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Close concept: ikterus
Jaundice, yellow coloring of integuments and scleras, results from accumulation of bilirubin in blood serum and its subsequent adjournment in hypodermic fabrics. The English word Jaundice comes from the French jaune which means yellow, and the word "ikterus" has the Greek origin and means yellow color.
The general bilirubin of blood serum defined in clinical laboratories by chemical methods can be divided into the related and untied fractions. Synonyms of untied bilirubin are the indirect or delayed bilirubin, and connected — direct, immediate, fast or "one-minute" serumal bilirubin. In the majority of hospital laboratories continue to use terms an indirect bilirubin for designation of untied fraction and a straight line — for connected.
Normal limits of the general bilirubin of blood serum fluctuate from 3,4 to 20,5 µmol/l. Usually the fraction of direct bilirubin makes less than 15% of the general or from 0 to 3,4 µmol/l at the upper bound of norm for the indirect fraction making 17,1 µmol/l. Usually jaundice cannot be found visually until the general serumal bilirubin does not exceed 51,3 µmol/l. Jaundice with the high content of bilirubin in blood can be passed during survey of the patient at dim scattered lighting, and also in the room with yellow or brownish coloring of walls. For identification of early stages of jaundice of the patient it is recommended to examine at a daylight.
Bilirubin is formed as a result of degradation of a porphyrinic ring gem after the grown old erythrocytes collapse in bodies of reticuloendothelial system, and at destruction of 1 g of hemoglobin about 36 mg of bilirubin are formed. Besides, bilirubin is a by-product of the hemolysis (a so-called inefficient erythrogenesis) happening in marrow and disintegration of a porphyrinic component of tsitokhromoksidazny system of cells of a liver. The last is often designated the term "early peak", it makes from 15 to 25% of the bilirubin which is formed in physiological conditions. Turnover of bilirubin in an organism makes about 40 mg/kg/days.
Gem is an initial product of degradation biliverdin, a green water-soluble pigment. In the beginning from a porphyrinic ring one carbon atom of which in the subsequent carbon monoxide is formed is chipped off - it is the only endogenous reaction in a human body leading to formation of carbon monoxide. Further biliverdin turns into bilirubin which is insoluble in water and which excretion is possible in its connection with other substances. As bilirubin does not possess polarity, it is transported by blood in connection with albumine, and delivery of bilirubin to cells of a liver depends on a hepatic blood-groove. Cells of a liver contain the specific proteins connecting bilirubin (ligandina) which promote bilirubin capture by hepatocytes. After intake of bilirubin in liver cells one molecule of glucuronic acid joins it in the presence of the catalyst of an uridindifosfatglyukuroniltransferaza. The end product of this reaction, bilirubinmonoglyukuronid, then is exposed to a transglyukuronization with other molecule of a bilirubinmono-glucuronide therefore also free bilirubin is formed bilirubindiglyukuronid. Bilirubindiglyukuronid is actively excreted through a canalicular membrane of bilious channels and comes to bile. In physiological conditions more than 95% of bilirubin of bile are provided bilirubindiglyukuronidy.
Bilirubin passes several stages of recovery which end products are various forms of urobilinigen, pigments giving to Kalou characteristic brown coloring in a digestive tract. Urobilinigen is soluble in water, can be soaked up in intestines and repeatedly be excreted by a liver. This process received the name of an intra hepatic cycle of urobilinigen. Stages of a metabolism of bilirubin are shown on rice.
Main stages of formation of bilirubin.