The liver has a lot of functions: it transforms extrinsic (alimentary) amino acids, carbohydrates, lipids, and vitamins; it synthesizes serum proteins, bile, detoxifies endogenous metabolic products, xenobiotics, and excretes them into bile. 95-99% albumins, almost all α-globulins, and the main amount of plasma β-globulins are synthesized in the liver. Participation of hepatocytes in lipid and basal metabolism consists in synthesis of LP, glycoproteins, cholesterol phospholipids, bile, and higher fatty acids. The liver maintains normal glucose concentration in blood by synthesizing glycogen, as well as via gluco- and neoglucogenesis. It contains stellate endothelial (Kupfer) cells that constitute more than a half of all tissue macrophages; together with hepatocytes and endothelial cells, they play a key role in eliminating various toxic substances and microbes from the blood delivered via the portal vein and the hepatic artery. Steroid hormones (glucocorticoids, mineralocorticoids, androgens, estrogens), iodine-containing thyroid hormones, vasopressin, insulin, serotonin, histamine are also destroyed in the liver. The liver deposits fat-soluble vitamins (A, D, E, K), it also activates vitamin D (25-hydroxylation). It is also responsible for hemopoiesis during the intrauterine period.
The structural-functional unit of the liver is a rhomboid hepatic acinus formed by segments of adjacent classic hexagonal lobules. Terminal hepatic venules are located near its acute angles, while triads of portal tracts, along which sinusoids spread inside the acinus, are near its blunt angles (fig. 13.1). The blood flow in the acinus is directed from the first to the third zone. The hepatic acinus is divided into 3 zones:
- zone 1 (periportal), where hepatocytes receive blood rich in nutrients and oxygen; they are more metabolically active than parenchymatous cells of other zones;
- zone 2 (median or intermediate);
- zone 3 (perivenular) is located far from other zones of axial vessels.
A wide spectrum of damaging exposures can impair the hepatic function. These include metabolic, toxic, infectious, circulatory factors, as well as tumors. Hepatic diseases are often rather varied. They can be congenital and acquired, primary (e.g., in viral hepatitis) and secondary in generalized disorders (tuberculosis, sepsis, alcohol disease, tumors of other locations). The intensity of clinical and laboratory syndromes often is not always consistent with the severity of hepatic morphological disorders. The accurate diagnosis may be established only using intravital morphological study: liver biopsy.
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Fig. 13.1. Structure of hepatic acinus: PT - portal tract; THV - terminal hepatic vein; 1-3 - areas of hepatic acinus