Pigments (((((((((())))))))))

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    There are two broadcategories of pigments,

    endogenous andexogenous

    Pigments

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    Endogenous pigmentsMelanin

    Melanin is the brown-black, non-haemoglobin derived pigment present in the hair, skin, choroidof the eye, meninges and adrenal medulla.Various disorders of melanin pigmentation cause

    generalized and localized hyperpigmentation:i) Generalized hyperpigmentation e.g. in Addison's

    disease, chloasma observed during pregnancy.ii) Focal hyperpigmentation e.g. caf-eu-lait spots,

    melanotic tumours.iii) Generalised Hypopigmentation: albinism is an

    extreme degree of generalised hypopigmentation.iv) Localised hypopigmentation e.g. leucoderma,

    vitiligo.

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    Alkaptonuria

    This is a rare autosomal recessivedisorder in which there is deficiencyof an oxidase enzyme required for

    break down of homogentisic acidwhich then accumulates in thetissues and is excreted in the

    urine(homogentisic aciduria). Thepigment is melanin-like and isdeposited both intracellularly and

    intercellularly in the cartilages,

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    Haemoprotein-derived pigments

    Haemoproteins are the mostimportant endogenous pigmentsderived from haemoglobin,

    cytochromes and their break-downproducts. In disordered ironmetabolism and transport,

    Haemoprotein-derived pigmentsaccumulate in the body. Thesepigments are haemosiderin, acid

    haematin(haemozoin), bilirubin, and

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    parenchymatous deposition of haemosiderin in liver, pancreas,kidney, and heart.Reticuloendothelial deposition in

    the liver, spleen, and bonemarrow. Generalised or systemicoverload of iron may occur due to

    the following causes:i) Increased erythropoietic activityii) Excessive intestinal absorption of

    iron

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    ACIDHAEMATIN(HAEMOZOIN)

    It is a Haemoprotein-derived-brown-blackpigment containing haemiron in ferric form in acidic

    medium. Haematinpigment is seen most

    commonly in chronic

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    BILIRUBINBilirubin is the normal non-ironcontaining pigment present in the bile. Itis derived from porphyrin ring of thehaem moiety of haemoglobin. Excess of

    bilirubin or hyperbilirubinaemia causesan important clinical condition called

    jaundice. Jaundice may appear in one of

    the following 3 ways:a) prehepatic or haemolyticb) Posthepatic or obstructive

    c) hepatocellular

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    PORPHYRINSPorphyrins are normal pigmentpresent in haemoglobin,

    myoglobin and cytochrome.Porphyria refers to anuncommon disorder of inborn

    abnormality of porphyrinmetabolism. Porphyrias are of two broad types:

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    po usc n wear an ear pigment)

    Lipofuscin or lipochrome isyellowish-brown intracellular lipid pigment. The pigment isoften found in atrophied cells of old age and hence name wear and tear pigment. It is seen inthe myocardial fibres,hepatocytes, leydig cells of thetestes and in neurons in senile

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    Microscopic appearance

    The pigment is coarse, golden-brown granular and often

    accumulates in the central partof the cells around the nuclei. Inthe heart muscle, the change is

    associated with wasting of themuscle and is commonlyreferred to as brown atrophy of

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    PIGMENTSEXOGENOUS pigments are the pigments introduced intothe body from outside such as inhalation, ingestion or inoculation.

    INHALED PIGMENTS Anthracosis(deposition of carbon particles) is seen in

    almost every adult lung and generally provokes noreaction of tissue injury

    INGESTED PIGMENTSChronic ingestion of some metals may produce

    pigmentation, e.g. argyria, chronic lead poisoning,melanosis and carotenaemia .

    INJECTED PIGMENTS(TATTOOING)Pigments like India ink, cinnabar and carbon are injected in

    the process of tattooing.