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
