hL1 - the study of histology

• define the term histology:

  • the study of tissues and their structures.
  • histopathology = study of tissues affected by disease.
• define an organ:


  a group of tissues working together to perform a function.
• why study histology?


  Understanding structure and function.

  • structure of each tissue is directly related to its function.
  • understanding cell biology
  • if you understand what is normal, it then helps in identifying, understanding and treating 'abnormal'
  • useful in making diagnosis and severity of a condition.
• what is the resolution of a light microscope?

  1 micro meter - 1mm (0.000001 - 0.001 meters)
• what is the resolution of an electron microscope?

  1 nm - 100 micro meter (0.000000001 - 0.0000001 m)
• why is it necessary to cut thin sections when using a microscope?

  allow light to pass through them and to enable focusing of microscope objectives upon them.
• describe the process of sample preparation from patient:

  • remove specimen from patient (biopsy)
  • accurate labelling as to origin
  • fixation (cross linking of proteins using formaldehyde)
  • dehydration in ascending conc of alcohol, 70%, 95%, 100%
  • clearing with xylene to remove ethanol
  • embedding "strengthening" usually in paraffin was at 600C.
• describe the process of sample preparation when using a microscope:

  • sectioning to produce 5-10 micro meter thick slices.
  • removal of wax by a solvent (xylene)
  • rehydration since most stains are water soluble
  • staining
  • dehydration in ascending alcohols
  • mounting - resin embedding of slide to preserve tissue section.
• sample preparation involving mineralized tissues:

  • tissues from the mouth can be soft or mineralized or both.
  • following fixation, these require demineralization in acids or chelating agents, sometimes for several weeks.
  • then proceed with normal procedure.
• where is haematoxylin commonly used:

  • general staining when paired with eosin
  • stains the nucleus blue
  • stains nucleic acids
• where is eosin commonly used:

  • general staining when paired with haematoxylin
  • stains the cytoplasm pink
  • stains the red blood cells orange/ red
  • stains the collagen fibers pink
  • specifically stains elastic and reticular fibers pink.
• where is toluidine blue commonly used:

  • general staining
  • stains nucleus blue
  • stains cytoplasm blue
  • stains red blood cells blue
  • stains collagen fibers blue
  • high affinity for acidic components, therefore, staining tissues rich in DNA and RNA
• where is masson's trichrome stain commonly used:

  • commonly used with connective tissues
  • stains nucleus black
  • stains cytoplasm red/ pink
  • stains red blood cells red
  • stains collagen fibers blue/ green
  • stains cartilage blue/ green
  • stains muscle fibers red
• where is mallory's trichrome stain commonly used:

  • commonly used with connective tissues
  • stains nucleus red
  • stains cytoplasm pale red
  • stains red blood cells orange
  • stains collagen fibers deep blue
  • specifically stains keratin orange, cartilage blue, bone deep blue, and muscle fibers red.
• where is periodic acid schiff stain commonly used:

  • basement membrane, localizing carbohydrates
  • stains nucleus blue
  • stains collagen fibers pink
  • specifically stains glycogen and other carbohydrates magenta.
• what does the Occular lens do in a light microscope?

  Magnify

  standard magnification is 10x
• what does the Objective lens do in a light microscope?

  Magnify

  specimen visualization

  magnification power of 40x - 100x
• what does the specimen stage do in a light microscope?

  Supports the slide using stage clips
• what do the couse and fine focus knobs do in a light microscope?

  Course focus: Adjusts the stage up and down to bring the specimen into rough focus. Fine focus: Allows for precise focusing by making small adjustments to the focus.
• what does the aperture do in a light microscope?

  hole on the microscope stage through which the transmitted light from the source reaches the stage.

  Controls light intensity.
• what does the condenser do in a light microscope?

  Focuses light form the illuminator into the specimen.

  major role in ensuring clear sharp images are produced.
• describe transmission and scanning electron microscope:

  • high magnification and resolution
  • light source replaced by a beam of electrons
  • specimen has to be specially prepared (gold coated), held inside a vacuum chamber because electrons do not travel very far in air
  • lens replaced by a series of coil shaped electromagnets through which the electron beam travels and focuses them on the image
  • image formed on the monitor.
• what are the limitation of microscope methods:

  • light microscopes have a relatively low resolution
  • both TEM and SEM have a much higher resolution
  • magnification too high for most needs
  • very expensive
  • specimen preparation difficult
  • can only look at tiny specimens
  • light and TEM microscopes give a 2D view, this can limit our understanding of a 3D object or process
  • SEM views provide a pseudo 3D image, but do not necessarily provide understanding.