introduction to histology Flashcards
define histology
the microscopic study of normal cells and tissues
define pathology
the microscopic study of diseased cells and tissues
name the four biomolecules of life
proteins, carbohydrates, lipids and nucleic acids (DNA/RNA)
define tissues
groups of similar cells working together to perform a particular function
define organs
two or more tissues interacting with each other
define system
groups of organs interacting with each other
name the four main tissue types
epithelial, muscle, nervous and connective
describe the function of light microscopes
- reveal basic cellular structure
- 0.2 micrometre resolution
- most commonly used for histology
describe the function of electron microscopes
- reveal ultrastructure
- 1 nanometre resolution
why does microscopy require thin tissues?
to allow light/electrons to pass through
what are the stages of microscopy preparation?
- specimen collection, fixation, dehydration, embedding
what are the different methods of specimen collection?
- incision/punch biopsy
- needle biopsy
- endoscopic biopsy
what is the purpose of fixation?
- preserves the structural arrangement between cells and extracellular components
- stops all biochemical reactions, stopping enzyme activity, preventing tissue decomposition and microbial growth (dead cells release enzymes which degrade the tissue)
what are common fixative examples?
formaldehyde and glutaraldehyde
what is the purpose of dehydration?
- paraffin embedding is NOT compatible with water so it must be removed from the tissue
- this is done using a series of graded alcohols
- the water is removed gradually to prevent the tissue being distorted
describe tissue embedding
- thin tissues are required for microscopy however most tissues are too delicate to be cut and would distort, therefore, the tissues must be supported before they are cut
- resins and (paraffin) wax are used for this
- paraffin wax is NOT compatible with alcohol so here the alcohol is replaced with xylene
describe tissue sectioning
- tissue sections must be thin and flat- ideally a single layer of cells
- tissue sections should be transparent
- sectioning is done on embedded specimens using a microtome
- ideally around 7 micrometers thick sections of tissue
- the tissue sections are mounted onto glass slides
what is the need for tissue staining?
most cells are colourless and transparent so staining makes them visible
what is the problem with staining following the use of wax?
stains are mainly aqueous therefore not compatible with paraffin wax, this means rehydration of the tissue sample is required to remove the wax
what is H & E staining?
- haemotoxylin and eosin staining
- most common staining technique
- haemotoxylin is basic and dyes acid structures blue/ purple
- eosin is acidic and dyes basic structures red/pink
what is PAS staining?
- periodic acid-schif reaction
- stains complex carbohydrates eg mucins magenta
- complex carbs are tightly packed so stain deeply
- muffins produced by goblet cells, brush borders and basement membranes are all PAS positive
what is Masson trichrome staining?
- stains connective tissues
- nuclei and other basophilic structures stain blue/purple
- collagen stains green/blue
- cytoplasm, muscle, rbc and keratin stain red
what is immunonistochemistry?
- uses antibodies to stain specific cellular proteins
- utilises antibody specificity for their antigen, to reveal these components by joining the antibody to a colour indicator
name some other staining techniques
-rectulin- stains rectulin fibres blue/black
- alcian blue- stains cartilage
- van gieson- stains collagen red and cytoplasm yellow
