Week 3 Flashcards
What is histopathology
Identification of diseases in tissues
The main steps include: Fixation, dissection, process , stain and microscopic exam
Name the 2 types of fixatives with examples
Coagulants: Removes lipids which dehydrates the tissue e.g Alcohol / Acetone.. used in cytology
Non-coagulants: Forms cross-links to preserve the tissue.. e.g Formaledhyde, used in histology and e- microscopy
Osmium tetroxide
For EM, preserves structure but is toxic and expensive
Tissue processing
The treatment of tissues by fluids leading to impregnation by solidifiable embedding medium
Microtomy
Machine that cuts thin strips for microscopic examination
Compare EM scanning and EM Transmission
EMS: E- beams over surface, scans large samples, tissue placed in aluminium, 50x mil mah
EMT: E- beams through, scans thin samples. tissue placed on copper, mag 2x mill
What is the primary goal of fixation?
To preserve tissue structure by preventing enzymatic degradation and bacterial growth.
What is the most commonly used fixative for light microscopy?
10% neutral buffered formalin (formaldehyde solution).
Which fixative is commonly used for electron microscopy?
Glutaraldehyde.
What happens if tissue is not properly fixed?
It may undergo autolysis or putrefaction, leading to structural damage.
The 3 steps in tissue processing
Dehydration, clearing and embedding
Why is dehydration necessary before embedding?
To remove all water, which is incompatible with embedding media like paraffin.
What solvents are typically used for dehydration?
Ethanol
What is the purpose of the clearing step?
To remove alcohol and make tissue receptive to infiltration by paraffin wax.
Which chemical is commonly used for clearing?
Xylene.
Why is embedding necessary?
It provides a firm medium for sectioning thin tissue slices.
What material is used for embedding in LM?
Paraffin wax.
What tool is used for sectioning paraffin-embedded tissue?
A microtome.
Why is staining necessary in histology?
biological tissues are transparent and require staining for contrast.
What does hematoxylin stain and what color does it produce?
Nuclei and other acidic structures; blue to purple
Basic dye
What does eosin stain and what color does it produce?
Cytoplasm and extracellular matrix; pink.
Acidic dye
What is immunohistochemistry (IHC)?
A method that uses antibodies to detect specific antigens in tissues.
What are histological artifacts?
Distortions or errors in tissue appearance caused by processing.
Give an example of a common artifact.
Shrinkage, folding, or tearing of tissue sections.
