Hemoglobin-derived pigment accumulations. Hemosiderosis. Types of jaundice.
So, pigments can be Exogenous (from outside the body, such as Carbon) or Endogenous (from within the body. Endogenous pigments can then be broken down into:
- Hemoglobin derived organic pigments (Hemosiderin, bilirubin)
- Non Hemoglobin derived pigments (Melanin, Lipofuscin)
Hemoglobin consists of Globin (with 2 alpha and 2 beta chains) and Heme, a protoporphyrin with an iron chelate. This in turn can be broken down into two pigments, Hemosiderin and Bilirubin.
Hemosiderin is only found within cells and is a complex of ferritin (stored iron) and other material. Where the body has excess iron it can lead to an alteration of cellular colour visualized by light microscopy. The dominating colour is golden yellow to brown. Build up of hemosiderin can be a product of local or systemic excess iron.
Remember: Hemosiderin is the only common brown pigment that turns blue-black with Perls' Prussian blue stain (it reacts with iron). This separates it from lipofuscin and melanin, which look similar on H&E. Example: 'heart failure cells' – hemosiderin-laden macrophages in the alveoli in chronic left heart failure.
Systemic build up can be a product of:
- Increased iron absorption
- Impaired iron utilization
- Hemolytic anemias (early degradation of RBCs)
- Transfusions
The most obvious build up of systemic hemosiderin is in the mononuclear phagocytes of the liver, bone marrow, spleen and lymph nodes.
Perls Prussian blue stain, liver: hemosiderin in a Kupffer cell (a mononuclear phagocyte) turns blue; lipofuscin in the neighbouring hepatocyte stays brown.
Image: “Kupffer cell with hemosiderin and hepatocyte with lipofuscin, iron stain” by Mikael Häggström , M.D. Author info - Reusing images - Conflicts of interest: None Mikael Häggström , M.D. Consent note , CC0, via Wikimedia Commons.
Meanwhile, excess local iron can be as a result of a hemorrhage, such as a bruise, where the sudden lysis of a large number of RBCs creates a large amount of iron, which is consequently stored as hemosiderin.
Finally in relation to Hemosiderin, there are a number of genetic disorders which cause the body to accumulate excess iron, with mutations to the HFE gene on chromosome 6 leading to poorly regulated iron levels and deposition of hemosiderin throughout the body.
Secondly, Bilirubin is the end product of heme degradation. Normal bilirubin production is approximately 0.2-0.3 gm/day and is derived from the breakdown of erythrocytes. The process of production is as follows: