Histology Lecture 1 Flashcards
What is histology?
Is the study of the microscopic structure of tissues
Is this an immature or mature male cetacean gonadal tissue?
Immature
Is this immature or mature male cetacean gonadal tissue?
Mature
What is the order of analysing a sample from start to finish?
- Specimen acquisition
- Gross examination
- Fixation
- Tissue processing
- Tissue embedding
- Tissue sectioning
- Staining
- Microscopic examination
What is the ideal conditions for sample acquisition?
-Samples should be as fresh as possible and not frozen
What is the tissue to fixative ratio?
1:10
What is fixation?
- Preserves tissue specimens in as life-like state as possible
- Prepares the tissue for histology- cleaning and staining
How does fixation preserve tissue samples?
- Prevents autolysis & putrefaction of the cell
- Prevents loss of cellular constituents
- Prevents shrinking, distortion, swelling of the cells
- Kills microorganisms
How does fixation prepare tissues for histology?
- Hardens the tissue
- Establishes chemical sites for stain reactions
What are two types of chemical fixation?
- Coagulant (non-additive) fixatives
- Non-coagulant (additive) fixatives
What is an example of a coagulant fixative?
Ethanol- it disrupts cytoplasm
What is an example of a non-coagulant fixative?
Formalin
What does a coagulant do?
-Causes cytoplasm to become opaque and congeal into a netlike structure/transport gel
What is a non-additive?
Fixatives that react with the tissue but do not add or combine with the tissue
What is an additive?
Binds either to a proteins’ amino or carboxyl group (cross-link), which changes reactivity with stains
-Strengthens cells structure and insures tissue preservation
What are physical methods of fixation?
- Heat fixation
- Microwave fixation
- Freeze drying and freeze substitution
What is the most commonly used fixative?
10% Neutral Buffer formalin
How does formalin preserve tissue samples
Forms cross links between amino acids of proteins
What factors affect the process of fixation?
- Buffers and pH
- Size of sample and duration of fixation
How long does it take for formalin to fix 4mm thick tissue?
8 hours
What happens if the concentration of fixative is too high?
Will lead to excessive artefacts
What effect does temperature have on fixation?
Higher temperature can increase the speed of fixation
It also increases autolysis
What should done about osmolarity (the concentration of salts and solutes in cells)?
The fixative should match the osmolarity of the specimen
How does an automatic tissue processor dehydrate its samples?
- Removes water and fixative from tissue
- To do this the tissue is passed through increasing concentrations of a dehydrating fluid
- To prevent tissue shrinking its around 30%
