General Principles of Organizing the Whole Organism
For a multicellular organism to function as a single unit, evolution has developed basic management principles. These include reflex responses, self-organization, autoregulation, as well as mechanisms of correlation and regulation. All these tools did not arise instantaneously—they were thoroughly perfected and consolidated over a long evolutionary process.
Correlation represents an interaction between elements of a living system in which they combine to create an entirely new quality. At the same time, each participating element fully retains its initial, uniquely inherent functions. This is the baseline level of coordination, without which more complex regulation—a process where one structure clearly subordinates another to achieve the global goal of the whole organism—is impossible.
Types of Correlative Connections
Correlative connections are generally divided into two large groups depending on their origin:
- Mechanical correlations. These arise during the direct physical interaction of actively working organs. A classic example of such cooperation is the combined work of the heart and lungs. Similarly, abdominal organs interact: the intestine is closely mechanically connected with the adjacent liver and stomach.
- Chemical correlations. In this case, the connection is provided by specific mediator substances and biologically active compounds. The crucial role of chemical correlation manifests as early as embryogenesis: it is what guides the growth of nerve fibers strictly toward the innervated organ. This same mechanism is critically important for the restoration (regeneration) of nerves after injuries or surgical operations.
Chemical correlation can be implemented in two ways:
- Contact pathway. Adjacent areas of neighboring cell membranes form so-called gap junctions (fusion zones). Through them, a direct exchange of cellular protoplasm and biologically active substances occurs.
- Distant pathway. Implemented over a distance through the body's fluid media. Biogenic amines and protein-nature substances (hormones, oligopeptides) act as transmitters.
Three Modes of Functional Regulation
When it comes to the targeted subordination of structures, three main modes of control operate in the body:
- Nervous regulation. Implemented exclusively by the nervous system. Its main distinguishing feature is colossal speed. Nervous influences occur very rapidly.
- Humoral regulation. Occurs via chemical substances circulating in internal fluid media: blood, lymph, tissue fluid, and cerebrospinal fluid. Hormones, cytokines, oligopeptides, immune factors, neurotransmitters, and other biologically active substances act as regulatory factors here. Unlike nerve signals, humoral influences are relatively slow.
- Neurohumoral regulation. This is a combination of the two previous pathways. It serves as the primary form of regulation in the intact organism.
Mechanisms of Neurohumoral Interaction
Neurohumoral regulation demonstrates how nervous and humoral mechanisms complement each other. Interaction between them follows two main scenarios.
First mechanism: primary action of humoral factors on neural centers. Humoral agents circulating in fluids affect the central nervous system (CNS). Then the CNS secondarily, via neural pathways, sends signals to peripheral organs.
Second mechanism: simultaneous influence on an organ. In this situation, the target organ receives commands simultaneously through both channels. Neural influences are implemented rapidly but act briefly, providing an immediate response. Humoral influences arrive later, yet act more persistently, maintaining function at the required level.