Histology and cytology
What is fixation?
Stabilises the proteins, nucleic acids, and mucopolysaccharides in the tissue sample and stops enzyme autolysis and bacterial putrefaction.
What are the two classifications of fixatives?
- Cross linking fixatives (Aldehydes)
- Precipitating fixatives (Alcohols)
What are the different types fo fixative?
- Single chemicals such as ethanol and formaldehyde
- Compounds such as Carnoy's fluids (60% ethanol, 30% chloroform, 10% acetic acid)
What factors effect fixation?
- Volume of tissue
What are the steps is tissue processing?
- Wax infiltration
What are the purposes of Dehydration in histology?
To remove fixative and water from tissue and replace them with dehydrating fluids. The specimen is dehydrated through an ethanal series to prevent tissue distortion.
What are the purposes of clearing in histology?
Replacing the dehydrating fluid that is miscible with the embedding medium, the clearing agent depends on the tissue, and the conditions in the net step.
What are examples of clearing agents?
- Zylene, Toluene, Chloroform, Benzene and Petrol.
What is the purpose of wax infiltration in histology?
Replacing the clearing agent by embedding media, the tissues are infiltrated by a substance which is molten when hot and solid when cold, such as wax.
What is the process of embedding?
Tissues are placed in the moulds and are solidified for cutting.
How can the tissue samples be cut once embedded?
- Botanical microtome
Why do we need to stain tissues?
- Enhances contrast in images from am microscope.
What are examples of basic staining mechanisms?
- Elective solubility
- Metallic impregnation
- Histochemical reactions
- Staining with dyes
What are some common stains in Histopathology?
General structure - Methylene blue
Connective tissue and muscle - van Gieson
Carbohydrates - PAS or alcian blue
Micro-organisms - Gram stain, Ziehl-Neelsen
Lipids - Sudan black
Neurological tissues - luxol fast blue
What type of stains are used in cytopathology?
- Papanicolaou, used for wet-fixed materials
- Romanowsky stains - air-dried specimens
What is Immunohistochemistry?
Antibodies specific to tissue proteins are being used to stain tissue structures. The antibodies can be fluorescently labelled to produce the colour.
What are the The Principles of Immunohistochemistry?
Localise antigens in tissue sections by the use of labeled antibodies in antigen-antibody interactions which are shown by markers such as fluorescent dye or radioactive elements.
What is the direct method of Immunohistochemistry?
The labelled antibody is attached directly to the tissues antigen.
What is the indirect method of Immunohistochemistry?
An antibody attaches to the primary antibody which has the marker on.
What is the most common stain in histology and cytology?
Histology - Haematoxylin and eosin
Cytology - Papanicolau