The thymus is the central organ of T-lymphocytopoiesis, in it the formation of T-lymphocyte 12 precursor cells and a number of thymic hormones occurs. Structural and functional 13 rearrangements of the thymus under the influence of the temperature factor are characterized by 14 cyclicity, where periods of early changes, peak and distant changes are distinguished. Each of the 15 periods is characterized by its own characteristics, which determine the essence of the organ's 16 adaptive rearrangements in response to temperature exposure