Ultrastructural organization of the wall sinusoidal hemocapillary of the liver in intact white rat

Background. The liver is a vital organ for many physiological processes, playing a major role in metabolism, detoxification, plasma protein synthesis and nutrient storage, immunity, and it can only perform its many functions if there is an adequate blood supply to the liver cells. Objective: to study the ultrastructural organization of the wall sinusoidal hemocapillary of the liver intact white rat. Methods. Experimental studies were conducted on 10 sexually mature white male outbred rats weighing 180-230 g. The experiments were carried out in compliance with moral and ethical standards in accordance with the provisions of the European Convention for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes (Strasbourg, 1986), Council Directive 2010/63/EU, and Law of Ukraine No. 3447-IV ‘On the Protection of Animals from Cruelty’. All rats were on a standard diet designed for laboratory animals and had free access to water - ad libitum. During the 10 days of quarantine, daily observations were made of the animals' appearance, behaviour, food intake and general condition. The material for electron microscopic examination was obtained immediately after the rats were withdrawn from the experiment and sections were prepared according to the generally accepted method. Ultrathin liver sections were examined and photographed using a transmission electron microscope PEM-100-01 (Ukraine), accelerating voltage - 75 kV, magnification ×1500-×40000. Results. Electron microscopic examination demonstrates the presence of gaps and fenestrae in the sinusoid wall; thus, the endothelial lining is not continuous. The combination of discontinuity with the absence of a basement membrane in the sinusoid is a unique feature of the fine structure of the liver and corresponds to its functions. Based on electron microscopic examination, several types of cells were differentiated: endothelial, Kupffer cells, fat-storing cells (Ito cells) and pit cells, which are characterized by differences in ultrastructure, and location, which confirms their wide functional capabilities. Special attention is paid to the ultrastructural features of the nuclei and cytoplasm of endothelial cells and Kupffer cells and their relationships. Conclusion. The identified features of the ultrastructural organization of the sinusoidal capillaries of the liver are important for establishing a standard basis and subsequently for comparison with the detected changes obtained in experimental models of induced pathologies.