Cytology (from cyto- (intestines) and Greek λόγος - study; science; knowledge) is a science that studies living cells and their structure. Cytology can be considered as a kind of cell biology. Cell. The organism as a community of cells is a complex open self-regulating system. The functioning of the body is carried out through cellular processes: growth and development, self-reproduction and differentiation. In this process, everything within the body is processed and reproduced in and out of cells. Therefore, studying the cell at a fundamental level, elucidating the basic mechanisms of functioning of vital systems is a particularly important task, including in relation to humans. The study of elementary structures is necessary not only for understanding biochemical processes. At the microscopic level, you can see defects in their reproduction processes. Examples of such defects include viruses and HIV. In other words, an infection. Another example is diseases that manifest themselves as pathologically altered structure. Microscopy partially allows us to see these pathologies, in particular the eyeball.