Pigments and Lipids Flashcards
What are pigments?
- self coloured materials, can be seen in unstained solution
- limited range of colour; yellow-brown or brown-black
Artefact pigments
- deposit produced as a result of chemical reaction in tissue
- not originally part of tissue
Exogenous pigments
- present in original tissue
- some pathological, some indicative of person’s lifestyle/employment
- gain accidental access through industrial exposure; inhalation or implantation
Endogenous pigments
- produced within tissue and have physiological function
- or by-product of normal metabolic process
Schmorl’s test
- yellow pigment turning green = positive result
- may be difficult to see if reaction has occurred
Types of artefact pigments (5)
- Formalin
- Malarial
- Mercury
- Osmium
- Dichromate deposits
Types of endogenous pigments (8)
- Bile pigments
- Lipofuscin
- Melanin
- Iron
- Copper
- Uric Acid and Urates
- Calcium
- Haemoglobin
Types of exogenous pigments (3)
- Carbon
- Asbestos
- Silica
Formalin pigment
- brown/black deposit following acid formalin fixation
- most easily seen around old/degenerated blood in tissues
- removed w/ picric acid
Malarial pigment
- similar to formalin; formed in/near RBCs
- also found in cytoplasm of macrophages that have ingested affected RBCs
- parasite presence within RBCs helps identify pigment source
Mercury pigment
- black deposit formed w/ mercury-containing fixatives
- removed w/ iodine and sodium thiosulphate
- less common in modern histology
Osmium pigment
- very dense black pigment following osmium tetroxide fixation
- removed by oxidation w/ hydrogen peroxide
Dichromate deposits
- occurs when chrome salts reacts w/ alcohols and produces brown oxide
- potassium dichromate fixation form yellow/brown deposits
Bile pigments
- breakdown of bile pigments; range of colours in a healing bruise
- difficult to identify; oxidation alters colour
- only large deposits can appear in wax sections
Iron pigment
- stored as haemosiderin in ferric state
- fine brown colour; liver, spleen and marrow
- Perl’s Prussian Blue; detects iron in haemosiderin by potassium ferrocyanide - dense blue precipitate
Melanin pigment
- identified by reducing ability w/ Schmorl’s test
- black/brown pigment; product of melanocytes
- eye, skin, hair, brain and melanoma
Lipofuscin pigment
- ‘wear and tear’ pigment due to lipid oxidation
- most easily identified pigment
- brown or lipochrome pigment
Copper pigment
- normally undetectable
- accumulation (Wilson’s disease)
- important in metabolism (oxidase enzymes)
Calcium pigment
- absorbed in GIT from food (vitamin D)
- demonstrated by Von Kossa (silver impregnation, non specific to calcium - black)
Haemoglobin pigment
- brownish colour in formalin fixed sections
- Eosin in H&E gives orange/pink colour
- free Hb is anamorphous or globular; strongly acidophilic
Uric Acid and Urates pigment
- urate crystals are birefringent
- high uric acids (kidney diseases, overweight, diabetes)
- breakdown of purine nucleotides
- gout; crystallisation in joints
Carbon pigment
- dense, black pigment
- most common of pigments; absorbed by phagocytes
- acts as carrier for more dangerous materials; absorb chemicals onto their surface
- seen in lungs of urban dwellers, smokers; skin from tattoos and needle tracks
Asbestos pigments
- brown pigments
- cause fibrosis, may lead to asbestosis and mesothelioma
- long beaded fibres
Silica pigments
- black-brown, depending on source of it
- may be birefringent
- miners, quarry workers, stonemasons exposed to it
Types of conjugated lipids (7)
- neutral fats
- waxes
- cholesterol esters
- phosphoglycerides
- sphingomyelins
- ceramides
- glycolipids
Types of unconjugated lipids (2)
- fatty acids
- steroids
What are fats and lipids defined by?
- solubility in fat solvents
- insolubility in water
Why is fixation of lipids difficult?
- all but 2 fixatives can be used (osmium tetroxide, potassium dichromate)
- osmium tetroxide fixes lipids but also blackens them
What does lush chrome staining rely on?
- using a dye that’s very soluble in lipids but relatively insoluble in aqueous solvent
What techniques are used with lysochrome methods?
- Sudan dyes
- Oil Red O
- Nile blue
Limitations of techniques with lab methods with lipids?
- melting point 37oC; fluid in body, solid in section, may not stain/react with reagents
- physical properties; pure lipids stain differently from mixtures
What is applied after biopsy of lipids?
- Sudan black B
- Oil Red O
- Polarised light (birefringence)
Haemosiderin
- found in spleen and liver
- iron binding proteins (Fe3+)
- destruction of old RBCs
Diseases associated with haemosiderin
- haemochromatosis
- haemosiderosis
Haemochromatosis
- autosomal recessive disorder
- excessive absorption of iron
- multi-organ disorder
- liver (cirrhosis), heart (myopathy), pancreas (diabetes mellitus)
Haemosiderosis
- focal deposits
- no genetic cause
- alcoholism or thalassaemia (blood transfusions)
- aka secondary haemochromatosis
Solubility in lipid identification
- section cut fixed, frozen tissue
- subsequent short formalin fixation, neutral lipids preserved not fixed
- traditional wax sectioning removes lipids. H&E gives -ve artefact image
- no dehydration/clearing and sections mounted in aqueous mountants
Lipid storage disorders (lipidosis)
- metabolic inherited disorders (rare)
- lipid accumulation in cells (overproduction, decreased metabolism)
- varies in organs; particular in CNS
Fabry disease
- accumulation of lipids in kidney
Osmium tetroxide fixation
- uncommon in light microscopy, blackening lipids
Microscopic examination in lipid identification
- bright-field microscopy (H&E, Sudan-type stains, Oil Red O)
- polarised light microscopy (oval fat bodies in urinary sediment examination - lipiduria
