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1. HISTOLOGICAL PIGMENTS DENNIS MBURU- BMLS/039/2014 FRIDAH MURAGE- BMLS/008J/2013 STEPHEN KITHEKA- BMLS/025J/2014 ODEK VANESSA AWUOR- BMLS/031J/2014 KIPNG’ETICH IAN - BMLS/013J/2014

2. Histological pigments are pigments found in tissues extracted from the body other than the ones from stains and fixatives There are three types of histological pigments: Artifact pigments Endogenous pigments Exogenous pigments

3. Artifact pigments Occur as a result of fixation e.g. through improper fixation, poor dehydration. They lie on top of tissues not within cells Examples are; formalin, mercury, chrome and picrate

4. Formalin Occur as a result of fixation in acid formalin Associated with blood containing tissues Appears brown in tissues but at times might appear as a fine black precipitate due to formation of a formalin- heme pigment It is resistant to strong acids thus can be removed by using alcoholic picric acid

5. Mercury Occurs in mercury containing fixatives e.g. Zenker’s Appears reddish in tissues Can be removed by iodine followed with hypo sodium thiosulphate

6. Chrome As a result of fixatives containing potassium dichromate e.g. Zenker’s Removed by washing thoroughly in water prior to dehydration.

7. Picrate Occurs in fixatives containing picric acid e.g. Bouin’s Removed by saturated aqueous lithium carbonate

8. Endogenous pigments They are formed within the body Can be broadly categorized into 2: Hematogenous - contain heme , hemoglobin derived e.g. hemosiderin Non- hematogenous - lack heme e.g. melanin , lipofuschin

9. Hemosiderin Is a granular crystalline pigment golden yellow to brown in color Caused by; Increased absorption of iron in the diet Impaired iron utilization Excess hemolysis Iron overload during blood transfusion

10. Lipofuschin Originates from lysosomal breakdown of products of lipids Found in aged/ chronically injured tissues In tissue sections it appears as a yellow- brown, finely granular and peri -nuclear,

11. Melanin Brown – black pigment found in tissue sections from the skin

12. Exogenous pigments These are those taken into the body externally they include; carbon, tattoo ad asbestos

13. carbon Inhaled through pollution Appears black in tissues It resists bleaching and insoluble in acid

14. Tattoo Found in skin and lymph nodes it’s a localized pigment

15. asbestos Its found coated with iron in tissues of the lungs. It stains positive with Pearl’s