Pathological anatomy is a specialty concerned with the study of morphological changes developing in the body as a result of diseases or pathological processes. In this context, pathology is tasked not only with the description of a disease’s morphological causes, but also with revealing patterns of pathological processes emergence and development. This is substantiated by evidence obtained from a variety of medical specialties. Essentially, modern pathological anatomy represents a synthesis of anatomy, histology, biochemistry, normal and pathological physiology, microbiology, genetics, immunology, and molecular biology. This provides an opportunity not only to reveal the morphological underpinnings of a disease, but also to define its association with the bodily dysfunctions and explain their clinical manifestations. Therefore, one can certainly state that it is medical pathology that demonstrates the essence of disease, the morphological changes in the body it causes, and why the dysfunctions of the damaged organs develop, clinically manifesting as symptoms and syndromes. A doctor must understand the causes of specific disease manifestations, and only this knowledge provides a physician with an opportunity to correctly diagnose a disease, predict its course, and treat it.
However, pathological anatomy is a fundamental part of the general science called pathology which explains certain objective laws underlying every disease, and that pathological processes develop according to these laws. Only knowledge of the patterns that the development of pathological processes and diseases follows can empower a doctor in the struggle for human lives. Therefore, to understand the essence of diseases and mechanisms of their development, pathological anatomy should take into account general biological patterns of life on Earth and species-specific reactions including the general reactions of humans as a biological species. Species-specific reactions are inherent in every individual, but in each individual they are refracted through personal individuality (genetic features, reactivity, constitution, etc.). Although all individuals can be affected by specific diseases, in each case the course of the disease will be specific and conditioned by the specifics of the particular patient’s organism and individual reaction to pathological exposure. Thus, pathological anatomy studies general biological and individual patterns of disease development in humans in general, and in each patient in particular. Moreover, it examines specific changes in the morphology of organs and tissues, comparing these with functional disorders inherent to each disease. This scope and importance of the tasks faced by pathological anatomy makes it the theory of medicine. At the same time, this very knowledge makes it a clinical specialty necessary for any hospital to perform lifetime morphological diagnostics, to confirm the appropriateness of performed operations, to analyze clinical errors, and to develop population morbidity and mortality statistics.
In understanding the essence of diseases and pathological processes, pathological anatomy is based on a number of fundamental postulates. It is known that all the reactions of both a healthy and a diseased organism are exceptionally expedient. They are aimed at preserving homeostasis, at maintaining life. Sometimes, in a particular patient, for certain reasons, the body reaction may be insufficient, but as a species-specific reaction it is exceptionally expedient.
Biological expediency also underlies the unity of the body’s physiological and pathological reactions. Reactions that provide vital functioning within the limits of physiological homeostasis may, under pathological conditions, require medical intervention. For example, blood clotting under normal conditions prevents death from blood loss, but the same reaction in atherosclerotic vascular disease leads to formation of thrombi in the cardiac coronary arteries causing myocardial infarction which may be fatal for the patient. Antibody formation as a response to foreign antigen ingress is a basic protective reaction, but in certain circumstances it can lead to the destruction of a host’s tissues, which is the case with autoimmune diseases. Further examples are possible, but their essence remains the same: healthy and pathological conditions are established by the same reactions that acquire other features and biological meanings in disease development, since both health and disease represent life, although in different conditions.
Another important pattern underlying all physiological and pathological reactions of the organism is the dialectic unity of structure and function. Every function is carried out by a definite morphological structure. If there is no such specific material substrate, no specific function is possible. However, implemented by morphological structures, a function consumes a material substrate consisting of those structures, and the organ, tissue, cell, or intracellular components require restoration of this substrate in order to continue functioning. For example, for cardiomyocytes to function, energy must be generated by the mitochondria. After the contractile function is implemented, a portion of the mitochondrial cristae is destroyed, and for cardiac contractions to continue, restoration of lost morphological structures is required. If the destruction of the mitochondria of cardiomyocytes is adequate to their recovery, then cardiac function will be maintained providing blood circulation and vital functions of the body. However, in diseased conditions, the destruction of mitochondria may prevail over their synthesis. In this case, energy depletion of cardiomyocytes develops with further cardiac contractile function insufficiency and cardiac arrest.
Alternatively, a non-functioning organ not vital to the body is subjected to atrophy, i.e. diminishes in size, and its function is decreased. Therefore, structure is inseparable from function, which was figuratively underlined by one of the most prominent Russian physicians V.Kh. Vasilenko: “Function without structure is inconceivable, and structure without function is meaningless”. This implies that no such thing as “functional diseases” is possible. It is obvious that sometimes morphological changes are difficult to reveal using existing research methods, but new methods will be developed, and structural damage will be assuredly detected.
From the provision that implementing function consumes the morphological substrate it follows that maintaining a function is associated with the restoration of the same substrate. Providing it also requires energy and time during which the structure is non-functioning. This leads to a situation where at any moment some part of intracellular structures and cells is destroyed, hence it does not function and is in a state of resynthesis and rest, thus forming a type of organ reserve. The concept of homeostasis itself presumes different intensity of the function within certain limits, e.g., the intensity of a cardiac contraction at rest and under physiological stress. This means that a lower metabolic intensity, lesser amount of energy, and fewer simultaneously functioning structures are required during rest. However, the myocardium needs to have a structural reserve for providing cardiac function intensification within a homeostatic range. Obviously, the possibility of structures functioning at different intensity and with differing consumption of function-providing material substrate is genetically predetermined and possesses a nature of biological regularity, which is referred to as functional and morphological heterogeneity, i.e. non-homogeneity. It is defined by a continuously varying number of actively functioning structures in accordance with the changing environmental conditions and stress levels affecting the organ. Heterogeneity of morphological structures provides a basis for the functional reserve of organs that allows them to function under both physiological and extreme conditions.