Direct and free bilirubin

Bilirubin exchange

The respiratory function of the blood provides all body tissues with the necessary amount of oxygen carried by a highly specialized transporter - hemoglobin - in the structure of red blood cells. However, these cells have a limited lifespan of an average of 100-120 days. Then they enter the organs of hemorrhage, where hemoglobin is released from them. It is immediately bound by haptoglobin and transported to the cells of the reticuloendothelial system for further transformation into a non-toxic pigment (direct bilirubin) and excretion with bile. In macrophages and histiocytes, hemoglobin initially decomposes to biliverdin, which is 4 pyrrole rings connected by methane bridges. And then it is restored to free bilirubin, which is captured by transporter proteins and transferred to the liver. In its parenchyma, it is converted into direct bilirubin, that is, glucuronate binding to neutralize it.

The role of bacteria

An indispensable role in further reactions to the secretion of bile pigments is the normal intestinal microflora. Direct bilirubin from the liver is collected as part of bile in vesica fellea, and upon opening the Vater nipple enters the duodenum, and then into the small intestine, where it is freed from glucuronic acid and converted into stercobilinogen, excreted in feces. Part of it, when passing through the rectum, is absorbed into the hemorrhoidal veins that enter the general bloodstream, bypassing the liver, and is excreted through the kidneys with urine. Thus, both free and direct bilirubin are constantly detected in the blood. The norm of the latter is about 5.1 μmol / l, and the total is 15.

Diagnosis of liver disease

The fluctuations and the ratio of these indicators can be judged on the functioning of the liver.

So, if the parenchyma of this organ has an infectious or toxic lesion, then most of the free pigment remains unbound, and the concentration in the blood of both forms of pigment increases sharply. Direct bilirubin is detected in the blood with so-called subhepatic jaundice, in which there are obstacles to the normal outflow of bile, and in this regard, bile regurgitation into the general bloodstream occurs. The reason for this may be compression of the bile duct by a tumor of the head of the pancreas, stone obliteration, etc. There is also suprahepatic jaundice, the cause of which is the increased breakdown of hemoglobin in the bloodstream. Hemolytic toxins of microorganisms and poisons, some physiological conditions can affect this. However, with all these types of hepatitis, bilirubin accumulates in the tissues. Unbound due to its lipophilicity, it easily penetrates into cells, including through the blood-brain barrier, and disconnects the electron transfer chains in mitochondria, thereby inhibiting energy metabolism. Safer in this regard is direct bilirubin, the norm of which is non-toxic, since its molecules are insoluble.