L2- Examining Cells and Tissue Flashcards
standard measurement of cell size
um
what is used for sizing of cells under microscope
graticule
enlarged red bloods cells
indication for some forms of vasculitis
resolution definition
The smallest distance by which two objects can be separated and still be distinguishable as two separate objects.
the higher the resolving power
the more easily two objects can be distinguished
lens of eye has
low resolution
resolving power increase with
increasing magnifying class
smallest human cell seen by naked eye
Oocyte
name 2 main types of microscopy
light and electron
smallest organelle seen with light microscopy
mitochondria
smallest organelle seen with electron microscopy
ribosome
light microscopy uses
a visible light source and glass lenses to look at specimens up to 1500X magnification and 0.2um resolving power
electron microscopy uses
a beam of charged electrons and electromagnetic lenses to look at specimens at up to 500,000X magnification and 0.5nm resolution.
when is electron microscopy used
technique for obtaining high resolution of biological specimens. Used to investigate detailed structure of tissues, cells, organelles and macromolecular complexes.
- High resolution= due to use of electrons
why does electron microscopy give higher resolution
uses lectern beam- shorter wavelength than light
advantages of light microscpy
- can view images in natural colours
- large field of view
- cheap and easy prep
- can view living and moving objects
disadvantages of light microscope
lower magnification (x600) Lower resolution 0.25um
advantages of electron microscopy
- higher magnification (x500,000)
- higher resolution (0.25nm)
disadvantages of electron microscopy
- can only view dead objects
- difficult and epxsneiv to prep
- limited field of view
- only monochrome images can be seen
types of light microscopy
1) Phase contrast
2) Dark field
3) Confocal microscopy
phase contrast
combines interference of 2 light waves
- enhances images of use unstained cells
dark field
- Very specialised technique used with living cells
- Illuminates the sample with light that will not be collected by the objective lens and thus will not form part of the image
- This produces the classic appearance of a dark, almost black background with bright objects on it
- Can be used in EM images
confocal microscopy
captures multiple 2D images at different depths to reconstruct 3D structures
- use with Immunofluorescence
type sof elektron microscopy
Tranmission
Scanning
TEM
o Used to view thin specimens through which electrons can pass through (same principles as a light microscope)
o 2 dimensional
o Used to image the interior of cells, structure of protein molecules and organisation of molecules in viruses and cytoskeletal filaments etc.
o Small amount of sample can be analysed at a time
SEM
o Depends on the emission of secondary electrons from the surface of a specimen
–> sample can be thick
o Provides detailed images of the surfaces of cells and whole organisms not possible by TEM
o 3-dimensional
o Large amount of sample can be analysed at a time
o Images can be colourised
how many micrometers (um) in a millimetre
1000
how many micrometers in a nanometer (nm)
1000
histology is important in order to
visualise content and architecture of the cells
to distinguish between certain pathologies e..g benign or maligant
Sample preparation steps
1) Tissue procurement
2) Tissue fixation
3) Embedding
4) Staining
procurement means
biopsy- removal of a small piece of tissue from an organ or tissue for microscopic examination
examples of tissue procurement methods
- Curettage (endometrium)
- Transvascular
- Needle aspiration
Curettage
scraping method for uterine tissue
Needle aspiration
bone marrow, synovial fluid, thyroid tissue
transvascular
venepuncture e.g. ABG analyst
two ways of tissue fixing
1) Paraffin- embedded tissue section
2) Frozen section
Paraffin- embedded tissue section
also involves embedding
- formalin used to kill sample and prevent putrefaction
- melted paraffin wax- to embed tissue for slicing
- microtome- slice tissue into v thin slice
- staining: H&E
Frozen section
- surgical specimens frozen to -20 and -30
- cryostat- slice tissue
- staining: H&E
paraffin wax formalin and frozen section are methods which
samples stay true to their original form
- preservation of biological tissue from decay due to autolysis and putrefaction
paraffin wax formalin fixed sample stay true to their original form due to
cross bridges formign the sample
paraffin wax embedding method (after fixation)
- Dehydrated in different concentrations of alcohols
- Immersed in dissolved paraffin wax (hot) overnight
- Tissue orientated in a mould and more wax added
- Allowed to cool to room temperature
- Gently eased out of mould
both paraffin embedded and frozen section samples can be stained with
Haematoxylin and Eosin
Haematoxylin and Eosin
principle tissue stain in medical diagnosis
haemtoxylin stains
nucleic acid- (acid- negative) blue
Eosin stains
proteins in the cytoplasm and extracellular - pink
name two other routine staining methods
massons trichome
periodic acid-schiff stain
In massons trichome what colour does keratin and muscle fibre go
red
In massons trichome what colour does collagen dn bone go
blue or green
In massons trichome what colour does cytoplasm go
red or pink
In massons trichome what colour does nuclei go
dark brown to black
period acid-schiff stains
anything with a sugar attached
embedding the tissue
allows the sample to be sliced very thinly e.g. melted paraffin wxx sets hard when cooled
what is used to fix/ preserve a sample
formalin
why do we stain a tissue
to see cell components
what is quicker to do paraffin-embedded tissue section or frozen section
paraffin-embedded tissue section: 24-48h
frozen section: 10 -20 mins
morphology of paraffin-embedded tissue section and frozen section under a microscope
paraffin-embedded tissue section- clarity
frozen section- opaque
application of paraffin-embedded tissue section
pathological diagnosis
application of frozen section
intraoperative
how long can a paraffin-embedded tissue section be kept
permanant
how long can a frozen section be kept
months
RBC and H&E
pink and white int he middle- no DNA or protein where the nuclei is meant to be
fat and H&E
cannot be visualised
preparation of live cells
- ‘cutting and ‘dicing’ o collagenase and DNAse centrifugation steps on basis of cell density o Put cells in appropriate growth medium o Culture enzymes View under phase contrast microscope
what needs to be maintained constant in the internal environment when preparing live cells
Conc of oxygen, CO2, salt and other electrolytes
Conc of nutrients and waste products
pH
Temp
Volume and pressure of fluid and cell compartments equalised
cells in culture allow
experiments to determine cells and thus tissue function e.g. endothelial cells induced to die through programmed cell death
advantage of cell culture
- Absolute control over the physical environment
- Homogeneity of sample
- Less need for animal models
disadvantage of cell culture
- Hard to maintain
- Only grow small amount of tissue at high cost
- Dedifferentiation
- Instability, aneuploidy
- 3 dimension architecture lost
- influence of other cells/ tissue not maintained.
immunohistochemsitry
antibody labelled with enzyme
immunofluorescence
antibody labelled with fluorescent markers
- antibody bind to antigen
- fluorophore emits visible light