The purpose of the work was to study the histological structure of the greater omentum in the people of second mature and elderly age in normal condition and in peritonitis. Materials and methods. The materials of the study were 40 greater omenta of deceased people (20 males and 20 females) of the second mature and elderly age without pathology in the abdominal cavity and 10 greater omenta of deceased people from peritonitis taken in accordance with the cooperation agreement. Pieces of greater omenta were fixed with a 10% solution of neutral formalin. Paraffin blocks were made according to the traditional method, followed by making sections that were stained with hematoxylin and eosin. Histological specimens were studied using a light microscope "MICROmed" XS-3320 in transmitted light using an increase of ×40, ×100, ×400 with the photographing of micropreparations on the camera Ningero Sheng Heng Optics and Electronics Co. Results and discussion. The findings of the study showed that the histological structure of the tissue of the greater omentum in women and men of these ages has common structural features. Histological sections stained with hematoxylin and eosin revealed that normally the outside of the greater omentum is covered with a solid layer of mesotheliocytes, located on the basal plate, deeper there were “milk spots”, white adipocytes, which formed individual fat particles, separated by connective tissue fibers. “Milk spots” do not have capsules, in contrast to lymph nodes, and contain lymphocytes and macrophages that emerge from their fenestrated postcapillary venules and migrate into the abdominal cavity through “stigmas”. Normally, active and inactive “milk spots” are present in the greater omentum in adults. “Milk spots” had an oval, irregular and spherical shape and different sizes. In the thickness of the tissue of the greater omentum there were lymph nodes, which, in contrast to the "milk spots" on the outside were covered with a connective tissue capsule. In the thickness of the nodule, trabeculae extend from the capsule. Marginal and medullary sinuses were determined. Lymphocytes were the main cellular component of lymph nodes. Conclusion. In peritonitis, disruption of the continuous mesothelial cover of the greater omentum, resulted from disintegration of mesothelial cells; some areas of their adhesion and desquamation were observed. Areas with inflammatory infiltration, plethora of arterial and venous microvessels and an increase in active “milk spots” with a high content of lymphocytes were found in the fat particles of the greater omentum

Keywords: greater omentum, “stigmas”, “milk spot”, macrophages, lymphocytes

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