample. If the concentration is too low, there might not be enough fixative molecules to properly cross-link and preserve the tissue structures.
How does volume of fixative affect fixation
There should be a 10-20:1 ratio of fixative to tissue volume.
what are the principles and precations in handling and fixation of specimens
1 . Both autopsy and surgical material should fixed as soon as possible.
2. All tissues should be properly labelled and identified.
3. Avoid put refrigerated tissues at 0oC to avoid ice formations
4. Tissues should not be more than 5mm thick.
5. Required time of fixation should not be exceeded to avoid hardening and brittleness of tissue.
6. There must be adquate supply of fixative at all times
7. Avoid drying of specimens to avoid shrinkage and distortion of cellular details.
8. Solid organs should be injected with as well as emersed in enough fixative to ensure enough fixation.
9. Hollow organs should be packed with cotton soaked in fixative or completely opened before being emersed in adequate fixative.
10. Air-filled organs like lungs float on the fixative. To avoid this, the organ may be covered with several layers of guaze to keep it undersurface.
11. Dense tissues are poorly penetrated hence require longer fixation.
