CELLS AND TISSUES
INTRODUCTION TO HISTOLOGY
Histology: study of tissues usually at the microscopic/sub-microscopic level
Fixation
• Stop decay
o Intrinsic – autolytic enzymes
o Extrinsic – microbial, trauma
• Preserve morphology
• Formation of x-links within tissue, either by denaturing proteins or by the formation of covalent bonds within the
tissue
Formalin
• Forms covalent bonds between proteins
• Good tissue penetration
• Not good for cytoplasmic structure or nucleic acids
Alternatives of formalin
• Glutaraldehyde
o For electron microscopy
o Poor tissue penetration
• Ethanol
o For nucleic acids
o Poor for morphology
• Freezing
o Good for nucleic acids, proteins etc.
o Poor for morphology
o Refrigeration required
Wax impregnation
• Gives tissue rigidity
o Enables sectioning
o Protects tissue
• Wax is not water/formalin, or alcohol soluble
• It is soluble in other hydrocarbons e.g. benzene (which are also insoluble in water)
Staining
• Highlight structure of interest in a cell
• Haematoxylin: stains acidic structures blue or purple, e.g. DNA in nuclei
• Eosin: acidic dye that stains basic structures pink, e.g. proteins (cytoplasm)
• Haematoxylin and eosin account for 95% of staining
Special stains
• Mucin: Alcian Blue, PAS (stains basement membrane, glycogen, mucopolysaccharieds and mucins); diastase digests
glycogen
• Connective tissue: Masson’s trichrome (haematoxylin, acid fuschin, methyl blue)
o Collagen = blue
o Muscle/cytoplasm/RBC = red
o Nuclei = black
• Fat: Oil red ‘O’
• Misc: Perl’s Prussian Blue, ZN stain, others
Immunohistochemistry
• Used to identify a specific molecule of interest (antigen (Ag)) in a cell
• The antibodies (Ab) to this Ag are generated by exposing an animal e.g. rabbit, to this antigen
• This Ab is applied and binds to a tissue section
• A second, labelled anti-rabbit Ab is applied
, RAS-RAF pathway
RAS-GTP (activated RAS) → BRAF → MEK → ERK →normal cell proliferation and survival
EPITHELIA
Epithelium – layer of cells that cover the body surfaces (internal, external) or line body cavities
Main features
• Derived from germ cell layers – endoderm, mesoderm, ectoderm (nervous system derived from)
• Line all body surfaces apart from articular cartilage, tooth enamel, anterior iris
• Sit on a layer of connective tissue – basal lamina (part of the basal membrance)
• Stuck closely together – intra-cellular junctions/complexes
• Polarity – apical/basal i.e. top/bottom
• Avascular –no direct blood supply, rely on diffusion
• Regeneration – rapid-turn-over
Main functions
1. Absorption (e.g. stomach / small / large intestine)
2. Surface movement (e.g. cilia in airways / fallopian tube)
3. Secretion of substances (e.g. glands such as sweat, pancreas)
4. Gas exchange (e.g. lungs)
5. Surface lubrication (e.g. mesothelial linings – pleural / pericardial / peritoneal)
6. Sensation
7. Protection
Cell-cell adhesion complexes
• Without them, cell would fall apart
• TJs: occludin/claudin seals to protein movement/paracellular diffusion; apical
• AJs: transmembrane proteins connect across cell cytoskeletons, below TJs
• GJs: small channels, allow intercellular ion/small molecule exchange
• DSs: Transmembrane proteins connect to others (linked to intermediate
filaments) form adjacent cells
• HDs: provide attachment to underlying basal lamina
• CAMs are critical for epithelium integrity, adherence to underlying basal lamina and intrinsic function
Naming/classification of epithelia
• Number of cells, shape, specialisations
• 1 layer – simple
o Squamous
o Cuboidal
o Columnar
o Pseudo-stratified – columnar cells of different heights, looks like multiple layers; upper airways,
cilia/goblet cells
• Multi-layered – stratified
o Squamous – skin, oesophagus, oral cavity
o Cuboidal
o Columnar
o Transitional – changes shape (columnar and flat),
distention; bladder/urinary tract
Specialisation
• Cilia
• Secretory – mucus for protection and lubrication
• Microvilli – increase SA for absorption
• Keratinisation – forms a protective layer
Epithelium for protection
• Prevents dehydration, chemical, mechanical etc. damage
• Covering of inter/outer surfaces
• Multi-layered for strength – i.e. stratified
• Replicative to replace sloughed / damaged cells
• Tight seals between cells
INTRODUCTION TO HISTOLOGY
Histology: study of tissues usually at the microscopic/sub-microscopic level
Fixation
• Stop decay
o Intrinsic – autolytic enzymes
o Extrinsic – microbial, trauma
• Preserve morphology
• Formation of x-links within tissue, either by denaturing proteins or by the formation of covalent bonds within the
tissue
Formalin
• Forms covalent bonds between proteins
• Good tissue penetration
• Not good for cytoplasmic structure or nucleic acids
Alternatives of formalin
• Glutaraldehyde
o For electron microscopy
o Poor tissue penetration
• Ethanol
o For nucleic acids
o Poor for morphology
• Freezing
o Good for nucleic acids, proteins etc.
