Introduction to Histology Flashcards
histology definition
the microscopic study of normal cells and tissues
What is associated with disruption of normal structure and function?
Disease
Pathology definition
the microscopic study of diseased cells and tissues
What are the levels of structural organisation?
Cells, tissues, organs, body systems
Definition of tissue
a group of similar cells working together to perform a particular function
Definition of an organ
two or more different tissues interacting to perform a function
Definition of organ system
A group of organs with related functions working together to perform a life function
what are the 4 main tissue types?
Connective, epithelial, muscle, nervous
Function of epithelial tissue?
Barrier and lining tissue e.g. outer layer of skin
function of connective tissue?
provides structural and functional support e.g. bone, cartilage, (blood)
Function of muscle tissue?
specialised for contraction e.g. cardiac cells
function of nervous tissue
carries information throughout the body via electrical impulses e.g. nerves
two methods of illuminating tissue samples
beam of light or electrons
Which form of microscopy reveals ultrastructure?
Electron microscopy
Resolutions of LM and EM
LM: 0.2uM
EM: 1nm (200 times greater)
Which microscope is commonly used for routine histopathology?
LM
Describe the stages required to collect and prepare tissues for histological examination
- specimen collection
- fixation
- dehydration
- embedding
- sectioning
- staining
- viewing
3 ways to obtain a specimen
incision or punch biopsy, needle biopsy, endoscoping biopsy
What part of the body would punch biopsy be used for?
Skin/oral surfaces
What part of the body is needle biopsy used for? How is it guided?
organs or lumps below the skin. Imaging techniques (MRI, Xray) are often used to guide the biopsy
What part of the body would an endoscopic biopsy be used for?
Body part with a tract e.g. respiratory, alimentary, urinary tract.
Description of endoscopic biopsy
a flexible tube with a light and camera. cutting tools can be used to collect tissue samples.
What is the purpose of the fixation step in specimen preparation?
Preserves the structural arrangement between cells and extracellular components
How does fixation preserve the specimen and prevent tissue decomposition?
terminates all biochemical reactions
Examples of common fixatives
formaldehyde and glutaraldehyde
Why do you need to dehydrate a specimen when preparing it?
Paraffin is used in the next step (embedding) and is not compatible with water
How is a specimen dehydrated?
Gradually to prevent distortion using a series of graded alcohols. (water leaves sample via osmosis).
Why is embedding required when preparing a specimen?
To support the tissue which allows thin sections to be cut
What substances are commonly used for embedding?
Paraffin wax and resins
During embedding, what substance is the alcohol (from dehydration) replaced with and why?
Alcohol is replaced with xylene because paraffin is not compatible with alcohol.
What equipment is used to section an embedded specimen?
Microtome
How thick should the specimen sections be?
approx 7uM
Why is staining needed?
To make components visible and allow the identification of cell and tissue features
Why must paraffin wax be removed and replaced with water before staining?
Most stains are aqueous and therefore not compatible with paraffin.
How is paraffin wax replaced with before staining?
Reversal of dehydration steps - series of more diluted alcohol
Which is the most commonly used stain?
Haematoxylin and eosin (H&E)
How does H&E stain?
Haematoxylin is basic so stains acidic structures (nucleic acids) blue/purple. Eosin is acidic so stains basic structures (cytoplasmic proteins) pink/red.
What does PAS stand for?
Periodic acid-schiff reaction
What does PAS stain?
Complex carbohydrates are stained magenta e.g. mucins produced by goblet cells, brush borders, basement membranes.
What structure does masson trichrome stain?
Connective tissues
What colour are structures stained with masson trichrome
Nuclei (basophilic) - blue/purple
collagen - green/blue
cytoplasm, RBC, keratin - red
Which stain utilises antibody-antigen specificity?
Immunohistochemistry
How does immunohistochemistry staining work?
It uses antibodies complementary to the antigens of the desired structure. The antibodies are bound to an enzymatic or fluorescent indicator.
What does alcian blue stain?
Mucin and cartilage stained blue
what does van Gieson stain?
Collagen - red
nuclei, erythrocytes and cytoplasm - yellow
what does reticulin stain?
reticulin fibres (component of CT) stained blue/black. Usually combined with H&E
Which staining technique can be used to reveal information about the functional properties of cells?
Immunhistochemistry can be used to identify individual cellular proteins and so conveys functional information about cells.
