Histology lecture Flashcards
(28 cards)
Define histology
The microscopic study of tissue structure and function
How many cells are there in the human body?
10^15
How many cell types are in the human body?
200+
How many main types of tissue are there in the human body?
4
What are the three subsets of histology?
- Tissue structure
- Cellular structure
- Sub-cellular structure
Define tissue structure
How cells and extracellular material combine to form a tissue
Define Cellular structure
Cell shape and how intracellular components are organised to support structure and function
Define sub-cellular structure
The analysis of organelles and inclusions
What are the 4 main tissue types?
- Connective
- Nervous
- Muscle
- Epithelial
Define extracellular matrix
A highly organised region outside of cells comprised of complex structures such as collagen fibrils and basement membranes
What is the role of the extracellular matrix?
- Mechanical support for cells
- Transportation of nutrients to cells
- Carrying away metabolites and secretory products
What is the relationship between cells and extracellular matrices?
- Cells produce extracellular matrix components
- Extracellular matrices interact intensely with cells
What is the order of layers of vein and artery wall tissue from inside to outside?
- Endothelium
- Medial layer
- Adventitia layer
5 steps of specimen preparation
- Fixation
- Dehydration
- Clearing
- Embedding
- Sectioning
Aim of tissue processing
Embed a tissue in a solid medium firmly enough to support the structure so that it can be sectioned yet soft enough so that it can be cut without damaging the knife or tissue
How long does specimen preparation take?
16-48 hours
Aims of fixation
- Prevent autolysis and bacterial attack
- Prevent change in size and shape
- Stop enzyme activity
- Allow clear staining of structures
- Preserve as much as possible
Type of fixatives
- Nothing
- Aldehydes - cross link amine groups in proteins
- Ketones - i.e. acetone
- Alcohol fixative - i.e. methanol for coagulated proteins
- Zinc fixative - amino, carboxyl groups (reversible)
- Heavy metal fixative - i.e. osmium tetroxide
- Freezing
Aim of dehydration
Remove fixative and water from the specimen
What is mostly used for dehydration of specimens?
Alcohols such as ethanol and methanol
How are specimens dehydrated?
By exposing them to graded concentrations of dehydration solutions i.e. from 10-100% with 10% graduations in between
Why are specimens gradually dehydrated?
To minimize tissue distortion from diffusion currents
What does specimen clearing do?
Replaces dehydrating fluid with a fluid that is miscible with the embedding medium and dehydrating fluid.
What does the choice of clearing agent depend on?
- Tissue type
- Processing type
- Processor type
- Processing conditions
- Safety
- Cost and convenience
- Speed of clearance
- Ease of removal
- Tissue damage
