General principles of building the whole organism
For a multicellular organism to function as a single entity, evolution has developed basic control principles. These include reflex reactions, self-organization, self-regulation, as well as mechanisms of correlation and regulation. All these tools did not arise instantaneously—they were thoroughly refined and consolidated in the course of a long evolutionary process.
Correlation is an interaction of the elements of a living system in which they combine to create an entirely new quality. Meanwhile, each participating element fully retains its initial, intrinsic functions. This is the baseline level of coordination, without which more complex regulation—a process where there is already explicit subordination of one structure to another to achieve a global goal for the entire organism—is impossible.
Types of correlative connections
Correlative connections are usually divided into two major groups depending on the nature of their origin:
- Mechanical correlations. These arise during the direct physical interaction of actively functioning organs. A classic example of such cooperation is the joint work of the heart and lungs. Similarly, the abdominal organs interact: the intestine is closely mechanically linked to the adjacent liver and stomach.
- Chemical correlations. In this case, the connection is provided by specific "messenger" substances, which include neurotransmitters and biologically active compounds. The crucial role of chemical correlation is manifested 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 regions of the membranes of neighboring cells form so-called gap junctions (fusion zones). Through these, a direct exchange of cellular protoplasm and biologically active substances takes place.
- Distant pathway. Carried out at a distance via the body's fluid media. Biogenic amines and protein-nature substances (hormones, oligopeptides) act as transmitters.
Three modes of function regulation
When it comes to the targeted subordination of structures, three main control modes operate in the body:
- Nervous regulation. Implemented exclusively by the nervous system. Its main distinguishing feature is immense speed. Neural influences are carried out very rapidly.
- Humoral regulation. Occurs through chemical substances circulating in the 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 neural signals, humoral influences are relatively slow.
- Neurohumoral regulation. This is a combination of the two previous pathways. It is the primary form of regulation in the intact organism.
Mechanisms of neurohumoral interaction
Neurohumoral regulation demonstrates how neural and humoral mechanisms complement each other. The interaction between them is built on two main scenarios.
The first mechanism is the 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.
The second mechanism is the simultaneous effect on an organ. In such a situation, the target organ receives commands simultaneously through both channels. Neural influences are implemented quickly but act briefly, ensuring an immediate reaction. Humoral influences arrive later, yet act more persistently, maintaining the function at the required level.
Briefly: answers to topical questions
Which biogenic amines are involved in the distant pathway of chemical correlation?
In the distant pathway of chemical correlation, which is mediated through the body's fluid media, biogenic amines act as agents.
In the cited sources, biogenic amines include:
- histamine;
- serotonin;
- catecholamines: epinephrine and norepinephrine;
- melatonin.
Sources also indicate that the pineal gland synthesizes biogenic amines: melatonin, serotonin, norepinephrine, histamine, etc.
What is the structure of gap junctions between the membranes of neighboring cells?
Gap junctions are zones where the plasmalemmas of neighboring cells approach each other to a distance of 2–4 nm, penetrated by specialized channels. The structure of these units includes:
- Connexins — transmembrane integral proteins spanning the cell membrane.
- Connexons — protein complexes formed by six connexin globules.
Transmembrane proteins of one cell are located strictly opposite the proteins of another cell. Connexins surround a central hydrophilic pore with a diameter of 1.5 nm, forming a channel that ensures bidirectional exchange between cells.
The nervous system is like a telegram (fast, but short-lived). The humoral system is like a regular letter (takes a long time to arrive, but contains a long text for the future). The neurohumoral system is the ideal tandem of both types of communication.
Class and exam questions
What are gap junctions?
These are fusion zones of adjacent membrane regions of neighboring cells. They provide the contact type of chemical correlation, allowing cells to directly exchange protoplasm and biologically active substances.
Which fluids are involved in humoral regulation?
Humoral regulation factors circulate in all major fluid media of the body: blood, lymph, tissue fluid, and cerebrospinal fluid.
How do neural and humoral signals jointly affect a single organ?
They work as a mutually complementary tandem. Neural signals are implemented first, providing a fast but short response. Humoral factors act later, but their effect lasts significantly longer.
What else to study on this topic
- The role of chemical correlation in the directed growth of nerve fibers in embryogenesis
- Types and functions of messenger substances in distant chemical correlation (biogenic amines, oligopeptides)
- Physiological examples of mechanical correlation of internal organs
- Mechanisms of primary exposure of humoral agents to CNS neural centers
- Differences between humoral regulation and contact chemical correlation
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