Chapter 1: Histology and methods of study
ECM: consists of many macromolecules forming complex structures (collagen fibrils and
basement membrane)
Steps to prepare tissue:
o Fixation: placed in solution that inhibits degradative enzymes and preserves it.
o Dehydration: transferred to alcohol to remove water
o Clearing: alcohol is removed
o Infiltration: place tissue in melted paraffin ( toluene or xylene at 52-60 degrees)
o Embedding: place tissue in small mold and allowed to harden.
o Trimming: trim paraffin block to expose tissue on a microtome ( 1-10 um)
Microtome: used for sectioning paraffin-embedded tissue for light microscopy.
Fixatives: compounds that cross-link and stabilize (used in fixation)
o Formalin is a commonly used fixative 37% formaldehyde.
Formaldehyde and glutoraldehyde react with the amine groups (NH3) of tissue proteins
prevents their degradation.
Osmium tetroxide: preserves and stains membrane lipids and proteins.
Embedding material: gives the tissue rigid consistency.
o Paraffin: Used for light microscopy
o Plastic Resins: for light and electron microscopy
1 Angstrom = 0.1 nm / 1 Angstrom = 100 picometers
Milli, micro, nano, pico (-3, -6, -9, -12)
Staining:
o If anionic (net-ve charge) : stained by basic dyes basophilic
Nucleic acids, DNA, RNA, glycosaminoglycans
o If cationic (net +ve charge) : stained by acid dyes acidophilic
Proteins, mitochondria, secretory granules, collagen…
ECM: consists of many macromolecules forming complex structures (collagen fibrils and
basement membrane)
Steps to prepare tissue:
o Fixation: placed in solution that inhibits degradative enzymes and preserves it.
o Dehydration: transferred to alcohol to remove water
o Clearing: alcohol is removed
o Infiltration: place tissue in melted paraffin ( toluene or xylene at 52-60 degrees)
o Embedding: place tissue in small mold and allowed to harden.
o Trimming: trim paraffin block to expose tissue on a microtome ( 1-10 um)
Microtome: used for sectioning paraffin-embedded tissue for light microscopy.
Fixatives: compounds that cross-link and stabilize (used in fixation)
o Formalin is a commonly used fixative 37% formaldehyde.
Formaldehyde and glutoraldehyde react with the amine groups (NH3) of tissue proteins
prevents their degradation.
Osmium tetroxide: preserves and stains membrane lipids and proteins.
Embedding material: gives the tissue rigid consistency.
o Paraffin: Used for light microscopy
o Plastic Resins: for light and electron microscopy
1 Angstrom = 0.1 nm / 1 Angstrom = 100 picometers
Milli, micro, nano, pico (-3, -6, -9, -12)
Staining:
o If anionic (net-ve charge) : stained by basic dyes basophilic
Nucleic acids, DNA, RNA, glycosaminoglycans
o If cationic (net +ve charge) : stained by acid dyes acidophilic
Proteins, mitochondria, secretory granules, collagen…
