Pigments and Lipids Flashcards

1
Q

What are pigments?

A
  • self coloured materials, can be seen in unstained solution

- limited range of colour; yellow-brown or brown-black

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2
Q

Artefact pigments

A
  • deposit produced as a result of chemical reaction in tissue
  • not originally part of tissue
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3
Q

Exogenous pigments

A
  • present in original tissue
  • some pathological, some indicative of person’s lifestyle/employment
  • gain accidental access through industrial exposure; inhalation or implantation
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4
Q

Endogenous pigments

A
  • produced within tissue and have physiological function

- or by-product of normal metabolic process

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5
Q

Schmorl’s test

A
  • yellow pigment turning green = positive result

- may be difficult to see if reaction has occurred

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6
Q

Types of artefact pigments (5)

A
  • Formalin
  • Malarial
  • Mercury
  • Osmium
  • Dichromate deposits
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7
Q

Types of endogenous pigments (8)

A
  • Bile pigments
  • Lipofuscin
  • Melanin
  • Iron
  • Copper
  • Uric Acid and Urates
  • Calcium
  • Haemoglobin
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8
Q

Types of exogenous pigments (3)

A
  • Carbon
  • Asbestos
  • Silica
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9
Q

Formalin pigment

A
  • brown/black deposit following acid formalin fixation
  • most easily seen around old/degenerated blood in tissues
  • removed w/ picric acid
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10
Q

Malarial pigment

A
  • 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
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11
Q

Mercury pigment

A
  • black deposit formed w/ mercury-containing fixatives
  • removed w/ iodine and sodium thiosulphate
  • less common in modern histology
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12
Q

Osmium pigment

A
  • very dense black pigment following osmium tetroxide fixation
  • removed by oxidation w/ hydrogen peroxide
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13
Q

Dichromate deposits

A
  • occurs when chrome salts reacts w/ alcohols and produces brown oxide
  • potassium dichromate fixation form yellow/brown deposits
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14
Q

Bile pigments

A
  • 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
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15
Q

Iron pigment

A
  • 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
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16
Q

Melanin pigment

A
  • identified by reducing ability w/ Schmorl’s test
  • black/brown pigment; product of melanocytes
  • eye, skin, hair, brain and melanoma
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17
Q

Lipofuscin pigment

A
  • ‘wear and tear’ pigment due to lipid oxidation
  • most easily identified pigment
  • brown or lipochrome pigment
18
Q

Copper pigment

A
  • normally undetectable
  • accumulation (Wilson’s disease)
  • important in metabolism (oxidase enzymes)
19
Q

Calcium pigment

A
  • absorbed in GIT from food (vitamin D)

- demonstrated by Von Kossa (silver impregnation, non specific to calcium - black)

20
Q

Haemoglobin pigment

A
  • brownish colour in formalin fixed sections
  • Eosin in H&E gives orange/pink colour
  • free Hb is anamorphous or globular; strongly acidophilic
21
Q

Uric Acid and Urates pigment

A
  • urate crystals are birefringent
  • high uric acids (kidney diseases, overweight, diabetes)
  • breakdown of purine nucleotides
  • gout; crystallisation in joints
22
Q

Carbon pigment

A
  • 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
23
Q

Asbestos pigments

A
  • brown pigments
  • cause fibrosis, may lead to asbestosis and mesothelioma
  • long beaded fibres
24
Q

Silica pigments

A
  • black-brown, depending on source of it
  • may be birefringent
  • miners, quarry workers, stonemasons exposed to it
25
Types of conjugated lipids (7)
- neutral fats - waxes - cholesterol esters - phosphoglycerides - sphingomyelins - ceramides - glycolipids
26
Types of unconjugated lipids (2)
- fatty acids | - steroids
27
What are fats and lipids defined by?
- solubility in fat solvents | - insolubility in water
28
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
29
What does lush chrome staining rely on?
- using a dye that’s very soluble in lipids but relatively insoluble in aqueous solvent
30
What techniques are used with lysochrome methods?
- Sudan dyes - Oil Red O - Nile blue
31
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
32
What is applied after biopsy of lipids?
- Sudan black B - Oil Red O - Polarised light (birefringence)
33
Haemosiderin
- found in spleen and liver - iron binding proteins (Fe3+) - destruction of old RBCs
34
Diseases associated with haemosiderin
- haemochromatosis | - haemosiderosis
35
Haemochromatosis
- autosomal recessive disorder - excessive absorption of iron - multi-organ disorder - liver (cirrhosis), heart (myopathy), pancreas (diabetes mellitus)
36
Haemosiderosis
- focal deposits - no genetic cause - alcoholism or thalassaemia (blood transfusions) - aka secondary haemochromatosis
37
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
38
Lipid storage disorders (lipidosis)
- metabolic inherited disorders (rare) - lipid accumulation in cells (overproduction, decreased metabolism) - varies in organs; particular in CNS
39
Fabry disease
- accumulation of lipids in kidney
40
Osmium tetroxide fixation
- uncommon in light microscopy, blackening lipids
41
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