o Poor for morphology
o Refrigeration required
Wax impregnation
• Gives tissue rigidity
o Enables sectioning
o Protects tissue
• Wax is not water/formalin, or alcohol soluble
• It is soluble in other hydrocarbons e.g. benzene (which are also insoluble in water)
Staining
• Highlight structure of interest in a cell
• Haematoxylin: stains acidic structures blue or purple, e.g. DNA in nuclei
• Eosin: acidic dye that stains basic structures pink, e.g. proteins (cytoplasm)
• Haematoxylin and eosin account for 95% of staining
Special stains
• Mucin: Alcian Blue, PAS (stains basement membrane, glycogen, mucopolysaccharieds and mucins); diastase digests
glycogen
• Connective tissue: Masson’s trichrome (haematoxylin, acid fuschin, methyl blue)
o Collagen = blue
o Muscle/cytoplasm/RBC = red
o Nuclei = black
• Fat: Oil red ‘O’
• Misc: Perl’s Prussian Blue, ZN stain, others
Immunohistochemistry
• Used to identify a specific molecule of interest (antigen (Ag)) in a cell
• The antibodies (Ab) to this Ag are generated by exposing an animal e.g. rabbit, to this antigen
• This Ab is applied and binds to a tissue section
• A second, labelled anti-rabbit Ab is applied
, RAS-RAF pathway
RAS-GTP (activated RAS) → BRAF → MEK → ERK →normal cell proliferation and survival
EPITHELIA
Epithelium – layer of cells that cover the body surfaces (internal, external) or line body cavities
Main features
• Derived from germ cell layers – endoderm, mesoderm, ectoderm (nervous system derived from)
• Line all body surfaces apart from articular cartilage, tooth enamel, anterior iris
• Sit on a layer of connective tissue – basal lamina (part of the basal membrance)
• Stuck closely together – intra-cellular junctions/complexes
• Polarity – apical/basal i.e. top/bottom
• Avascular –no direct blood supply, rely on diffusion
• Regeneration – rapid-turn-over
Main functions
1. Absorption (e.g. stomach / small / large intestine)
2. Surface movement (e.g. cilia in airways / fallopian tube)
3. Secretion of substances (e.g. glands such as sweat, pancreas)
4. Gas exchange (e.g. lungs)
5. Surface lubrication (e.g. mesothelial linings – pleural / pericardial / peritoneal)
6. Sensation
7. Protection
Cell-cell adhesion complexes
• Without them, cell would fall apart
• TJs: occludin/claudin seals to protein movement/paracellular diffusion; apical
• AJs: transmembrane proteins connect across cell cytoskeletons, below TJs
• GJs: small channels, allow intercellular ion/small molecule exchange
• DSs: Transmembrane proteins connect to others (linked to intermediate
filaments) form adjacent cells
• HDs: provide attachment to underlying basal lamina
• CAMs are critical for epithelium integrity, adherence to underlying basal lamina and intrinsic function
Naming/classification of epithelia
• Number of cells, shape, specialisations
• 1 layer – simple
o Squamous
o Cuboidal
o Columnar
o Pseudo-stratified – columnar cells of different heights, looks like multiple layers; upper airways,
cilia/goblet cells
• Multi-layered – stratified
o Squamous – skin, oesophagus, oral cavity
o Cuboidal
o Columnar
o Transitional – changes shape (columnar and flat),
distention; bladder/urinary tract
Specialisation
• Cilia
• Secretory – mucus for protection and lubrication
• Microvilli – increase SA for absorption
• Keratinisation – forms a protective layer
Epithelium for protection
• Prevents dehydration, chemical, mechanical etc. damage
• Covering of inter/outer surfaces
• Multi-layered for strength – i.e. stratified
• Replicative to replace sloughed / damaged cells
• Tight seals between cells
