Scientific heritage of Ivan Petrovich Pavlov
In the scientific heritage of Pavlov there are three major areas: the physiology of blood circulation, the physiology of digestion, and the physiology of higher nervous activity.

Issues of regulation and self-regulation of blood circulation occupied Ivan Petrovich from his student years. Pavlov put forward the very idea of self-regulation of blood circulation. He proved that the mechanisms of the cardiovascular system maintain blood pressure at normal levels. Later, this idea developed into a large theory of self-regulation of the functions of almost all organs and systems.

Ivan Petrovich showed the presence of a complex of regulatory nerves in the heart and established the trophic nature of these influences. Later Pavlov drew attention to the centers of accumulation of nerve endings in the vessels and a number of visceral organs and suggested the presence of a special centripetal system. Later Academician Vladimir Nikolaevich Chernigovsky developed this idea into an independent doctrine of interoception. Already at this stage of Pavlov’s work, the desire to study the whole organism in all its manifestations was clearly manifested.

The second direction of Pavlov’s scientific work is the physiology of digestion. It brought him worldwide fame and the Nobel Prize. The prize was awarded "for work on the physiology of digestion, which has led to a clearer understanding of the vital aspects of this issue." The essence of the discovery is an understanding of the mechanisms of nervous regulation of digestion. Pavlov began research in this area at the university, and conducted systematic research at the Institute of Experimental Medicine.

The scientist practically re-created a full-fledged method of chronic experiment and carried out a series of subtle operations on dogs: the imposition of original fistulas of the ducts of the salivary glands, pancreas, gallbladder etc.

Obtaining pure gastric juice became possible when Pavlov and Ekaterina Olimpovna Shumova-Simanovskaya in 1889 added esophagotomy to the imposition of a gastric fistula — cutting the esophagus. It was this operation that made it possible to carry out the experiment of imaginary feeding and study the mechanisms of the work of the gastric glands.

The method of sham feeding itself did not allow a complete study of gastric secretion under normal conditions. Therefore, Pavlov improved the method of the small ventricle, introduced into the practice of the physiological experiment by Rudolf Heidenhain. Ivan Petrovich was able to create a small stomach, which was identical to the main one in functionality, but did not allow food to enter its cavity.

Pavlov considered the activity of the digestive system as a chain of successive processes: with the beginning of the act of eating, the separative work develops and spreads along the alimentary canal due to the adhesion of one digestive instance to another.

The third direction — the physiology of higher nervous activity — became the main legacy of Pavlov.

The scientist chose the salivary gland as an object of research. She actively responds to food-related irritations that act at a distance from the body.

Pavlov called the usual food reaction upon contact with a food stimulus an unconditioned reflex. It is inherent in all animals. A similar food reaction under the action of the same food factors remote from the body is a conditioned reflex. Conditioned reflexes include sight, smell, and environment. Conditioned reflexes are developed under certain conditions based on personal experience and are individual. In higher animals, they are carried out with the participation of the cerebral cortex, although subcortical structures can also be involved in the closure of the conditioned connection.

Pavlov’s method of conditioned reflexes made it possible to establish that the processes of excitation and inhibition are the basis of the activity of the cerebral hemispheres, and to describe in detail the interaction of these processes in the cerebral cortex. All this served as the basis for creating an idea of the analytic-synthetic nature of higher nervous activity, describing the three types of the nervous system — balanced, excitable and inhibitory, as well as four types of temperament, determining their criteria and differences.

Pavlov considered the concept of "higher nervous activity" to be equivalent to the concept of "behavior" or "mental activity". He believed that the conditioned reflex, with all its universality, develops, the number of its forms and the level of perfection are constantly growing. This led to the appearance in a person of a qualitatively new type of signaling — speech, in which a word acts as a signal of objective, or primary, signals. Ivan Petrovich called this qualitatively new form of signaling the second signaling system of reality and considered it a product of social life and human labor activity. The second signaling system is the basis for the implementation of the most complex abstractions and thinking.

For many years, Pavlov experimentally studied the pathology of higher nervous activity as well as nervous and mental diseases of humans, on dogs.