Introduction to histology
Histology is the science of the microscopic structure of cells, tissues, and organs.
Tissues have two interacting components:
1. Cells
2. extra cellular matrix (ECM)
, The ECM supports the cells and contains fluid transport nutrients to the body and carry away
the waste products. Most common procedure used in histologic research is the preparation of
tissue slices or “sections” that can be examined with transmitted light.
Histologic techniques
Fixation
To preserve tissue structure and prevent degradation by enzymes released from the cell or
microorganisms, pieces of organs are placed in solutions of stabilizing or crosslinking
compounds called fixatives. Fixative must fully diffuse to preserve all the cells, and the tissues
are cut into small pieces. Typically introduced via blood vessels with vascular perfusion allowing
fixation rapidly throughout the tissues. Common fixative used for light microscopy is formalin, a
buffer isotonic solution of 37% formaldehyde.
Embedding and sectioning
To permit this sectioning, fixed tissues are infiltrated and embedded in a material that imparts a
firm consistency. Embedding materials include paraffin, used routine for light microscopy and
plastic resin which are adopted for light and electron microscopy. Before infiltration the fixed
tissue is dehydrated by having its water extracted gradually by transfers through a series of
increasing ethanol solutions ending in 100% ethanol. Ethanol is then replaced by an organic
solvent miscible with both alcohol and embedding medium, referred to as cleaning.
Fully cleared tissue is then placed in melted paraffin in an oven at 52°C to 60°C, which
evaporates the clearing solvent and promotes infiltration of the tissues with paraffin and then
embedded by allowing it to harden in a small container of paraffin at room temperature.
Histology is the science of the microscopic structure of cells, tissues, and organs.
Tissues have two interacting components:
1. Cells
2. extra cellular matrix (ECM)
, The ECM supports the cells and contains fluid transport nutrients to the body and carry away
the waste products. Most common procedure used in histologic research is the preparation of
tissue slices or “sections” that can be examined with transmitted light.
Histologic techniques
Fixation
To preserve tissue structure and prevent degradation by enzymes released from the cell or
microorganisms, pieces of organs are placed in solutions of stabilizing or crosslinking
compounds called fixatives. Fixative must fully diffuse to preserve all the cells, and the tissues
are cut into small pieces. Typically introduced via blood vessels with vascular perfusion allowing
fixation rapidly throughout the tissues. Common fixative used for light microscopy is formalin, a
buffer isotonic solution of 37% formaldehyde.
Embedding and sectioning
To permit this sectioning, fixed tissues are infiltrated and embedded in a material that imparts a
firm consistency. Embedding materials include paraffin, used routine for light microscopy and
plastic resin which are adopted for light and electron microscopy. Before infiltration the fixed
tissue is dehydrated by having its water extracted gradually by transfers through a series of
increasing ethanol solutions ending in 100% ethanol. Ethanol is then replaced by an organic
solvent miscible with both alcohol and embedding medium, referred to as cleaning.
Fully cleared tissue is then placed in melted paraffin in an oven at 52°C to 60°C, which
evaporates the clearing solvent and promotes infiltration of the tissues with paraffin and then
embedded by allowing it to harden in a small container of paraffin at room temperature.
