Special histology is the study of tissues and the characteristics of their development, structure, functions and inter-tissue interactions in the composition of organs and organ systems. Organogenesis proceeds on the basis of the interaction of different histogenesis processes, giving rise to structural and functional units of an organ. To designate these units, a number of concepts have been proposed (functional elements, microregions, regions, modules, ensembles, etc.). Since the structural and functional units of organs include cells of different nature and different tissues, it is essential to know tissue specifics, sources of tissue development, stages of histogenesis and regeneration.