Pigments: Melanin,lipofuscin,hemosiderin,hemozion,bilirubin etc

Pigment:

In this blog, I will discuss about various exogenous and endogenous pigments like melanin,function of melanin,  lipofuscin, hemosiderin, hemozoin,bilirubin....etc.

Definition: Pigments are colored substances present in the body, either produced within the body or may have entered from outside.

Pigments are of two types:

• Endogenous
• Exogenous

1) Endogenous pigment:

Endogenous pigments are produced within the body. There are several types of endogenous pigments:

a) Melanin:

Melanin is such an important pigment that it principally determines our skin color. Melanin is produced in a cells called "Melanocyte" that is present in the basal layer of the epidermis. Melanin is normally present in skin, hair, meninges, choroid and adrenal medulla of our body. Melanin is produced from tyrosine by the help of an enzyme called tyrosinase. Melanin is a brown to black, fine,non refractile granule of diameter less than 800nm. This feature helps to differentiate melanin from hemosiderin, which is a larger, refractile,golden-brown pigment produced from the breakdown of hemoglobin. 
Functions of Melanin:
The main function of melanin is to protect us from UV radiations.We know that UV radiation can cause DNA damage.Thereby by reducing exposure to UV light, it actually prevents developement of various cancers.
Disorders of pigmentation are either due to increased production(Hyperpigmentation) or decreased production(Hypopigmentation).

Hyperpigmentation is due to-

• Addison disease.
• Adrenogenital syndrome.
• Cafe-au-lait spot.
• Melanocytic tumors
• Dermatopathic lymphadenitis.

Hypopigmentation is due to-

• Vitiligo
• Albinism
• Leprosy
• Scar
• Radiation dermatitis.

Melanin can be bleached by hydrogen peroxide and stained with the help of Masson Fontana argentaffin stain. But other melanin like pigments like Homogentisic acid or carbon can not be stained with this stain.

b)Lipofuscin:

Lipofuscin is an insoluble pigment. It is also known as Lipochrome or "wear &tear" pigment. It is a polymer of lipids and phospholipids in complex with protein. It is derived from the peroxidation of subcellular membranes. It is a revealing sign of lipid peroxidation and free radicle injury.The word "Lipofuscin" is derived from latin word "fuscus" meaning brown.

Lipofuscin is sometime called as residual bodies,because it is thought to be derived from indestible material in lysosome.Lipofuscin is visualized as  yellowish-brown 

intracytoplasmic pigmet perinuclear in location.This pigment is found in myocardium,leydig cells,hepatocytes etc.

Staining property:

• Acid fast structure.
• Stains positive with oil redO.

c) Hemosiderin:

Figure: Hemosiderin

It is a golden yellow ,refractile, granular pigment.

It appears as blue granule in Prussian blue stain.It can be present localized or genaralized and derives from breakdown of hemoglobin.

Localized hemosiderin occurs due to hemorrhage and the pigment is present in the macrophages,fibroblasts and endothelial cells locally.

Generalized deposits occurs in reticuloendothelial cells of liver,spleen and bonemarrow secondary to hemolytic anaemia,hemosiderosis and repeated blood transfusion.

d) Hemozoin:

Brownish black pigment seen in malaria and do not stain with prussian blue.

e)Bilirubin:

Derives from hemoglobin and can be detected by Gmelin reaction stein's technique.  

2) Exogenous pigment:

a) Ingested pigments(Occurs mostly due to metal ingestion)-

    - Argyria

    - Chronic lead poisoning

    - Melanosis coli

    -Carotenaemia.

b) Inhaled pigments

    - Carbon

    - silica

    - Iron 

    - Asbestos.

Figure: Carbon particle in alveolar macrophage

          

c) Injected pigment 

     - Tattooing

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