Part ll CYTOLOGY

Cytology is the study of general patterns of cell development, structure, and functions. The first general ideas of the cell structure were postulated by J.B. Carnoy in 1884 in his book "La Biologie Cellulaire". In the 20^th century, cytology (cell biology) became a separate scientific discipline studying the development, structure and functions of the cell.

The cell (from the Latin word cellula) is a membrane-limited microscopic living system consisting of the nucleus and the cytoplasm characterized by irritability, reactivity, ability to regulate the composition of its internal environment and reproduce. The cell is the basic developmental, structural and functional unit of all animal and plant organisms (Fig. 4.1). As an isolated unit of life, it bears all the properties of an independent organism. But at the same time in multicellular organisms, it becomes a structural and functional part of the whole. A unicellular organism consists of a single cell, whereas in multicellular organisms we can distinguish somatic cells, which form the body, and germ cells which are responsible for reproduction.

Modern cytology can be described as the study of nature and phylogenetic connections of cells, principles of their functioning and special qualities. It should be noted that cytology is of great importance to medical sciences. Pathological changes in cells usually reveal themselves earlier than the symptoms of the disease; they are characterized by different degree of manifestation, which determines the severity of the illness and its outcome. In the process of recovery, a complete or partial restoration of the cell functionality takes place. Some cytologic examinations are very important for modern diagnostics and therapy; they include blood and bone marrow test, cerebrospinal and pleural fluid analysis, karyotyping using cell cultures for testing medical substances, etc. The cloning method allows creating and using cell stocks of healthy cells to restore the structure and functionality of the organs affected by the illness.

Despite significant achievements in modern-day cell biology, the cell theory remains crucially important.

In 1838, German zoologist T. Schwann was the first to indicate the homology, or likeness, of plant and animal cells. Sometime later he formulated his cell theory of organisms. Since T. Schwann actively used the observations of botanist M. Schleiden when developing the theory, the latter is rightfully considered a co-author of the theory. According to the main tenet of the theory, the cell is the structural and functional unit of all living organisms.

In the end of the 19^th century German pathologist R. Virchow revised and complimented the theory with an important deduction of his own. In his book

Fig. 4.1. Schematic representation of the animal cell: 1 - nucleus; 2 - cytoplasm; 3 - microvilli; 4 - ribosomes; 5 - rough endoplasmic reticulum; 6 - smooth endoplasmic reticulum; 7 - the Golgi apparatus; 8 - lysosome; 9 - mitochondria; 10 - centrosome; 11 - microtubules; 12 - desmosome (according to N.B. Khristolyubova, 1962, altered version)

"Cellular Pathology as Based on Physiological and Pathological Histology" (1855-1859) he substantiated the fundamental statement of the cell development continuity. Unlike Schwann, Virchow defended the view that the new cells never originate from a structureless living substance - cytoblastema, but always by existing cell division (from the Latin word omnis cellula e cellula). Pathologist L. Barr from Lyon emphasized the specificity of tissues by adding: «Cell derives from the cell of the same nature».

It is worth mentioning that 100 years later the core provisions of the cell theory were revised based on the works of O.B. Lepeshinskaya. Her book "Origin of Cells from Living Matter and the Role of Living Matter in the Organism" was awarded