Exchange of bilirubin
The respiratory function of 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, an average of 100-120 days. Then they enter the blood-destruction organs, where hemoglobin is released from them. It is immediately bound by haptoglobin and transported to the cells of the reticuloendothelial system for further conversion to a nontoxic pigment (bilirubin direct) and excretion with bile. In macrophages and histiocytes, hemoglobin initially decomposes to biliverdin, which is 4 pyrrole rings bound by methane bridges. And then it is restored to free bilirubin, which is captured by protein-transporter and transferred to the liver. In its parenchyma, its transformation into bilirubin is direct, that is, the binding by glucuronate for its neutralization.
The role of bacteria
An irreplaceable role in further reactions to release bile pigments is performed by the normal intestinal microflora. Bilirubin direct from the liver is collected in the bile in the vesica fellea, and when the Fater's nipple is opened, it enters the duodenum, and then into the small intestine, where it is freed from glucuronic acid and turns into sterocilinogen, which is released from the feces. Part of it when passing through the rectum is absorbed into the hemorrhoid veins that enter the general bloodstream, bypassing the liver, and is excreted through the kidneys with urine. Thus, in the blood, both free and direct bilirubin are constantly detected. The norm of the latter is about 5.1 μmol / l, and the total - 15.
Diagnosis of liver diseases
By fluctuations and the ratio of these indicators, one can judge the functioning of the liver. So, if the parenchyma of this organ has an infectious or toxic damage, most of the free pigment remains unbound, and the concentration in the blood of both forms of pigment increases dramatically. Bilirubin is detected in the blood in the so-called subhepatic jaundice, in which there are obstacles to a normal outflow of bile, and in connection with this there is a regurgitation of bile in the total blood flow. The cause of this may be compression of the bile duct with a pancreatic head tumor, stone obliteration, etc. There is also superhepatic jaundice, the cause of which is the increased disintegration of hemoglobin in the bloodstream. This can be influenced by hemolytic toxins of microorganisms and poisons, some physiological conditions. However, for 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 the mitochondria, thus inhibiting the energy metabolism. Safer in this regard bilirubin is straight, the norm of which is non-toxic, since its molecules are insoluble.