Histology of the skin

• Preparing histological specimens for light microscopy

  • stabilise cellular structures by chemical fixation
  • cut into thin slices of 3-10 micrometer thick
  • stain e.g. with haemotoxylin (a basic dye, stains basophilic structures e.g. proteins and membranes, red/pink)
• Preparing histological specimens for electron microscopy

  • cut into ultra-thin slices (50 nanometers thick)
  • stain sections with heavy metal salts (lead citrate and uranyl acetate) that bind nucleic acids and proteins
  • visualise in TEM; heavy metal stains block electrons to create contrast
• Microscopy principles light microscopy

  • 2D image
  • resolution 0.2 micrometres
  • cell features can be determined but more visible upon chemical staining
• microscopy principles of electron microscopy

  • most EM images are transmission rather than scanning
  • EM micrographs can be of varying magnification
  • EM micrographs give better resolution (0.2 nm)
  • stain with electron-dense, metal stains
• Interpreting slides

  • morphology
  • function
  • location
• Interpreting slides - magnification

  • condenser objective magnification is given, usually multiply by 10 for eyepiece magnification
  • look for scale bars on EM and in histology books
  • in absence of scale bar use information e.g. rbc, nucleus
• Nucleus

  • position and shape of nucleus tells
  • crypt base - round typical of epithelial cells, also at base due to mucin content (polarity)
  • smooth muscle - elongated spindle shaped (plane); centre of cell
  • immune cells - plasma cell and eosinophil
  • columnar cell e.g. PIN vs normal prostate
• Histological stains

  • H and E
  • trichrome
  • PAS
• H and E

  • most common stain used in histology
  • DNA and RNA are stained by haematoxylin - nuclei, ribosomes
  • protein and membranes are stained by eosin
• Masson triple stain (trichrome)

  • used to stain matrix components
  • mixture of dyes
  • easily recognised by green or blue staining
  • blue or green - mucus, collagen
  • red - cytoplasm, keratin
• Periodic Acid Schiff (PAS)

  • detects sugar groups - complex carbohydrates
  • glycoproteins, mucins
  • stains a red colour
  • basement membrane (or disruption in metastasis), glycocalyx
• IHC

  • immunohistochemistry
  • detects particular proteins
  • uses an antibody linked to an indicator, usually an enzyme that will produce a colour visible by light microscopy
  • e.g. clinical use and potential future use
• Three skin layers:

  • epidermis
  • dermis
  • hypodermis (subcutaneous layer)
• Epidermis is divided into layers

  • stratum corneum
  • stratum lucidum
  • stratum granulosum
  • stratum spinosum
  • stratum basale
• Thin skin may be missing stratum lucidum.