Fixation
What is the primary purpose of tissue fixation in histological studies?
To preserve tissue structure by preventing autolysis and decomposition.
What are the three steps in tissue processing?
Dehydration, clearing, and infiltration.
What is the primary purpose of tissue embedding in histological studies?
To provide structural support to the tissue for microtomy by surrounding it with a solid infiltration medium like paraffin wax.
What is the primary purpose of microtomy?
To cut thin, precise sections of embedded tissue samples for microscopic examination.
What is the purpose of using a cryostat in histological studies?
To section frozen tissues for rapid diagnostic procedures or specialized staining techniques.
Which of the following is the most commonly used fixative in histological tissue processing?
10% NBF
What does the term 'miscible' mean in a scientific context?
The ability of two substances to mix completely without separating.
Why is correct orientation important when embedding tissue samples?
It ensures that the tissue is sectioned in the correct plane to highlight the required diagnostic features.
Name 3 mechanical components of the microtome and their purpose.
Blade holder, tissue block holder, and coarse feed wheel (and more!)
What are the key differences between microtomy and cryostat sectioning?
Microtomy sections paraffin-embedded tissues, while cryostat sections frozen tissues at very low temperatures.
What chemical mechanism allows formalin function as a fixative in tissue preservation?
It cross-links proteins by forming methylene bridges between amino groups, stabilizing tissue structure.
What is the primary role of clearing reagents in the process of preparing tissue samples for histological analysis?
To replace alcohol in the tissue and make it compatible with the infiltration medium (usually paraffin).
Why do hard tissues like bone need to be embedded at an angle?
To reduce the resistance during sectioning and create smooth sections
Describe the steps you should take if you encounter tissue shredding or "moth-holing" while sectioning a sample.
Ensure the blade is sharp and free of any debris or residue. A dull or damaged blade often causes tissue shredding. Don't face aggressively.
What is a Moh's procedure?
Mohs Procedure (or Mohs Micrographic Surgery) is a specialized surgical technique used to treat certain types of skin cancer, such as basal cell carcinoma and squamous cell carcinoma.
Name 3 factors that impact tissue fixation quality.
Tissue size, fixative penetration, and fixation time.
Match the following properties of ethanol with 'Advantage' or 'Disadvantage':
Absorbs water readily.
Prolonged exposure to 100% ethanol can cause tissue shrinkage and hardening.
Ethanol >70% mixed with formalin can result in a phosphate salt precipitate.
Advantage
Disadvantage
Disadvantage
Soft, mushy centers after embedding indicate sections were too thick at the grossing station. What is your next step?
Re-trim the block to expose thinner sections of the tissue and reprocess if necessary.
Describe steps to take if tissue has knife marks or repetitive lines in the sections.
Shift the blade or replace the blade.
Name one common issue encountered during cryostat sectioning and a way to resolve it.
A: Issue: Tissue sections curl.
Solution: Adjust the anti-roll plate or cool the tissue more thoroughly.
Which of these factors are disadvantages to using formalin in the lab?
Toxicity, potential to cause over-hardening, its ability to form paraformaldehyde crystals over time, and ability to form a formalin pigment when exposed to the wrong pH.
Describe two methods commonly used to evaluate the adequacy of tissue processing in histological studies .
1) Visual inspection of tissue consistency.
2) Performing a test H&E stain to check nuclear and cytoplasmic detail.
Why do we need to cool blocks quickly after embedding?
To reduce the wax crystal size and allow for smoother sectioning.
When you attempt to section the embedded tissue using a microtome, you notice that the sections are tearing and not coming out as smooth ribbons.
Identify two possible causes for tearing tissue sections.
Cause 1: Blade is dull. Action: Replace the blade with a new one.
Cause 2: Tissue is too warm or improperly embedded. Action: Cool the block in an ice tray before sectioning.
Describe how tissue freezing quality can impact cryostat sectioning results.
Poor freezing can cause ice crystal formation, leading to distorted or damaged sections.