Biological Chemistry - Berezov, T. T., & Korovkin, B. F. 1998

Liver
Bile

Bile is a yellowish-brown liquid secretion produced by hepatic Cells. The Human Body produces 500–700 ml of bile per day (10 ml per 1 kg of body weight). Bile formation occurs continuously, although its intensity fluctuates sharply throughout the day. Between periods of Digestion, hepatic bile flows into the Gallbladder, where it becomes concentrated through the reabsorption of Water and electrolytes. The specific gravity of hepatic bile is 1.01, whereas that of gallbladder bile is 1.04. The concentration of major components in gallbladder bile is 5–10 times higher than in hepatic bile (Table 16.3).

Class="center">Table 16.3. Concentration of major components in human bile

It is hypothesized that bile formation begins with the active secretion of water, bile acids, and bilirubin by hepatocytes, resulting in The formation of so-called primary bile within the bile canaliculi. As this primary bile flows through the bile ducts, it comes into contact with Blood Plasma, establishing an electrolyte equilibrium between the bile and plasma. This indicates that bile formation involves primarily two mechanisms: filtration and secretion.

Hepatic bile substances can be divided into two groups. The first group comprises substances whose concentrations in bile differ only slightly from their levels in blood plasma (e.g., Na⁺ and K⁺ ions, creatinine, etc.), which to some extent Supports the existence of a filtration mechanism. The second group includes compounds whose concentrations in hepatic bile are many times higher than in blood plasma (bilirubin, bile acids, etc.), pointing to an active secretory mechanism. Recently, accumulating evidence has highlighted the predominant role of active secretion in bile formation. In addition, several Enzymes have been detected in bile, most notably alkaline phosphatase of hepatic origin. During impaired bile outflow, The activity of this enzyme in blood serum increases.

Main Functions of bile. Emulsification. Bile acid salts possess The ability to significantly reduce surface tension. This enables them to emulsify fats in the intestine and dissolve fatty acids and water-insoluble soaps. Acid neutralization. Bile, with a pH slightly above 7.0, neutralizes the acidic chyme coming from The Stomach, preparing it for intestinal digestion. Excretion. Bile is an essential vehicle for excreting bile acids and cholesterol. Furthermore, it eliminates numerous medicinal substances, toxins, bile pigments, and various inorganic elements such as copper, zinc, and mercury from the body. Cholesterol solubilization. As noted, cholesterol, like Higher Fatty Acids, is a water-insoluble compound that remains dissolved in bile solely due to the presence of bile salts and phosphatidylcholine. When bile acids are deficient, cholesterol precipitates, which may lead to gallstone formation. Typically, gallstones feature a pigmented inner core consisting of protein surrounded by the core. Most commonly, the core is surrounded by alternating layers of cholesterol and calcium bilirubinate. Such stones contain up to 80% cholesterol. Intensive stone formation is observed during bile stasis and infection. Stasis-induced stones may contain 90–95% cholesterol, whereas infection-related stones often consist of calcium bilirubinate. It is generally accepted that the presence of Bacteria increases the ß-glucuronidase activity of bile, leading to the Cleavage of bilirubin conjugates; the liberated bilirubin then serves as a substrate for stone formation.