Pathology of Hematogenous pigments

Hematogenous pigments

Hematogenous pigments are the pigments that are derived from hemoglobin of red blood cells (RBCs).

Hemoglobin

It is the normal pigment of erythrocytes. It consists of -

•      a pigment, heme and ,

•      a protein, globin.

Heme consists of a ferrous iron and a porphyrin. Porphyrin consists of four pyrrole rings.

In normal hemoglobin, iron is in ferrous state.

Oxyhemoglobin

When hemoglobin is loosely oxygenated, it is known as oxyhemoglobin (oxidized hemoglobin). The bright red color of arterial blood is due to the presence of oxyhemoglobin.

Methemoglobin

When hemoglobin is fully oxygenated, it is known as methemoglobin/ferrihemoglobin (oxidized hemoglobin).  

It is a true oxide of hemoglobin and is reddish brown/ chocolate brown in contrast to the bright red oxyhemoglobin. It is caused in nitrite, in chlorate and  in some organic compounds poisonings.

Deoxyhemoglobin

When oxyhemoglobin is deoxygenated, it is known as deoxyhemoglobin (reduced hemoglobin). The dark red color of venous blood is due to the presence of deoxyhemoglobin.

Sulfhemoglobin

Sulfhemoglobin is a combination of reduced hemoglobin and inorganic sulfide. It is dark brown in color.

Sulfurmethemoglobin

Sulfur methemoglobin is a combination of methemoglobin and inorganic sulfide. It occurs after death and cause greenish discoloration to abdominal structures.

Carboxyhemoglobin

Sulfur methemoglobin is a combination of hemoglobin and carbon monoxide. When erythrocytes undergo hemolysis, the carboxyhemoglobin carries its dark color to the surrounding fluids and tissues after death that represents postmortem imbibition.

Hematins

Hematins/ acid hematins are pigments formed by the action of acids on hemoglobin. It appears in tissue sections as dark brown finely granular pigment. Hydrochloric acid hematin is often seen within and adjacent to gastric ulcers. It apparently forms from the action of gastric acid with hemoglobin.

In malaria, hematins are present in erythrocytes and in the cytoplasm of reticuloendothelial cells in spleen, lymph nodes, liver and bone marrow.

Hemosiderin

Hemosiderin is a shiny, golden yellow/ golden brown pigment derived from hemoglobin, seen within macrophages.

Occurrence

Hemosiderin occurs principally in-

Ø  the red pulp of spleen and other reticuloendothelial systems,

Ø  old hemorrhages into the tissues,

Ø  regressing ovarian corpora hemorrhagica and

Ø  chronically congested lungs.

Hemosiderin responds to prussian-blue reaction that is the common test for iron.

Causes

Ø  Hemolytic anemia,

Ø  Chronic passive congestion of lungs,

Ø  Chronic passive congestion of liver, due to tricuspid valve stenosis or insuffiency.

Chronic passive congestion of lungs is ordinarily caused by abnormalities of heart, valvular insufficiency or stenosis of the left side. As a result, erythrocytes are leaked out from alveolar capillaries into the adjacent alveolar spaces.

These are phagocytized by alveolar macrophages which transform hemoglobin into golden brown pigment, the hemosiderin.

These hemosiderin-laden alveolar macrophages are known as “Heart failure cells”.

Significance

•      The significance of hemosiderosis (deposition of hemosiderin in tissues) indicates that one of the foregoing disorders is present.

•      The presence in large amounts almost always indicates hemolytic anemia.

Hemochromatosis

Hemochromatosis is a condition in which a pigment indistinguishable from hemosiderin is deposited in tremendous amount in

Ø  Cytoplasm of epithelial cells of liver and

Ø  Lesser amounts in several other organs.

Pathogenesis of hemochromatosis involves excessive absorption of dietary iron.

It is accompanied by-

•      cirrhosis resulting from irritation by pigment,

•      diabetes commonly known as “Bronze diabetes” due to deposition of pigment in pancreas,

•      melanin pigmentation of skin.

The cause is thought to be an inborn metabolic defect.

In hemochromatosis, iron-containing pigment does not result from hemolysis; hence, it is different from hemosiderosis.