Introduction Flashcards
What is histology ?
The study of tissues
Why do we need to study histology ?
- important in understanding the internal structure of tissues and organs
- relation to cell biology
- closely connected to pathology
How do we calculate overall microscope magnification ?
Objective lens magnification x eyepiece magnification
What are the advantages of electron microscopes ?
- high resolution
- high magnification
What are the disadvantages of using electron microscopes ?
- magnification is too high for most needs
- very expensive to buy and use
- the specimen is difficult to prepare
- can only look at tiny specimens
How is the specimen prepared for use in electron microscopes ?
1) it is first placed in a fixation chemical - this helps to preserve the tissue and maintain its structure
2) the specimen is then infiltrated with a supportive, strengthening material (such as paraffin wax) - this allows the specimen to be sectioned without being crushed
3) the specimen is then sectioned so that light can pass through - for electron microscopes ~ 50 nm
Which chemical is used to fix the tissue sample ?
The fixative used is formaldehyde - it cross links proteins which forms a stable network and this prevents prevents tissue breakdown
How is tissue strengthening carried out ?
1) water is removed from the tissue using an alcohol dilution series
2) the alcohol is then removed from the tissue by immersing it in xylene - this is known as clearing
3) the xylene is then replaced with melted wax
4) the sample is then placed in fresh wax in a mould and left to cool
How is sectioning carried out ?
The microtome of the arm of the sectioning machine moves up and down so the steel blade cuts thin ribbons of sections
Why is staining required ?
In sectioned biological material, there is little to no contrast
How is the specimen stained ?
1) the wax is removed
2) the specimen is then rehydrated through an alcohol dilution series
3) the specimen is stained
4) the specimen is washed
5) the specimen is then dehydrated through an alcohol dilution series
6) the specimen is then cleared in xylene
7) it is then mounted under a coverslip in a transparent adhesive mountant
What are the most common dyes ?
Haematoxylin - a basic dye and so reacts with acids (nuclei stain blue)
Eosin - an acidic dye and so reacts with bases (cytoplasm etc stain pink)
They are commonly used as a pair
Define tissue
A collection of cells and extracellular materials specialised for a particular function
What are the 4 basic tissues ?
• epithelium - linings, coverings and derivatives
• connective tissue - connecting, binding, support and space filling
• muscle - movement
• nerve - communication
Define organ
A distinct functional unit formed from 2 or more tissues
