Mixed Dystrophies and Complex Proteins
To understand the mechanisms underlying haemosiderosis and haemochromatosis, it is necessary to examine the concept of mixed dystrophies. These are pathological processes involving quantitative and qualitative structural changes in tissues. Their main distinguishing feature is the totality of the lesion. Metabolic disorders do not occur in isolation, but simultaneously in the three critical components of any organ:
- In the parenchyma (specific functional cells).
- In the stroma (connective tissue supporting framework).
- In the vessel walls (structures ensuring blood supply).
The essence of this pathological process is that metabolic products of complex proteins, or proteids, begin to accumulate in excess within the cells themselves and in the surrounding intercellular matrix. In anatomical pathology, there are three main groups of such complex proteins: chromoproteins, nucleoproteins, and lipoproteins. The disorders discussed here are directly related to impaired metabolism of the first group—pigmented proteins.
Disorders of Pigment Metabolism
Pigments are specific colored substances whose accumulation visually and structurally alters affected tissues. Pigmentary metabolic disorders are always associated with the excessive accumulation of these compounds. By origin, all pigments are divided into two broad categories: exogenous (entering the body from the external environment) and endogenous (synthesized within the body itself).
The largest and clinically most significant group of endogenous pigments is haemoglobin-derived pigments. As the name implies, all of them are various derivatives of haemoglobin. Haemoglobin itself is a high-molecular-weight chromoprotein. Its molecule has a complex structure and consists of two inseparable components: an iron-containing moiety (called haem) and a protein base (called globin). The breakdown and transformation of this molecule give rise to all other pigments in this group.
Classification of Haemoglobin-Derived Pigments
In anatomical pathology, haemoglobin derivatives are strictly classified according to a single key biochemical feature: the presence or absence of iron molecules in their structure.
Iron-containing pigments (Fe+):
- Haemoglobin (base chromoprotein);
- Ferritin;
- Haemosiderin (the pigment whose excess causes haemosiderosis);
- Haematins.
Non-iron-containing pigments (Fe-):
- Bilirubin;
- Haematoidin;
- Porphyrins.
It is essential to understand the difference between the physiological and pathological presence of these substances in tissues. Normally, a healthy body always contains haemoglobin, ferritin, haemosiderin, and bilirubin. However, the appearance of pigments such as haematoidin, haematins, and porphyrins is an absolute marker of pathology—they are absent in healthy tissues.
Haemochromatosis as an Extreme Form of Disorder
Haemochromatosis (haemochromatosis) represents an extremely severe form of chromoprotein metabolism disorder. According to strict pathomorphological criteria, this pathology is diagnosed when the total iron content in the human body exceeds the critical threshold of 15 grams.
This massive iron overload leads to extensive quantitative and qualitative structural changes. The excess of iron-containing pigments infiltrates the parenchyma, stroma, and vessels, fitting the classic morphological pattern of severe mixed dystrophy.