Histotopographic and structural features of canine thyroid gland follicles under single dynamic motor loads

The formation of urgent and long-term adaptation of the organism under various modes of motor loads is provided by a change in the activity of the thyroid gland, the functional unit of which is the thyroid follicle. An accurate assessment of the morphological parameters of the follicles of different histotopographic zones of the thyroid gland provides the researcher with objective information about the state of the organ. The purpose of the study was to evaluate the effect of single training, starting and limiting motor loads (treadmill running) on the structural and histotopographic features of the thyroid gland follicles in dogs. On transverse sections of the right lobe of the thyroid gland of dogs, stained with hematoxylin-eosin, the area of the follicles were measured. The measurements were carried out in various histotopographic zones of the gland (central, intermediate, peripheral), distinguished relative to its geometric center. Animals were studied in the control group (16 male dogs) and in the experiment (31 animals), in which, as a result of single motor loads, a different response was formed, manifested in structural and functional changes in the thyroid gland. The studies showed that muscle activity leads to the activation of the functional units of the organ - follicles. The transformation of the thyroid gland as a result of various durations of motor loads is manifested in the obligate involvement of the peripheral zone of the gland, a significant decrease in the area of follicles, an increase in the number of functionally more active follicles of a small area, due to a decrease in the number of predominantly large and medium follicles, and changes in the colloid-epithelial areas ratio. Depending on the parameters of single dynamic motor loads, two ways of primary response of the gland were revealed: either due to a change in the number of follicles of different areas (large, medium, small), or due to a change in their ratio in the histotopographic zones of the organ (central, intermediate, peripheral). Modeling of various parameters of motor loads can be used to analyse its of the influence the structural reorganization of the thyroid gland in the experiment. The constant structural variability of the peripheral zone found in the present study may be associated with special conditions of blood supply from the gland capsule.