| Summary: | Features of histoarchitectonics, cyto- and histometry of mesenteric lymph nodes in ruminants (cattle, sheep) and horses have been clarified. Scientific studies show that the histoarchitectonics of mesenteric lymph nodes in experimental animals are similar but differ in certain morphometric parameters. Lymph nodes are covered with a connective tissue capsule. Its thickness in cattle 1.7 fold greater than the thickness in sheep and horses. The parenchyma of the lymph nodes is formed by cortical and cerebral substances, the boundary between which is clearly expressed on the section of lymph nodes. According to the analysis of morphometric studies, the cortex is more developed in sheep (55.14±16.7%), the brain – in horses (68.6±6.83%). However, the average area of lymph nodes in sheep (0.19±0.05 mm2 ) and horses (0.08±0.01 mm2) is much smaller than in cattle (0.46±0.07 mm2). The cytostructure of lymph nodes is represented by various cellular elements, the most pronounced of which are blast forms, lymphocytes, reticular cells, macrophages, which differ in their structure and intensity of staining. In the lymph nodes of mesenteric lymph nodes in cattle, small and medium lymphocytes (47.1±2.53% and 31.7±1.84%) occupy a significant share. In large numbers, they are located on the periphery of lymph nodes with pronounced light centers. Reticular cells are 14.6±1.37%. Lymphoblasts and large lymphocytes, which are mainly localized in the light centers of the lymph nodes, occupy 3.8±0.87%, and macrophages – 1.4±0.3%. The proportion of destroyed cells is 1.0±0.26%. The main part of the cerebral substance is occupied by pulp cords. There is a tendency for small lymphocytes to increase, mainly due to a 3.1-fold decrease in the number of blasts and large lymphocytes, a 3-fold decrease in the number of macrophages, and a two-fold decrease in the number of destroyed cells. The number of average lymphocytes and reticular cells is almost unchanged compared to the same indicators in the lymph nodes and is 31.0±2.48% and 13.8±1.5%. A similar distribution of cellular elements in the lymph nodes and lymph nodes was observed in sheep and horses. However, in sheep, in contrasts to cattle, there was a 1.4-fold increase in the number of blasts and large lymphocytes in the lymph nodes and 1.6-fold in the pulp. In horses, these figures have not changed. An increase in the cytopopulation of reticular cells was observed, especially in pulp cords from 13.8±1.5% in cattle to 23.0±1.73% in sheep and to 21.1±0.9% in horses. The number of macrophages remained almost at the same level as in cattle. The percentage of destroyed cells in ruminants was almost the same, but in horses, this figure increased 1.8 fold in the lymph nodes and decreased 2.5 fold in the pulp, relative to such figures in cattle
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