Intro To Histology Flashcards
What is histology?
The microscopic study of normal cells and tissues
What is disease typically associated with in relation to tissue structure and function?
Usually associated with disruption of normal tissue structure and function
That is pathology?
The microscopic study of disease cells and tissues
What is dysplasia of squamous cells?
Refers to abnormalities in squamous epithelium, the epithelium being the layer of cells that lines the cavity or surface in the body
What are examples of physical and chemical insults that induce alterations in tissue architecture?
- Infection
- Extreme heat/cold
- Cuts or fractures
- Poison/drugs
- Genetic and congenital changes
- Aging, wear and tear
- Cancer
What is required to visualise tissue structure?
Microscopes as cells are too small to see by the naked eye
What 2 microscopes are used to look at tissue samples?
- Light microscope
- Electron microscope
What does a light microscope reveal of the tissue?
Basic cellular structure
What does an electron microscope reveal of the tissue?
Ultrastructure - structures only able to see through electron microscope
Which microscope is most commonly used for routine histopathology?
Light microscope
What are the 7 steps for making thin tissue samples for viewing?
- Specimen collection
- Fixation
- Dehydration
- Embedding
- Sectioning
- Staining
- Viewing
What are the 3 types of biopsy?
- Incision or punch biopsy
- Needle biopsy
- Endoscopic biopsy
What is an incision or punch biopsy of?
Skin/oral surfaces
What is a needle biopsy of?
Organs or lumps below the skin
What is an endoscopic biopsy?
Flexible tube with light and camera. Cutting tools can be used to collect tissue specimens
What imaging techniques are often used to guide biopsy?
X-ray, MRI
What does fixation of tissue do?
- Preserves the structural arrangement between cells and extracellular components
- Terminates all biochemical reactions and so prevents tissue decomposition
What are 2 common fixatives?
- Formaldehyde
- Glutaraldehyde
What is dehydration of tissue to produce a tissue sample?
- Water is removed from tissue using a series of graded alcohols
- Water is removed gradually to prevent distortion
Why does tissue need to be dehydrated for tissue sampling?
Since paraffin in immiscible with water, the main constituent of tissue, Samples need to be dehydrated by progressively more concentrated ethanol baths. This if followed by a clearing agent, usually xylene, to remove the ethanol. Finally molten paraffin wax infiltrates the sample and replaces the xylene
What materials are most commonly used for embedding?
- Resins
- Paraffin wax
Why does tissues for sample need to be embedded?
- Thin tissue sections are required for microscopy BUT most tissues are delicate and easily distorted, so tissues must be supported to allow thin sections to be cut
Paraffin is not compatible with alcohol, so what is alcohol replaced with to allow embedding to occur?
Xylene
What must the characteristics of tissue sections be?
- Thin and flat
- Ideally a single layer of cells
- Should be transparent
What is a microtome?
- What embedded specimens are sectioned using
- A tool used to cut extremely thin slices of material
What can tissue sectioning in different areas of the tissue cause?
Can make a big difference to tissue architecture
Why do most cells need some sort of staining?
- Most of them are colourless and transparent
- Staining makes cells and their components more visible
- Allows the identifications of different cell and tissue features
What is the composition of most LM stains?
- Aqueous
Some stains for tissue examination are not compatible with paraffin, what needs to be done to fix this?
- Reversal of dehydration steps to remove paraffin wax and replace with water
What is the most commonly used stain?
Haematoxylin and Eosin (H&E)
What is haematoxylin?
A basic dye, which stains acidic structures (such as nucleic acids) BLUE/PURPLE
What is eosin?
An acidic dye that stains basic structures (such as cytoplasmic proteins) RED or PINK
What does periodic acid-Schiff reaction stain?
Complex carbohydrates MAGENTA (such as mucins, produced by goblet cells, brush borders and basement membranes)
What does Masson trichrome stain?
- Stains connective tissues
- Nuclei and other basophilic structures stain BLUE
- Collagen stains GREEN/BLUE
- Cytoplasm, muscle, red blood cells ad keratin stain RED
What is immunohistochemistry?
Refers to the process of detecting antigens in cells of a tissue section via antigen reveal. This is carried out by exploiting the principle of antibodies binding specifically to antigens in biological tissues
How do you make permanent mounts of tissue samples?
- Stained sections are dehydrated once again to replace water with xylene
- Mounting medium and a coverslip seal to protect sections
