Not everyone knows that cytology is a science that studies the functions, structure and development of cells of any living organisms, including single-celled ones. For the diagnosis of diseases in humans and animals, cytological studies have become of great importance.
Knowing the definition of what cytology is, it is not at all difficult to understand that this science could develop only after the creation and gradual improvement of the optical microscope and the development of histological research methods.
History of cell discovery
The history of the development of cytology begins with the discovery of the cell. The term "cell" was first used by the Englishman Robert Hooke in 1665, who examined a section of cork under a microscope he had improved. He was able to see the cellular structure of the material, more precisely the cell membranes of cellulose. Later, his discoveries were confirmed by the Italian M. Malpighi and the Englishman N. Gru, and A. Leeuwenhoek in 1781 for the first time published drawings depicting animal cells with nuclei. Thus, cytology, the science of the cell, began to take its first steps.
At the beginning of the 19th century, the idea that the cell is the most important structural unit of any organism began to form, that is, the foundations of cytology were laid. R. Brown in 1831 found nuclei in plant cells, giving them such a name in Latin, and a little later proved that this element is present in the cells of all animals and plants. Scientists have also discovered the process of cell division.
J. Purkinje, who first described the nucleus of an animal cell, came up with methods for clarifying and staining cell preparations, because this is what cytology studies. He introduced the concept of protoplasm and was among the first researchers to attempt to compare animal and plant cells.
In 1839, the Germans T. Schwann and M. Schleiden formulated the cellular theory, where the cell was considered the main element in the structure, development and life of the living world, which contains the whole complex of properties inherent in life, being its basic cell. Since then, it has been established that cytology is the science of all aspects relating to the cell. With the help of cell theory, the nature of various protozoa was revealed. T. Siebold gave a formulation to unicellular animals based on the postulates of cell theory.
For the development of cytology, the emergence of the teachings of R. Virchow on cellular pathology, in which cells were considered as the place where diseases are rooted, became important. Thanks to this, not only physiologists and anatomists, but also pathologists became interested in the study of cells. Virchow also argued that cells only come from their precursors. His teaching strongly influenced the revision of views regarding the nature of cells: if initially the cell membrane was considered the main structural element, then later the cell was defined as a piece of protoplasm with a nucleus inside. Thus, the nucleus was recognized as an integral element of the cellular structure. At the same time, the complex structure of the protoplasm itself was discovered, in which various organelles were found: mitochondria, the cell center, the Golgi complex. Nucleic acids have been found in nuclei.
Video about what cytology studies
The development of cytology was strongly influenced by the laws of inheritance of G. Mendel’s traits and their subsequent interpretation. Thanks to this, the chromosomal theory of heredity appeared, and new directions appeared in cytology – karyology and cytogenetics.
A big step forward for cytology was the invention of the tissue culture method and its derivatives, including:
- single-layer cell culture method;
- the method of culture of fragments and whole organs in animal tissues, on the shells of chicken embryos or in a nutrient medium;
- method of organ cultures of tissue fragments on the section of the gas phase and nutrient medium.
With their help, long-term observations of the vital activity of cells isolated from the body, the study of their division, movement, differentiation, etc. are possible.
The emergence of quantitative methods in cytological studies made it possible to reveal the law of species constancy with respect to cell size, which later became known as the law of constancy of minimum cell sizes. In 1925, the phenomenon of sequential doubling of the volume of cell nuclei was discovered, usually reflecting the doubling of chromosomes in cells.
In the middle of the 20th century, the scientific and technological revolution ensured the rapid development of cytology and the revision of some of its ideas. The creation of an electron microscope made it possible to study the structure and understand the hitherto incomprehensible functions of cellular organelles, as well as to discover a huge number of submicroscopic structures, to understand where stem cells come from.
Types and directions of cytology
When they say what cytology is in biology, they distinguish between general and particular cytology. The first is also called cell biology and is reduced to the study of structures common to most types of cells, as well as their functions, reactions to damage, metabolism, disease changes, recovery processes and adaptation to environmental conditions. Private cytology is aimed at studying the characteristics of specialized cells of multicellular organisms and their adaptation to the environment in the case of protozoa.
Now there are 6 main areas of cytology:
- Cytomorphology studies the features of the cell structure. Its main tools are different types of microscopy of fixed cells (optical, polarizing, electronic) and living cells (luminescent and phase contrast microscopy, dark-field condenser).
- Cytophysiology studies the work of the cell as a living single system, the interaction and functioning of intracellular structures. These complex problems are solved by special experimental methods, combined with the methods of microsurgery, microfilming, and cell and tissue culture.
- Cytochemistry is interested in the molecular structure of the cell and its components, as well as metabolic processes. Optical and electron microscopes, interference and ultraviolet microscopy, autoradiography, cytophotometry, fractional centrifugation with further chemical analysis of each fraction are used for cytochemical studies.
- Cytogenetics is concerned with the regularities of the functional and structural organization of eukaryotic chromosomes.
- Cytoecology studies the response of cells to various environmental factors and the manifested mechanisms of adaptation.
- Cytopathology deals with the study of diseased cells, subdivided into viral (in cases where viruses affect a cell), oncological (changes in tumor cells), cytopharmacology (the effect of drugs), space (cell studies under space flight conditions), etc.
Very often in cytology, a research method is used that coincides with a histological examination, in which a tissue sample is taken from a diseased organ. But there is a difference: a cytological study requires a smaller amount of biomaterial, and its study does not require pre-treatment and special equipment, except for a microscope. The reason for a cytological study may be the undesirability or impossibility of a biopsy, if, for example, the patient is examined in a conventional clinic. With the help of a cytological study, it is possible to assess the state of human integumentary tissues (mucous membranes and skin), since oncological diseases very often begin to form in these tissues. You can also study female hormonal activity, the process of wound healing and other processes.
Video about cytology – the science of the cell
The method of obtaining the material necessary for research depends on which tissue or organ was damaged:
- For skin diseases, prints or scrapings are taken from tissues.
- In diseases of the hematopoietic organs, mammary or thyroid glands, punctates are taken from the affected areas.
- With ailments of the central nervous system, it is necessary to take cerebrospinal fluid.
- In diseases of the lungs, sputum can be collected, etc.
Thanks to the rapid development of science and technology, the possibilities of cytology are constantly growing.