Medic_Summaries (IMS) Topic 7
Cells and Tissues
Histology:
- Study of tissues
- Usually at microscopic (or sub-microscopic) level
Reasons to do histology:
- Diagnosis
- Prognosis
- Treatment
Fixation:
- Why bother?:
- Stop decay:
- Intrinsic: autolytic enzymes
- Extrinsic: microbial, trauma
- Preserve morphology
- Formation of x-links within tissue, either by denaturing proteins or by formation of covalent
bonds within tissue
- Formalin:
- Forms covalent bonds between proteins
- Good tissue penetration
- Not good for cytoplasmic structure/nucleic acids
- Alternatives to formalin:
- Glutaraldehyde:
- For electron microscopy
- Poor tissue penetration
- Ethanol:
- For nucleic acids
- Poor morphology
- Freezing:
- Good for nucleic acids, proteins etc.
- Poor morphology
- Refrigeration required
Cut-up: performed by pathologist
- Describing
- Measuring
- Photographing
- Selecting
Wax impregnation:
- Gives tissue rigidity:
- Enables sectioning
- Protects tissue
- Wax is not water-/formalin-, or alcohol-soluble
- It is soluble in other hydrocarbons (benzene) that are also insoluble in water
- Journey to wax:
- Dehydrate in alcohol
- Replace alcohol with xylene
- Replace xylene with hot wax in mould
1 Adapted from Lectures at the University of Leeds Medical School
, Medic_Summaries (IMS) Topic 7
Haematoxylin/eosin:
- Haematoxylin: basic dye that stains acidic
structures blue/purple (DNA in nuclei)
- Eosin: acidic dye that stains basic structures
pink (proteins in cytoplasm)
- Good for overall morphology
- Account for ca. 95% of staining
Special stains:
- Mucin:
- PAS-D:
- Periodic acid-Schiff (PAS)
- Stains basement membrane, glycogen mucopolysacc-
harides and mucins (neutral and acid)
- Add diastase (D) to digest glycogen
- Alcian blue:
- Acid mucins only
- Clinical application in identifying mucin-producing cells
(adenocarcinoma) and fungi
- Connective tissue:
- Masson’s trichrome:
- Tri = three dyes (haematoxylin, acid fuschin, methyl blue)
- Collagen = blue
- Muscle/cytoplasma/RBC = red
- Nuclei = black
- Clinical application in highlighting fibrosis (scarring)
- Fat: oil red ‘O’
- Miscellaneous: Perl’s Prussian blue, ZN stains, etc.
Immunohistochemistry:
- Used to identify a specific molecule of interest (antigen (Ag)) in a cell
- Antibodies (Ab) to this Ag are generated by exposing an animal to this antigen
- Ab is applied and binds to a tissue section
- Second, labelled anti-animal Ab is applied
- More specific than histochemical stains
Epithelia:
- Layers of cells that cover body surfaces/line body cavities
- Basal lamina: part of basement membrane (NOT the same as epithelia)
- Main features:
- Derived from endoderm/mesoderm/ectoderm
- Line all body surfaces except articular cartilage/tooth enamel/anterior iris
- Cellular
- Sit on layer of connective tissue called basal lamina
- Stuck tightly together (intro-cellular junctions/complexes)
- Polarity (apical/basal)
- Avascular (rely on diffusion)
- Regeneration (rapid turn-over)
2 Adapted from Lectures at the University of Leeds Medical School
Cells and Tissues
Histology:
- Study of tissues
- Usually at microscopic (or sub-microscopic) level
Reasons to do histology:
- Diagnosis
- Prognosis
- Treatment
Fixation:
- Why bother?:
- Stop decay:
- Intrinsic: autolytic enzymes
- Extrinsic: microbial, trauma
- Preserve morphology
- Formation of x-links within tissue, either by denaturing proteins or by formation of covalent
bonds within tissue
- Formalin:
- Forms covalent bonds between proteins
- Good tissue penetration
- Not good for cytoplasmic structure/nucleic acids
- Alternatives to formalin:
- Glutaraldehyde:
- For electron microscopy
- Poor tissue penetration
- Ethanol:
- For nucleic acids
- Poor morphology
- Freezing:
- Good for nucleic acids, proteins etc.
- Poor morphology
- Refrigeration required
Cut-up: performed by pathologist
- Describing
- Measuring
- Photographing
- Selecting
Wax impregnation:
- Gives tissue rigidity:
- Enables sectioning
- Protects tissue
- Wax is not water-/formalin-, or alcohol-soluble
- It is soluble in other hydrocarbons (benzene) that are also insoluble in water
- Journey to wax:
- Dehydrate in alcohol
- Replace alcohol with xylene
- Replace xylene with hot wax in mould
1 Adapted from Lectures at the University of Leeds Medical School
, Medic_Summaries (IMS) Topic 7
Haematoxylin/eosin:
- Haematoxylin: basic dye that stains acidic
structures blue/purple (DNA in nuclei)
- Eosin: acidic dye that stains basic structures
pink (proteins in cytoplasm)
- Good for overall morphology
- Account for ca. 95% of staining
Special stains:
- Mucin:
- PAS-D:
- Periodic acid-Schiff (PAS)
- Stains basement membrane, glycogen mucopolysacc-
harides and mucins (neutral and acid)
- Add diastase (D) to digest glycogen
- Alcian blue:
- Acid mucins only
- Clinical application in identifying mucin-producing cells
(adenocarcinoma) and fungi
- Connective tissue:
- Masson’s trichrome:
- Tri = three dyes (haematoxylin, acid fuschin, methyl blue)
- Collagen = blue
- Muscle/cytoplasma/RBC = red
- Nuclei = black
- Clinical application in highlighting fibrosis (scarring)
- Fat: oil red ‘O’
- Miscellaneous: Perl’s Prussian blue, ZN stains, etc.
Immunohistochemistry:
- Used to identify a specific molecule of interest (antigen (Ag)) in a cell
- Antibodies (Ab) to this Ag are generated by exposing an animal to this antigen
- Ab is applied and binds to a tissue section
- Second, labelled anti-animal Ab is applied
- More specific than histochemical stains
Epithelia:
- Layers of cells that cover body surfaces/line body cavities
- Basal lamina: part of basement membrane (NOT the same as epithelia)
- Main features:
- Derived from endoderm/mesoderm/ectoderm
- Line all body surfaces except articular cartilage/tooth enamel/anterior iris
- Cellular
- Sit on layer of connective tissue called basal lamina
- Stuck tightly together (intro-cellular junctions/complexes)
- Polarity (apical/basal)
- Avascular (rely on diffusion)
- Regeneration (rapid turn-over)
2 Adapted from Lectures at the University of Leeds Medical School
