S1 Examining Cells Flashcards
What is a biopsy?
Taking a tissue sample from a person to examine it histologically
What are the 7 steps to prepare a sample for viewing under a microscope?
- Obtaining the specimen
- Fixation
- Washing, dehydration and embedding
- Cutting
- Placing on microscope slide
- Staining
- Mounting
How do you obtain a specimen?
Use surgery, venepuncture (for blood smears), scraping method (curettes, scalpel) or sharp needles (needle biopsy, pipette)
How do you fix a cell/tissue sample?
Fix using formalin (formaldehyde and NaCl - isotonic so better cell penetration)
Why do you fix a cell/tissue sample?
To prevent decay of the sample (as no longer has immune responses). It also removes water so stiffens the sample.
What are fixation artefacts?
If sample is left in fixative for too long, shrinkage occurs due to dehydration
How do you embed a tissue sample?
)Use paraffin wax (xylol or toluol)
Why do you embed a tissue sample?
To allow you to cut thin sections
What is a disadvantage of embedding with paraffin wax?
The paraffin strips lipophilic molecules
What is a microtome?
Used to cut thin sections of a tissue sample.
It has a steel blade or diamond knife (used in electron microscopes)
What is coated on the microscope slide to allow better adhesion of the section to the slide?
A sticky substance like albumin
Why do you place the sample in a water bath after cutting?
To allow the sample to stretch and reduce any cutting artefacts
What is the most used stain in histology?
Haematoxylin and Eosin (H&E)
What does H&E stain and why?
H - stains nuclei blue (as H is basic)
E - stains cytoplasm and ECM (as E is acidic)
When stained with both, sample appears purple
Do you stain with H or E first?
H, then wash, then stain with E
What is the sample mounted on before viewing with a microscope?
A non-aqueous medium
What reagent/dye do you use to detect sugars?
Periodic acid-Schiff reagent
What is considered the most sensitive and specific histological technique?
Immunohistochemistry as antibodies/antigens and enzymes are so specific
What microscope do you use alongside immunohistochemistry?
Confocal microscope
Why would you use a frozen section?
- Quicker
2. If the tissue has a less robust structure
What are the SEM, TEM and light microscope best used for viewing?
SEM - examining cell surfaces
TEM - examining intracellular structures and organelles
Light microscope - examining the general structure of a cell
What is the cytoskeleton made up of?
Microfilaments, intermediate filaments and microtubules
What are microfilaments used for?
Contain actin, contract/relax and change the cell shape
What are intermediate filaments used for?
They aren’t dynamic, make up desmosomes
What are microtubules used for?
Moving structures e.g vesicles around a cell using proteins called dynein and kinesin
What occurs at the nucleolus?
Ribosomal RNA synthesis
